TECHNICAL FIELD

[0001] The application relates to using a pulsed laser to modify the refractive index of an optical medium, and particularly to writing refractive index changes into ocular tissues or replacement or augmentative structures to modify or enhance the visual performance of patients.

BACKGROUND OF THE INVENTION

[0002] Pulsed lasers operating within specified regimes specially adapted to target optical materials have been demonstrated to produce localized refractive index changes in the optical materials without otherwise damaging the materials in ways that would impair vision. The energy regimes, while above the nonlinear absorption threshold, are typically just below the breakdown thresholds of the optical materials at which significant light scattering or absorption degrades their intended performance. The considerations of these adapted energy regimes include pulse wavelength, pulse energy, pulse duration, the size and shape into which the pulses are focused into the optical material, and the temporal and physical spacing of the pulses.

[0003] Examples include US Patent Application Publication No. 2013/0226162 entitled Method for Modifying the Refractive Index of Ocular Tissues, which discloses a laser system for changing the index of refraction of cornea tissue in a living eye for forming of modifying optical elements including Bragg gratings, microlens arrays, zone plates, Fresnel lenses, and combinations thereof. Here wavelengths are preferably between 400 nm and 900 nm, pulse energies are preferably between 0.01 nJ and 10 nJ, pulse duration is preferably between 10 fs and 100 fs, the repetition rate is preferably between 10 MHz and 500 MHz, the numerical aperture is preferably about 0.70 producing about a line width between approximately 0.6 pm to 1 .5 pm and a line depth between 0.4 pm to 8 pm, and the scan rate is between approximately 0.1 pm/s to 10 mm/s. US Patent Application Publication No.

2013/0268072 entitled Optical Hydrogel Material with Photosensitizer and Method for Modifying the Refractive Index discloses a method for modifying the refractive index of an optical, hydrogel polymeric material prepared with a photosensitizer particularly for the purposes of enhancing the efficiency of nonlinear absorption and increasing the scan rate at which refractive structure can be formed. Wavelengths are preferably between 650 nm to 950 nm, pulse energies are preferably between 0.05 nJ to 10 nJ, pulse duration is preferably between 4 fs and 100 fs, the repetition rate includes by way of example both 80 MHz and 93 MHz, the numerical aperture is preferably about 0.70 producing about a line width between approximately 0.6 pm to 10.5 pm and a line depth between 1 pm to 4 pm, and the scan rate is between approximately 0.1 pm/s to 4 mm/s. US Patent Application Publication No. 2015/0126979 entitled Method for Modifying the Refractive Index of an Optical Material discloses the writing of selected regions of optical hydrogel materials prepared with a hydrophilic monomer following implantation of the prepared material into the eye of the patient. Wavelengths are preferably between 600 nm to 900 nm, pulse energies are preferably between 0.01 nJ to 50 nJ, pulse duration is preferably between 4 fs and 100 fs, the repetition rate includes by way of example 93 MHz, the numerical aperture is preferably about 0.70 producing about a line width between approximately 0.2 pm to 3 pm and a line depth between 0.4 pm to 8 pm, and a demonstrated scan rate is approximately 0.4 pm/s. US Patent Application Publication No. 2015/0378065 entitled Method for Modifying the Refractive Index of an Optical Material and resulting Optical Vision Component, which discloses the writing of GRIN layers in optical polymeric materials. Wavelengths are preferably between 750 nm to 1100 nm, pulse energies are preferably between 0.01 nJ to 20 nJ, pulse duration is preferably between 10 fs and 500 fs, the repetition rate is preferably between 10 MHz and 300 MHz, the numerical aperture is preferably about 0.70 producing about a line width between approximately 0.6 pm to 3 pm and a line depth between 0.4 pm to 8 pm, and the scan rate is between approximately 0.1 mm/s to 10 mm/s. These referenced patent applications are hereby incorporated by reference, particularly as examples for writing refractive structures in optical materials, and as representative background technologies subject to the improvements set forth herein.

[0004] While more opportunities exist for synergies between the adapted energy regimes and man-made optical materials, the speed and efficiency with which refractive index changes can be written into the optical materials remains of importance whether the optical materials are of living origin or man-made, and whether the optical materials are positioned in vivo or in vitro. Constraints relating to the need to deliver concentrated pulse energies of a laser beam in a form that achieves the desired refractive index changes in the optical materials without exceeding the damage threshold at which the desired optical performance is degraded have limited the speed and efficiency with which refractive index structures can be written into the optical materials. WO2018/182946 discloses refractive writing systems including various beam multiplexer arrangements introducing additional diverse beam paths to generate multiple focused scanned spots while essentially maintaining effective numerical apertures for each focused scanned beam through an objective lens relative to the source laser beam which is multiplexed, where control of the multiple distinct focused beams is useful for more effective writing of refractive index changes in optical materials without exceeding the damage threshold at which the desired optical performance is degraded. It would be further useful to develop additional multiplexing systems for generating multiple scanned focus spots from a source laser beam which would reduce or eliminate the need for introducing, or the number of, diverse beam paths introduced relative to the number of focused scanned spots obtained in refractive writing systems.

SUMMARY

[0005] An embodiment as envisioned by the inventor incorporates a spatio-temporal- angular beam multiplexer for cross-sectionally dividing a first laser beam cross- sectional area into sub-sections forming at least two working beams from the first laser beam that are angularly and temporally differentiated from each other to expand opportunities for improving the speed and efficiency with which refractive index structures can be written into a variety of optical materials. The opportunities include increasing the speed at which regions are scanned in the optical materials, achieving greater refractive index changes along the scanned regions, improving continuity or control over the refractive index changes along or between regions, expanding the width or thickness over which the refractive index changes are made along the scanned regions, and scanning over multiple regions within or between designated layers of the optical materials. The pulses of the multiplexed working beams can be spatially offset to spread the pulses throughout a greater volume for increasing the size of a common volume subject to refractive index change along the same scanned region or subjecting different volumes to the same or different refractive index changes along multiple scanned regions, and temporally offset to increase the effective repetition rate at which pulses are delivered to the optical materials. The temporal and spatial relationships among the different separated working beam pulses delivered to the optical material can also be adapted to affect the sizes and shapes of temperature profiles generated along the same or adjacent scan regions to achieve desired refractive index changes over larger volumes while avoiding the damage thresholds at which the materials undergo undesired changes that would degrade their optical performance. The refractive index changes written into the optical material include relatively increasing or decreasing the refractive index of the scanned regions of the optical material according to the local reaction of the optical material to the pulses delivered.

[0006] In addition to controlling the temporal and spatial relationships between the pulses of the different working beams delivered to the optical materials, the characteristics of the pulses within different sets of working beams or the different working beams themselves within which the pulses are delivered can be altered or otherwise controlled. For example, the pulse energy or the pulse width of the pulses in different sets of working beams can be relatively altered as well as the volumes through which the different working beams are focused. In fact, the pulse characteristics can be further relatively altered to accommodate the different size and shape volumes that can be associated with writing at extended depths in the optical material. For example, the pulses can be elongated in the direction of propagation, which allows more power to be delivered for effecting refractive index changes over an extended depth while remaining below the threshold of optical damage.

[0007] The change in refractive index that can be effected by any one dose of actinic radiation in optical materials, such as corneal tissue or hydrogels, is limited by the damage thresholds of the materials. As such, the change in refractive index is generally too small to support 2TT phase changes, which are often needed to minimize phase discontinuities in Fresnel or other types of segmented optical structures written into the optical materials. However, by writing over extended depths, only one or at least fewer layers may be required to be written to effect 2TT phase changes. Writing the refractive index changes over extended depths makes possible faster and more accurate writing of such optical structures, as well as higher and more efficient optical performance. BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0008] FIG. 1 is a simplified schematic illustration of a refractive index writing system in accordance with an embodiment of the present disclosure for writing traces along a scan region in an optical material.

[0009] FIG. 2 is a simplified schematic illustration of an embodiment of the scanning/interface assembly of the embodiment of Fig. 1 .

[0010] Figs. 3A-3B are plane and side views of an optical plate beam multiplexer comprising a plurality of wedge sections in accordance with an embodiment of the present disclosure.

[0011 ] Fig. 3C, is a schematic illustrating angular deviation <T» for a divided working beam from a first laser beam propagation axis determined by the wedge section angle Q forming the divided working beam.

[0012] Fig. 3D is a schematic illustrating temporal separation (AT) of the pulses of divided working beams as a function of the divided working beams passing through wedge sections having different average thickness.

[0013] Fig. 3E is a schematic illustrating a multiplexer plate with four wedge sections having different wedge angles and average wedge thicknesses employed with a common objective lens to generate four focused pulses arriving at four different spots at different times from a single first generated laser beam which is divided by the multiplexer plate.

[0014] FIG. 4A is a diagram of a two-beam multiplexer that initially splits the output beam of a pulsed laser into two orthogonally polarized working beams and then recombines the two working beams for writing refractive index changes into an optical material.

[0015] FIG. 4B is a diagram of the recombined orthogonally polarized working beams of FIG. 4A showing a temporal offset between the two beams.

[0016] FIG. 5 is a diagram of a focusing system including an objective lens for converting two angularly offset working beams into two spatially offset working beams that are focused to different locations within the same transverse plane in an optical material.

[0017] FIG. 6 is a diagram of a set of parallel traces written into the optical material by scanning the focused working beams along a Y coordinate axis perpendicular to the spacing between the focal spots of the working beams in a raster pattern that indexes subsequent scans along an X coordinate axis for changing the refractive index of the optical material over the scanned region.

[0018] FIG. 7 is a similar diagram of a set of parallel traces written into the optical material by scanning the focused working beams along an X coordinate axis parallel to the spacing between the focal spots of the working beams in a raster pattern that indexes subsequent scans along a Y coordinate axis for changing the refractive index of the optical material over the scanned region.

[0019] FIG. 8 is a similar diagram of a set of parallel traces written into the optical material by scanning temporally offset working beams focused to coincident focal spots along a Y coordinate axis a raster pattern that indexes subsequent scans along an X coordinate axis for changing the refractive index of the optical material over the scanned region.

[0020] FIG. 9 is a graph showing temperature gradients in the optical material associated with the scanning of a focal spot along one of the coordinate axes.

[0021] FIG. 10 is a diagram of an alternative two-beam multiplexer with a beam shaper along the region of one of two orthogonally polarized working beams combined with an objective lens for focusing the two working beams at different depths within an optical material.

[0022] FIG. 11 is a greatly enlarged depiction of the focal spots of FIG. 7 scanning two linear traces at different depths in the optical material.

[0023] FIGS. 12A and 12B present graphs plotting phase change in an optical material as a function of applied optical power, demonstrating the additional optical power that can be applied to extended depth focal spots while remaining below a damage threshold of the optical material. [0024] FIG. 13 is a diagram of a two-beam multiplexer similar to the multiplexer of FIG. 10 with the addition of two spherical aberration correction plates for elongating the focal spots produced by the two working beams.

[0025] FIG. 14 is a greatly enlarged depiction of two extended depth focal spots produced by the working beams of FIG. 13.

[0026] FIG. 15 is a graph plotting the intensities of focal spots in an axial plane for focal spots produced with zero spherical aberration, a first amount of positive spherical aberration, and a second higher amount of positive spherical aberration.

[0027] FIG. 16 is a diagram of an optomechanical scanner for translating the focal spots of any of the beam multiplexers referenced herein along three orthogonal axes for writing refractive index structures in an optical material.

DETAILED DESCRIPTION OF THE INVENTION

[0028] FIG. 1 is a simplified schematic illustration of a refractive index writing system 1030 for writing traces along a scan region in an optical material such as an ophthalmic lens 1010, where the traces are defined by a controlled change in refractive index in accordance with embodiments of the present disclosure. The system 1030 may include, e.g., a laser beam source 1032, a laser beam intensity control assembly 1034, a laser beam pulse control assembly 1036, a scanning/interface assembly 1038, and a control unit 1040.

[0029] The laser beam source 1032 generates and emits a laser beam 1046 having a suitable wavelength for inducing refractive index changes in target sub-volumes of the ophthalmic lens 1010. In examples described herein, the laser beam 1046 has a 1035 nm central wavelength. The laser beam 1046, however, can have any suitable wavelength (e.g., in a range from 400 to 1100 nm) effective in inducing refractive index changes in the ophthalmic lens 1010.

[0030] The laser beam intensity control assembly 1034 is controllable to selectively vary intensity of the laser beam 1046 to produce a selected intensity laser beam 1048 output to the laser beam pulse control assembly 1036. The laser beam intensity control assembly 1034 can have any suitable configuration, including any suitable existing configuration, to control the intensity of the resulting laser beam 1048, such as an electro-optic modulator or an acousto-optic modulator, for variably attenuating the beam 1048. The laser beam pulse control assembly 1036 can have any suitable configuration, including any suitable existing configuration, to control the duration of pulses in a resulting pulsed laser beam 1050. The laser beam source 1032, laser beam intensity control assembly 1034, and laser beam pulse control assembly 1036 are together controllable to generate a substantially collimated pulsed laser beam output 1050 having suitable duration, intensity, size, and spatial profile, and having a first laser beam propagation axis and a first laser beam cross sectional area.

[0031] A spatio-temporal-angular beam multiplexer 1051 is configured for cross- sectionally dividing the first laser beam cross sectional area of laser beam output 1050 into sub-sections forming at least two working beams 1050A, 1050B ...1050N from the pulsed laser beam output, which working beams are generally adjacent to each other and delivered to scanning/interface assembly 1038, which includes an objective lens configured for receiving and simultaneously focusing the at least two working beams to spatially and temporally separated focal spots in the optical material; and a scanner configured for moving the separated focal spots with respect to the optical material at a relative speed and direction for writing one or more traces along a scan region in the optical material defined by a controlled change in refractive index. More particularly, the scanning/interface assembly 1038 is controllable to selectively scan the at least two working beams 1050A, 1050B, ...1050N to produce corresponding XYZ scanned laser focal points 1074A, 1074B, ...1074N. The scanning/interface assembly 1038 can have any suitable configuration, including any suitable existing configuration (for example, the configuration illustrated in FIG. 2) to produce the XYZ scanned laser focal points 1074A, 1074B, ...1074N. The scanning/interface assembly 38 receives the at least two working beams 1050A, 1050B, ...1050N and outputs the XYZ scanned laser focal points 1074A, 1074B, ...1074N in a manner that preferably minimizes vignetting. The scanning/interface assembly 1038 is controlled to scan each of the at least two working laser beams 1050A, 1050B, ... 1050N to generate XYZ scanned laser focal points 1074A, 1074B, ...1074N in the ophthalmic lens 1010 to induce refractive index changes in targeted sub- volumes so as to form one or more subsurface optical structures within an ophthalmic lens 1010. [0032] In such regard, the laser beam source 1032, laser beam intensity control assembly 1034, and laser beam pulse control assembly 1036 are together selected and are controllable to generate a substantially collimated pulsed laser beam output 1050 having suitable duration, intensity, size, and spatial profile so as to enable such separation in to a plurality of working beams and generation of a corresponding plurality of separated focal spots of sufficient intensity for inducing refractive index changes in the target sub-volumes of the ophthalmic lens 1010.

[0033] In many embodiments, the scanning/interface assembly 1038 may be further configured to restrain the position of the ophthalmic lens 1010 to a suitable degree to suitably control the location of the targeted sub-volumes of the ophthalmic lens 1010 relative to the scanning/interface assembly 1038. In many embodiments, such as the embodiment illustrated in FIG. 2, the scanning/interface assembly 1038 may include a motorized Z-stage that is controlled to selectively control the depth within the ophthalmic lens 1010 of each of the XYZ scanned laser focal points 1074A, 1074B, ...1074N.

[0034] Control unit 1040 is operatively coupled with each of the laser beam source 1032, the laser beam intensity control assembly 1034, the laser beam pulse control assembly 1036, and the scanning/interface assembly 1038. The control unit 1040 provides coordinated control of each of the laser beam source 1032, the laser beam intensity control assembly 1034, the laser beam pulse control assembly 1036, and the scanning/interface assembly 1038 so that each of the XYZ scanned focal points 1074A, 1074B, ...1074N have a selected intensity and duration, and are focused onto a respective selected subvolume of the ophthalmic lens 1010 to form one or more subsurface optical structures within an ophthalmic lens 1010. In particular, the scanner is adjustable for setting the relative speed and direction of the simultaneously scanned separated focal spots for maintaining an energy profile within the optical material along the scan region above a nonlinear absorption threshold of the optical material and below a breakdown threshold of the optical material at which significant light scattering or absorption degrades the intended performance of the optical material.

[0035] The control unit 1040 can have any suitable configuration. For example, in some embodiments, the control unit 1040 comprises one or more processors and a tangible memory device storing instructions executable by the one or more processors to cause the control unit 1040 to control and coordinate operation of the laser beam source 1032, the laser beam intensity control assembly 1034, the laser beam pulse control assembly 1036, and the scanning/interface assembly 1038 to produce the XYZ scanned focal points 1074A, 1074B, ...1074N.

[0036] FIG. 2 is a simplified schematic illustration of an embodiment of the scanning/interface assembly 1038. In the illustrated embodiment, the scanning/interface assembly 1038 includes an XY galvo scanning unit 1042, a relay optical assembly 1044, a Z stage 1066, an XY stage 1068, a focusing objective lens 1070, and a patient interface/ophthalmic lens holder 1072. The XY galvo scanning unit 1042 includes XY galvo scan mirrors 1054, 1056. The relay optical assembly 1044 includes concave mirrors 1060, 1061 and plane mirrors 1062, 1064.

[0037] The XY galvo scanning unit 1042 receives the at least two working laser beams 1050A, 1050B, ...1050N (e.g., 1035 nm central wavelength collimated laser pulses) from the spatio-temporal-angular beam multiplexer 1051 . While the working beams are angularly offset, this is not illustrated in Fig. 2 for clarity. In the illustrated embodiment, the XY galvo scanning unit 1042 includes a motorized X-direction scan mirror 1054 and a motorized Y-direction scan mirror 1056. The X-direction scan mirror 1054 is controlled to selectively vary orientation of the X-direction scan mirror 1054 to vary direction/position of XY scanned working laser beams 1058A, 1058B, ...1058N in an X-direction transverse to direction of propagation of the XY scanned working laser beams 1058A, 1058B, ...1058N. The Y-direction scan mirror 1056 is controlled to selectively vary orientation of the Y-direction scan mirror 1056 to vary direction/position of the XY scanned working laser beams 1058A, 1058B, ...1058N in a Y-direction transverse to direction of propagation of the XY scanned working laser beams 1058A, 1058B, ...1058N. In many embodiments, the Y-direction is substantially perpendicular to the X-direction.

[0038] The relay optical assembly 1044 receives the XY scanned working laser beams 1058A, 1058B, ...1058N from the XY galvo scanning unit 1042 and transfers the XY scanned working laser beams 1058A, 1058B, ... 1058N to the Z stage 1066 in a manner that minimizes vignetting. Concave mirror 1060 reflects each of the XY scanned working laser beams 1058A, 1058B, ...1058N to produce converging laser pulses incident on plane mirror 1062. Plane mirror 1062 reflects the converging XY scanned working laser beams 1058A, 1058B, ...1058N towards plane mirror 1064. Between the plane mirror 1062 and the plane mirror 1064, the XY scanned working laser beams 1058A, 1058B, ...1058N transition from being convergent to being divergent. The divergent working laser beams 1058A, 1058B, ...1058N are reflected by plane mirror 1064 onto concave mirror 1061. Concave mirror 1061 reflects the working laser beams 1058A, 1058B, ...1058N to produce collimated working laser beams that are directed to the Z stage 1066.

[0039] The Z stage 1066 receives the XY scanned working laser beams 1058A, 1058B, ...1058N from the relay optical assembly 1044. In the illustrated embodiment, the Z stage 1066 and the XY stage 1068 are coupled to the focusing objective lens 1070 and controlled to selectively position the focusing objective lens 1070 relative to the ophthalmic lens 1010 so as to focus the XYZ scanned laser focal points 1074A, 1074B, ...1074N in the ophthalmic lens 1010. The Z stage 1066 is controlled to selectively control the depth within the ophthalmic lens 1010 at which the scanned working laser beams are focused. The XY stage 1068 is controlled in conjunction with control of the XY galvo scanning unit 1042 so that the focusing objective lens 1070 is suitably positioned for the respective transverse position of each of the XY scanned working laser beams. The focusing objective lens 1070 simultaneously converges each of the scanned working laser beams 1058A, 1058B, ...1058N in the lens 1010. The patient interface/ophthalmic lens holder 1072 restrains the ophthalmic lens 1010 in a fixed position to support scanning of the laser pulses 1074 by the scanning/interface assembly 1038 to form the subsurface optical structures.

[0040] After being formed by the spatio-temporal-angular beam multiplexer 1051 cross-sectionally dividing the source laser beam, the at least two working beams 1050A, 1050B ...1050N are angularly and temporally differentiated from each other, but are still generally adjacent to each other and subsequently can advantageously take a generally common path from the spatio-temporal-angular beam multiplexer 1051 through the scanning/interface assembly 1038 to a common objective lens 1070 for focusing the working beams to focal spots in an optical material.

[0041] In many embodiments, spatio-temporal-angular beam multiplexer 1051 is configured for cross-sectionally dividing the first laser beam cross sectional area into three or more sub-sections, and the at least two working beams 1050A, 1050B, ...1050N comprise three or more working beams that are angularly and temporally differentiated from each other formed from the three or more sub-sections. In a particular embodiment as shown in Figs. 3A-3B, the spatio-temporal-angular beam multiplexer 1051 is configured for cross-sectionally dividing the first laser beam cross sectional area into four quadrants Q1 , Q2, Q3, Q4, and the at least two working beams 1050A, 1050B, ...1050N will comprise four working beams that are angularly and temporally differentiated from each other formed from the divided four quadrants. While the divided subsections of the first laser beam cross sectional area in various embodiment may be equally or non-equally divided subsections, in a particular embodiment employing the spatio-temporal-angular beam multiplexer of Figs. 3A-3B the divided four quadrants are of equal areas.

[0042] As further shown in Figs. 3A-3B, the beam multiplexer 1051 may comprise an optical plate comprising a plurality of wedge sections each having different wedge angles and configured for directing each of the two or more working beams to different angles from each other relative to the first laser beam propagation axis of the pulsed laser beam output. As shown in Fig. 3C, e.g., an angular deviation 0 for a divided working beam from the first laser beam propagation axis will be determined by the individual wedge section angle 0 forming the divided working beam in accordance with the formula: 0= (n-1) * 0. To maintain all of the separated divided working beams within the common objective lens 1070 for focusing in the optical material, the wedge section angles may be maintained small, although this will limit separation of the focal spots from the first laser beam propagation axis. Significantly, however, by providing multiple wedge angles, each providing an angular deviation for a divided working laser beam from the first laser beam propagation axis, and positioning the multiple wedges of the beam multiplexer around the first laser beam propagation axis, the relative angular deviation between two divided working beams may be increased beyond that of each working beam relative to the first laser beam propagation axis, thus increasing the obtainable separation distance between the resulting corresponding focal spots for the divided working beams focused with a common objective lens.

[0043] In accordance with many embodiments, at least two wedge sections of the plurality of wedge sections may have different average wedge thicknesses configured for temporally differentiating at least two of the two or more working beams from each other. As illustrated in Fig. 3D, e.g. , where the wedge sections have different average thickness, the divided working beams will also result in temporal separation (AT) of the pulses of the working beams in accordance with the formula AT= (n-1 ) Ax/c where Ax is the difference in average thickness between two wedge sections. Although the temporal separation may be relative short, such temporal separation of pulses in adjacent scanned spots can still help control or minimize thermal interaction between the scanned focal spots to help achieve refractive index change while avoiding material damage. Thus, as shown in Fig. 3E, a multiplexer plate with four wedge sections having different wedge angles and average wedge thicknesses may be employed with a common objective lens to generate four focused pulses arriving at four different spots 1074A, 1074B, ...1074N at different times from a single first generated laser beam which is divided by the multiplexer plate. Note that while Fig. 3E depicts the microscope objective 1070 adjacent to the multiplexer plate 1051 for focusing each of the divided quadrants of the source laser beam to form the four separated focal spots, a scanning unit and optical relay will typically be positioned between the multiplexer plate 1051 and objective lens as illustrated in Fig. 2. The objective lens magnification, wedge angles for each wedge section of the multiplexer plate 1051 , and effective numerical aperture for each of the divided working beams may be selected in combination with the controlled source laser beam 1050 properties and scan rates to obtain desired individual focal spot energies and relative focal spot X, Y, Z spacings to achieve desired effective refractive index change structures written in a given optical material upon scanning of the focal spots. In various embodiments, depending upon desired results, the spaced focal spots may be simultaneously scanned in desired X, Y, and or Z directions to write multiple spaced parallel lines, and or to scan in a direction linearly connecting at least 2 spaced focal spots to increase the exposure energy along the scan direction.

[0044] The beam multiplexer 1051 comprising an optical plate with a plurality of wedge sections may be formed from optical glass employing known fabrication techniques. For example, N-BK7 glass wedges may be manufactured by precision grinding. Such glass wedge devices are inherently achromatic, and can be used at any wavelength laser. They may be AR coated (nearly lossless), and may be used in combination with other multiplexing schemes to provide even greater number of working laser beams. In alternative embodiments, the beam multiplexer 1051 may comprise a phase modulator, such as a liquid crystal on silicon (LCOS) phase modulator, configured with sectional phase ramps for cross-sectionally dividing and selectively phase-shaping the first laser beam cross sectional area of laser beam output 1050 into sub-sections forming the at least two working beams 1050A, 1050B ...1050N from the pulsed laser beam output.

[0045] In a further embodiment, a beam multiplexer 1051 may be used in combination with a polarization splitting multiplexer to effectively further double the number of separated focal spots that may be generated from a single first laser beam. The optical plate beam multiplexer 1051 , e.g., is itself polarization-insensitive, and thus may be used in combination with a polarization beam splitting system such as described in WO2018/182946, the disclosure of which is incorporated by reference herein in its entirety.

[0046] In a polarization splitting multiplexer such as described in WO2018/182946, and as shown in FIGS. 4A and 4B, a laser source 12 outputs a collimated substantially linearly polarized beam 14, whose polarization axis is rotated by a halfwave plate 16 to an orientation substantially at 45 degrees to the orthogonal polarization axes of a first polarization beamsplitter 18.

[0047] The first polarization beamsplitter 18 divides the collimated output beam 14 into two orthogonally polarized working beams 20 and 22. For example, the working beam 20, which transmits through the first polarization beamsplitter, has a polarization axis oriented in a horizontal plane extending out of the drawing sheet, and the working beam 22, which is reflected by the first polarization beamsplitter, has a polarization axis oriented in a vertical plane within the drawing sheet. The horizontally polarized working beam 20 propagates directly to a second beamsplitter 28. Reflectors 24 and 26 direct the vertically polarized working beam 22 to the second beamsplitter 28 in a physical orientation that remains orthogonal to the physical orientation of the working beam 20. The second polarization beam splitter 28 transmits the horizontally polarized working beam 20 and reflects the vertically polarized working beam 22 into realignment with the working beam 20. [0048] While physically aligned as output from the second polarization beamsplitter 28, the working beams 20 and 22 remain distinguished by their relative orthogonally related polarizations as shown in FIG. 4B. Arrows depict the equally spaced timing of the femtosecond pulses 30 of the working beam 20 at a given repetition rate preferably in the MHz range, which are shown in a horizontal orientation as a further indication of the horizontal polarization orientation of the working beam 20. In a complementary fashion, arrows depict the equally spaced timing of the femtosecond pulses 32 of the working beam 22 at the given repetition rate, which are shown in a vertical orientation as a further indication of the vertical polarization orientation of the working beam 22.

[0049] Although the two working beams 20 and 22 are realigned at the output of the second polarization beamsplitter 28, the pulses 30 and 32 of the respective working beams 20 and 22 are temporally offset by At as a result of an optical path length difference, which can include a delay element 34 along one of the separate paths taken by the working beams 20 and 22 between the first and second polarization beamsplitters 18 and 28. Alternatively, the reflectors 24 and 26 could be collectively displaced toward or away from the first and second beamsplitters 18 and 28 with which they are aligned to change the optical path length of the working beam 22 with respect to the optical path length of the working beam 20. The temporal offset At can be set to vary by any amount less than the temporal spacing between the pulses as the inverse of the repetition rate. For example, at a repetition rate of 100 MHz, the pulses are temporally spaced by about 10 ns and physically spaced by 3 m. In the combined beams 20 and 22, temporal offset At by one half of the spacing between pulses (e.g., 5 ns at 100 MHz), the repetition rate in the combined beam is effectively doubled (e.g., 200 MHz). Other temporal offsets At can be used for other purposes including regulating temperature profiles in the irradiated optical materials associated with the delivery of closely adjacent pulses.

[0050] The arrows of FIG. 4B representing the pulses 30 and 32 of the respective working beams 20 and 22, while in different planes, are drawn at approximately equal lengths representative of equal pulse energies between the pulses 30 and 32. However, the pulse energies can also be unequally distributed between the pulses 30 and 32 of the respective working beams 20 and 22, such as by rotating the halfwave plate 16 to a different angular position and thereby orienting the polarization axis of the output beam 14 closer to one or the other of the orthogonal polarization axes of the first polarization beamsplitter 18 (i.e. 45°).

[0051 ] Thus, in addition to controlling the temporal offset At of the pulses 30 and 32 in the respective orthogonally polarized working beams 20 and 22, the relative pulse energies of the pulses 30 and 32 can also be controlled to regulate the delivery of energy to the optical materials intended for irradiation. Moreover, the overall pulse energies of the two beams can be controlled by a modulator 33, such as an electrooptic modulator or an acousto-optic modulator, for variably attenuating the output beam 14. The overall pulse energies and the relative pulse energies of the two working beams 20 and 22, as well as the temporal offset At between the pulses of the two working beams 20 and 22 can be manually controlled by settings or can be automatically controlled through a controller 35 that takes input from an operator.

[0052] The different polarization orientations of the two aligned working beams 20 and 22 also allow for subsequent angular or spatial separation of the two beams. In addition, small angular separations can be made in advance of the second polarization beamsplitter 28. For example, the reflector 26 can be tipped slightly out of a 45 degree orientation to its incident beam to relatively incline the working beam 22 with respect to the working beam 20 as output from the second beamsplitter 28.

[0053] FIG. 5 shows a focusing system the two orthogonally polarized and relatively inclined working beams 20 and 22 reflected by a reflector 36 into desired alignment with an objective lens 38, which focuses the two working beams 20 and 22 to spatially offset focal spots 40 and 42 in an optical material 44. The objective lens 38, which is considered as a part of the beam multiplexer system 10, converts an angular difference Aa between the working beams 20 and 22 into a spatial offset As, which is measured on center between the focal spots 40 and 42. As shown, the two focal spots 40 and 42 are offset through the measure As in a common plane 46 oriented transverse to the optical axis 39 of the objective lens 38. In advance of the objective lens 38, the working beam 20 is aligned with the optical axis 39 and the working beam 22 is inclined to the optical axis 39 through angle Aa. However, either or both of the working beams 20 and 22 can be inclined to the optical axis 39 to produce the desired angular difference Aa. As shown, the two working beams 20 and 22 diverge in advance of the objective lens 38. However, the two working beams could also be arranged to converge at the objective lens 38 to minimize the required size of the objective lens 38 to receive both beams. Both working beams 20 and 22 may have a transverse dimension (e.g., width) sufficient to substantially fill the aperture of the objective lens 38 to form highly resolved focal spots 40 and 42.

[0054] In a further embodiment of the present disclosure, a polarization multiplexing beam splitter system such as described above and in WO2018/182946 generating two differentially polarized relatively inclined working beams 20 and 22 may be employed in combination with an optical plate beam multiplexer 1051 placed in the laser beam path after the two working beams 20 and 22 are aligned, such that the aligned working beams 20 and 22 are both divided by the wedge sections of the optical plate beam multiplexer 1051 , thereby forming two differentially polarized and relatively differentially angularly offset working laser beams at each wedge section, resulting in two sets of working beams 1050A’, 1050B’, ...1050N’ (e.g., from working beam 20 divided by beam multiplexer 1051) and 1050A”, 1050B”, ...1050N” (from working beam 22 divided by beam multiplexer 1051) to effectively double the number of separated scanned focal spots obtainable with the optical plate beam multiplexer 1051 alone.

[0055] As respective treatment zones, the focal spots 1074A, 1074B, ...1074N occupy respective volumes of space within which the power densities of the respective working beams 1050A, 1050B, ...1050N are sufficient to change the refractive index of the optical material without inducing damage. Positive or negative changes in refractive index can be imparted by the respective working beams depending upon the reaction of the optical material to the pulses delivered by the beams.

[0056] The objective lens 1070 can take the form of a microscope objective having a nominal numerical aperture of preferably at least 0.28 but higher numerical apertures of 0.7 through 1 .0 are often preferred if sufficient working distance is present. The effective numerical aperture for each divided working beam focused by the objective lens, however, is preferably less than 0.50. Generally, for the purpose of writing refractive index structures in optical materials, with pulsed laser sources, the succession of pulses preferably have a pulse width between 8 fs and 500 fs, a pulse energy between 0.1 nJ and 150 nJ, a repetition rate between 5 MHz and 500 MHz, and a nominal wavelength in the visible or near infrared range, typically between 400 nm and 1100 nm. Useful representative wavelength ranges include 500 to 550 nm, 1000 to 1100 nm, 400 to 420 nm, and 700 to 850 nm. These parameters are also tied to the focal spot size and the scanning rate at which the focal spot is moved relative to the optical material. For writing refractive index changes over larger volumes, both the focal spot size and the scanning rate are increased as much as practically possible in coordination with the other parameters that are set to operate in an energy regime just below the damage threshold of the material. Scanning speeds up to 10 m/s and higher are contemplated.

[0057] In some embodiments, a laser pulse width and a laser effective NA may be selected for a given focused laser average power range to increase the laser damage threshold relative to use of laser pulse widths shorter than the selected laser pulse width and/or use of laser effective NAs greater than the selected laser effective NA, as disclosed in WO2021/108585, the disclosure of which is incorporated herein in its entirety. In specific embodiments, the pulsed laser source, beam multiplexer, and objective lens are configured to form the at least two working beams each having a laser pulse width of greater than about 165 fs, a working beam effective Numerical Aperture of less than 0.50, and a focused laser average power of from 1 to 5000 mW. In such embodiments, the at least two working beams more specifically may each have a laser pulse width of greater than or equal to about 180 fs, at least about 200 fs, at least about 210 fs, at least about 250 fs, at least about 300 fs, or at least about 350 fs. Further in such embodiments, the at least two working beams may each have a laser pulse width of less than or equal to about 500 fs, or of less than or equal to about 400 fs. Further in such embodiments, the at least two working beams each have effective Numerical Aperture of less than or equal to about 0.49, or of less than or equal to about 0.4, or of less than or equal to about 0.3, or of less than or equal to about 0.26, or of less than or equal to about 0.25, or of less than or equal to about 0.20, or of less than or equal to about 0.19. Further in such embodiments, the at least two working beams may each have an effective Numerical Aperture of greater than or equal to about 0.05, or of greater than or equal to about 0.1.

[0058] While pairs of the focal spots 1074A, 1074B, ... 1074N remain separated through a spatial offset As, the objective lens 1070 can be moved relative to the optical material 1010 in different directions to write pairs of linear traces having a line spacing ranging from zero to the spatial offset As. FIG. 6, for example, depicts the simultaneous writing of parallel traces 50 and 52 at a line spacing equal to the spatial offset As for doubling the line density that can be produced by each scan in the direction of the Y coordinate axis. The working beam 40 writes the traces 50, and the working beam 42 writes the traces 52. Each scan is indexed by an amount Ax along the X coordinate axis that is equal to twice the spatial offset As between the focal spots 40 and 42. The scans of the two focal spots 40 and 42 along the Y coordinate axis are repeated at different starting locations by successively shifting or otherwise indexing the focal spots 40 and 42 along the X coordinate axis by increments Ax to write the overall raster pattern shown. Of course, the dimensions depicted on the drawing figures are not to scale. For example, a typical line spacing is approximately 0.5 pm, and the angular difference Aa between the working beams 20 and 22 for such a line spacing can be in the range of 0.01 degrees. Any lesser line spacing, i.e. , a line spacing less than the spatial offset As between the focal spots 40 and 42, can be achieved by changing the direction of the scan from a direction perpendicular to a line connecting focal spots 40 and 42 to a direction closer to parallel to the connecting line. Doubling the line density by writing two linear traces 50 and 52 at once can double the speed at which refractive structures are written into the optical material 44. Similar effects may be obtained with the spaced focal spots 1074A, 1074B, ...1074N obtained in accordance with the present disclosure.

[0059] FIG. 7, for example, depicts a scan direction along the X coordinate axis parallel to a connecting line between the focal spots 40 and 42. Here, both working beams 20 and 22 trace overlapping paths for writing and rewriting the same traces 54 along each scanning path for such purposes as changing and further changing the refractive index of the optical material 44 along the traces 54. As shown in FIG. 7, each trace 54 is formed in a region where the traces 50 and 52, which are separately written by the respective focal spots 40 and 42, overlap along a common length. The traces 54 are spaced apart on center by an amount Ay corresponding to the amount each scan path is relatively indexed in the direction of the Y coordinate axis. The spatial offset As in the scan direction X results in a corresponding temporal offset between the respective interactions of the focal spots 40 and 42 with the optical material that depends upon the scanning speed. The corresponding temporal offset between the focal spots 40 and 42 allows heat generated by a lead focal spot, e.g., 40, to at least partially dissipate before the following focal spot, e.g., 42, generates additional heat at the same location within the optical material 44. For such purposes, the spatial offset As can be adjusted in relation to the scanning speed to maintain desired temperature profiles within the optical material 44. Similar effects may again be obtained by controlling the speed and direction of scanning of the spaced focal spots 1074A, 1074B, ...1074N obtained in accordance with the present disclosure.

[0060] The spatial offset As can be reduced to zero as shown in FIG. 8, and as described in WO2018/182946, while maintaining a desired temporal offset by At as shown in FIG. 4B to affect a nonsynchronous temporal spacing between pulses 30 and 32 and the overall doubling of the repetition rate. Here both working beams 20 and 22 converge to coincident focal spots 40 and 42 and contribute to forming the same set of traces 56 as traced by scan paths along the Y coordinate axis. The traces 56 are spaced on center by the index distance Ax between the scan paths. The optical path length difference between the working beams 20 and 22 can be adjusted to temporally offset the pulses 30 and 32 of the two working beams 20 and 22 through a time At as some fraction of the inverse of the repetition rate. When the pulses 30 and 32 are evenly spaced, the effect is temporally equivalent to doubling the repetition rate. However, when unevenly spaced, successive pairs of the pulses 30 and 32 can be delivered in groups within which the pulses 30 and 32 of each group are delivered in more rapid succession. If the pulses 30 and 32 within each group are spaced apart in the vicinity of the pulse width, the affect can be similar to enlarging the pulse width. However, at slightly larger temporal offsets At, the successive pulses 30 and 32 of each group can be used to further control energy transfer profiles within local volumes of the optical material 44. In addition, the relative amounts of pulse energy in the successive pulses 30 and 32 can be controlled, such as by changing the orientation of the half-wave plate 16, to further control the energy transfer profiles within the local volumes. For example, the energy transfer profiles can be set to both raise and maintain the accumulation of energy within the local volumes above the minimum threshold required for changing the refractive index of the optical material 44 and below the maximum threshold at which the intended optical performance of the optical material 44 is adversely affected. In this regard, the second of the successive pulses 30 and 32 within each group can be provided with less pulse energy than the first of the successive pulses 30 and 32 within each group to optimize the desired nonlinear absorption characteristics within the localized volumes of the optical material 44 without overheating or otherwise damaging the optical material 44. Similar effects may again be obtained for pairs of spaced focal spots 1074A, 1074B, ...1074N obtained in accordance with the present disclosure by employing at least two wedge sections in optical plate multiplexer 1051 which generate co-located but temporally separated focal spots, such as by employing flat wedge sections (so as not to diverge from the propagation axis of the source laser beam) of different thicknesses (so as to provide different time delays for pulses through the flat wedges).

[0061] FIG. 9 depicts a temperature profile within an optical material as a focal spot is scanned across the material from right to left. The temperature increases are more abrupt and concentrated at the leading edge of the focal spot and the resulting temperature gradients tend to persist and spread following the passage of the focal spot. Thus, the energy characteristics, e.g., pulse energy, pulse width, and repetition rate, as well as the spatial offset As and scan speed of a following focal spot must be arranged to account for any residual heat profiles in the optical material as a different base level to which the energy of the following focal spot is added. Similar considerations also apply when the spatial offset As includes a component that is traverse to the scanning direction.

[0062] An alternative beam multiplexer 60 is shown in FIG. 10, and as described in WO2018/182946, incorporating a focusing system for writing at multiple depths within an optical material. Various elements in common with the beam multiplexer 10 share the same reference numerals. For example, similar to the beam multiplexer 10, the laser source 12 outputs a collimated substantially linearly polarized beam 14, whose polarization axis is rotated by a half-wave plate 16 to a desired orientation with respect to the orthogonal polarization axes of a first polarization beamsplitter 18. The first polarization beamsplitter 18 divides the collimated output beam 14 into two orthogonally polarized working beams 62 and 64. Departures from a 45 degree orientation of the half-wave plate 16 can be used to adjust the relative pulse energies of the two working beams 62 and 64. The modulator 33 can be used to modulate the overall intensity of the output beam 14, and together with the adjustable half-wave plate 16 under the optional control of the controller 35, can adjust both the absolute and relative pulse energies of the two working beams 62 and 64.

[0063] The working beam 62, which has a first orthogonal polarization propagates directly to a second beamsplitter 28. Reflectors 24 and 26 direct the working beam 64, which has a second orthogonal polarization to the second beamsplitter 28. However, along the optical region between the reflectors 24 and 26, a beam shaping optic 66, which can take the form of a telescope, reshapes the working beam 64 from a substantially collimated form to a converging or diverting form. The amount of the divergence or convergence can be set manually or placed under the control of the controller 35.

[0064] A focusing system similar to the focusing system of FIG. 5 is also shown at the output of the second beamsplitter 28 and includes the reflector 36 and the objective lens 38. The reflector 36 is representative of the optical elements required to convey the collimated working beam 62 and the converging or diverging working beam 64 to the objective lens 38. For purposes of providing a clearer illustration, a break is provided between the reflector 36 and the objective lens 38 at which the working beam 62 is depicted as a collimated beam and the working beam 64 is depicted as a diverging beam approaching the objective lens 38. While also for purposes of illustration, the transverse dimension of the collimated working beam 62 is shown smaller than the traverse dimension of the diverging working beam 64, both working beams 62 and 64 may be sized to substantially fill the aperture of the objective lens 38.

[0065] The collimated working beam 62 is brought to focus at a focal spot 72 at the focal length of the objective lens 38. The diverging working beam 64 is brought to focus at a focal spot 74 that is located farther from the objective lens 38, which applies the same power of convergence too both working beams 62 and 64. The two focal spots 72 and 74 are located in transverse planes 73 and 75 that are spaced apart along the optical axis 68 of the objective lens 38 through a spatial offset Av. [0066] In a further embodiment of the present disclosure, a polarization multiplexing beam splitter system such as described above for Fig.10 and in WO2018/182946 generating two differentially polarized working beams 62 and 64 which are focused to different depths may be employed in combination with an optical plate beam multiplexer 1051 placed in the laser beam path after the two working beams 62 and 64 are aligned, such that the aligned working beams 62 and 64 are both divided by the wedge sections of the optical plate beam multiplexer, thereby forming two differentially polarized working laser beams at each wedge section which will be focused to different depths, resulting in two sets of working beams 1050A’, 1050B’, ...1050N’ (e.g., from working beam 62 divided by beam multiplexer 1051) and 1050A”, 1050B”, ...1050N” (from working beam 64 divided by beam multiplexer 1051) to effectively double the number of separated scanned focal spots obtainable with the optical plate beam multiplexer 1051 alone.

[0067] FIG. 11 is a greatly enlarged schematic depiction of the working beams 62 and 64 focused though focal spots 72 and 74 for writing lineartraces 76 and 78 at different depths along the Z coordinate axis within the optical material 44. A centerline spacing Az between the traces 76 and 78 corresponds to the spatial offset Av at which the working beams 62 and 64 are brought to focus through their respective focal spots 72 and 74. The traces 76 and 78 are shown scanned along the Y coordinate axis, and an array of linear trace pairs 76 and 78 can be formed by repeating the Y-axis scan at an index spacing Ax along the orthogonal X axis as shown for example in FIG. 8. When employed in combination with an optical plate multiplexer 1051 as described above, multiple sets of focal spots focused at different depths will be formed by each wedge section of the optical plate multiplexer.

[0068] The spacing Az corresponding to the spatial offset Av between the focal spots 72 and 74 can be set for writing contiguous layers of refractive index change or for writing different layers whose refractive index change is partially or completely independent of one another. The spatial offset Av in depth can be combined with other temporal and spatial offsets. For example, the focal spots 72 and 74 can be formed by pulses in their respective working beams 62 and 64 that are temporally offset by the time At so that the pulses (e.g., 30 and 32) of both working beams do not traverse the upper layer (e.g., trace 76) at exactly the same time as described in connection with FIG. 4B and FIG. 8. In addition, the focal spots 72 and 74 can also be spatially offset in the X-Y plane for further spatially separating the focal spots 72 and 74 in accordance with the spatial offset (e.g., As) and the relative direction at which the scan is taken relative to the X and Y coordinate axes as described in connection with FIG. 6 and for further temporally separating the focal spots in accordance with the spatial offset (e.g., As) and the scanning speed as described in connection with FIG. 7. The relative pulse energies of the working beams 62 and 64 can also be adjusted for such purposes as compensating for different purposes as compensating for different required writing parameters associated with writing at different depths. For instance, different spherical aberration plates would require different powers.

[0069] Depending on the selected offsets of the multiple scanned focal spots and the scanning direction, refractive index changes can be written in any combination of separate traces or contiguous regions within the optical material. In addition, the spatial offsets and scanning direction (and scanning speed) can be combined with temporal offsets as well as pulse energy distributions among the working beams to achieve and maintain energy profiles within the optical material at the marginal thresholds of the optical materials for undergoing localized refractive index changes without also undergoing breakdowns such as significant light scattering or absorption that degrade their intended performance.

[0070] Working beams can also be spatially offset by multifocal lens designs. Multiple focal lengths can be achieved by compound refractive or diffractive optics as well as by combinations of refraction and diffraction within the same optics. The amount of energy delivered to focal spots at different focal lengths can be controlled as well as the number of different focal spots at different focal lengths.

[0071] In addition to regulating the temporal and spatial offsets between different trains of pulses, the shape of pulses can also be controlled to improve writing performance in optical materials. For example, pulses can be elongated in their direction of propagation by various focusing techniques including the introduction of spherical aberration. Significantly, such pulse elongation can extend the volume of material within which individual focal spots can impart refractive index changes.

More optical power can be delivered within the extended volumes enabling a change in refractive index through a greater depth without exceeding the damage threshold of optical materials.

[0072] The graphs of FIGS. 12A and 12B and as described in WO2018/182946 compare exemplary plots of a change in phase Acp over a range of increasing average optical power Pavg for differently shaped pulses. The change in phase A(p is the desired temporal effect on the propagation of light through the optical material associated with the change in refractive index over an extended depth within the optical material 44. The change in phase Acp for a given wavelength is based on a product of the change in refractive index and the depth over which the index change is written (e.g., Acp = (2TT An d) / A; where An is the change in refractive index, d is the distance through which light travels through the changed refractive index material, and A is the wavelength of the light). Together, the product of the change in refractive index An and the physical distance d through which light travels through the changed refractive index material equals the optical path difference (OPD), which is the basis for the change in phase A(p experienced by light propagating through the optical material. Calibrated phase changes Acp can contribute to desired reshaping of wavefronts propagating through the optical material for contributing optical power or controlling optical aberrations. The average power P _avg can be calculated from the product of the pulse energy and the repetition rate (e.g., P _aV g = E _P R _ra te; where E _P is the energy per pulse and the Rrate is the repetition rate).

[0073] FIG. 12A shows a progressive increase in the change in phase Acp with the application of increasing average power Pavg delivered to an optical material within a conventional focal spot produced without significant spherical aberration or other focal spot elongation. At a certain average power P _avg , a damage threshold TD is reached at which the effect on phase change Acp becomes erratic. FIG. 12B shows that before the damage threshold TD is reached within a focal spot reshaped by spherical aberration or other focal spot elongation, additional average power P _avg can be delivered to the optical material to effect a further increase in the total change in phase Acp. That is, the elongated focal spot can receive more average power P _avg and effect a greater phase change Acp than a focal spot that is not similarly elongated. [0074] While the change in refractive index that can be effected by any one dose of actinic radiation in optical materials is limited by the damage thresholds of the materials, elongated focal spots can increase the change in phase supported by the change in refractive index by extending the change in refractive index through a greater depth. With conventionally formed focal spots, the change in refractive index is often too small to support 2TT phase changes, which are often needed to minimize phase discontinuities in Fresnel or other types of segmented optical structures written into the optical materials. However, by elongating the focal spots over extended depths, only one or at least fewer layers need to be written to effect 2TT phase changes. Thus, writing the refractive index changes over extended depths enables the faster and more accurate writing of such optical structures and can result in higher and more efficient optical performance.

[0075] A beam multiplexer arrangement 200 shown in FIG. 13 and as described in WO2018/182946 shares a number of components in common with the multiplexer arrangement 60 shown in FIG. 10 as indicated by their reference numerals in common. In addition to the components in common, the multiplexer arrangement 200 includes two beam shapers in the form of spherical aberration compensation plates 202 and 204 along the respective pathways of the two orthogonally polarized working beams 62 and 64 in locations at which the two beams 62 and 64 propagate in a substantially collimated form. However, instead of adding respective measures of spherical aberration to compensate for other unwanted sources of spherical aberration affecting the working beams 62 and 64, the spherical aberration compensation plates 202 and 204 introduce spherical aberration that remains wholly or at least partially uncorrected for producing elongated focal spots 206 and 208 in the optical material 44 in the direction of beam propagation. Both spherical aberration compensation plates 202 and 204 introduce positive spherical aberration or negative spherical aberration or one of the plates 202 or 204 can introduce positive spherical aberration and the other of the plates 202 or 204 can introduce negative spherical aberration. In addition, it is possible to introduce a combination of positive and negative spherical aberration. Alternatively, only one or the other spherical aberration compensation plates 202 or 204 can be used so that just one or the other of the focal spots 206 or 208 is elongated by spherical aberration. Such spherical aberration compensation plates are available from Edmund Optics Inc. of Barrington, New Jersey under the tradename TECHSPEC® Spherical Aberration Plate.

[0076] In the greatly enlarged axial view FIG. 14, the elongated focal spots 206 and 208 write linear traces 210 and 212 characterized by local changes in refractive index at different depths along the Z coordinate axis within the optical material 44. The centerline spacing Az between the traces 210 and 212 corresponds substantially to the spatial offset Av at which the working beams 62 and 64 are brought to focus through their respective focal spots 206 and 208. The traces 210 and 212 are shown scanned along the Y coordinate axis, and an array of linear trace pairs 210 and 212 can be formed by repeating the Y-axis scan at an index spacing Ax along the orthogonal X axis as shown for example in FIG. 5. When the features of FIG. 14 of WO2018/182946 are employed in combination with an optical plate multiplexer 51 similarly as described above with Fig. 8, multiple sets of elongated focal spots focused at different depths will be formed by each wedge section of the optical plate multiplexer. Alternatively, a spherical aberration compensation plate may be employed in the laser path of system of Figs. 1 and 2 of the present disclosure prior the optical plate multiplexer 1051 so as to obtain a single layer of multiple elongated focal spots corresponding to the wedge sections of optical plate multiplexer 1051 .

[0077] Also similar to other embodiments, the spacing Az corresponding to the spatial offset Av between the focal spots 206 and 208 can be set for writing contiguous layers of refractive index change or for writing different layers whose refractive index change is partially or completely independent of one another. The spatial offset Av in depth can be combined with other temporal and spatial offsets. For example, the focal spots 206 and 208 can be formed by pulses in their respective working beams 62 and 64 that are temporally offset by the time At so that their respective pulses do not traverse the upper layer (e.g., trace 210) at exactly the same time. In addition, the focal spots 206 and 208 can be spatially offset in the X- Y plane for further spatially separating the focal spots 206 and 208 in accordance with the spatial offset (e.g., As) and the relative direction at which the scan is taken relative to the X and Y coordinate axes as described in connection with FIG. 6. The focal spots 206 and 208 can be further temporally and spatially offset in accordance with the spatial offset (e.g., As) and the scanning speed as described in connection with FIG. 7. The relative pulse energies of the working beams 62 and 64 can also be adjusted for such purposes as compensating for different loses associated with writing at different depths.

[0078] However, in contrast to the preceding embodiments, the focal spots 206 and 208 are elongated along the Z axis as a result of the spherical aberration added to the working beams 62 and 64. The output power of the laser 12 transmitted by the working beams 62 and 64 may be increased as a function of the added spherical aberration so that the power received by the focal spots 206 and 208 remains above the nonlinear absorption threshold required to induce a desired change in the refractive index in the optical material 44 throughout at least a portion of the extended depths of focus while remaining below the breakdown threshold of the optical material 44. Preferably, the traces 210 and 212 are each written at a thickness T (corresponding to the elongated depth dimension of the focal spots 206 and 208) that is sufficient within the traces 210 and 212 individually or collectively to support a 2TT phase change for a nominal wavelength intended for propagation through the optical material 44. For example, at least one of the traces has a thickness T capable of supporting the 2TT phase change. Alternatively, the traces 210 and 212 as written in pairs of traces can have a combined thickness (e.g., 2T) capable of supporting the 2TT phase change. Either way, the collective focusing the working beams 62 and 64 result in the 2TT phase change as the objective lens 38 is relatively moved with respect to the optical material 44. For many vision systems, the nominal wavelength is expected to be around 550 nm, and a 0.02 index change would require a trace having a thickness of approximately 27.5 microns.

[0079] The shapes of focal spots, such as the focal spots 206 and 208, can be elongated in a plane of propagation, i.e. , in an axial plane by the introduction of positive or negative aberration. Positive spherical aberration tends to elongate the focal spots in a direction opposing the direction of propagation and negative spherical aberration tends to elongate the focal spots in the direction of propagation. That is, the added spherical aberration has the overall effect of shifting and reducing optical intensity at a peak focus while relatively increasing optical intensity in positions axially offset from the peak focus. Positive and negative spherical aberrations tend to shift the peak focus in opposite directions, which can be used to further control the depths and axial spacing at which the respective traces 210 and 201 are written. [0080] In FIG. 15 and as described in WO2018/182946, exemplary axial intensity distributions along the Z axis of focal spots are plotted for three different amounts of spherical aberration. The data is representative of an objective lens with a numerical aperture of 0.7 for conveying a 405 nm wavelength beam having a 6 mm beam diameter in a Gaussian form. Plot 220 represents an axial intensity distribution of a focal spot with no spherical aberration and appears as a conventional Gaussian focus centered at z = zero within the nominal focal plane. Plot 222, shown in dashed line, represents an axial intensity distribution of a focal spot exhibiting a first magnitude of negative spherical aberration (e.g., 2 microns of spherical aberration). Plot 224, shown in dotted line, represents an axial intensity distribution of a focal spot exhibiting a second higher magnitude of negative spherical aberration (e.g., 6 microns of spherical aberration). In general, the peaks of the intensity distributions tend to diminish and shift in a direction away from the light source as the magnitude of the negative spherical aberration increases. In addition, the intensity tends to distribute more widely through the depth of focus as spherical aberration becomes more pronounced.

[0081] An increase in optical power delivered to the extended depth focal spots not only restores the desired optical intensity near a peak focus for writing refractive index changes in the optical material 44 without inducing optical damage, the increase in optical power also elevates the intensities to either side of the peak focus above the nonlinear threshold for writing the desired refractive index changes throughout a greater depth of the optical material. By increasing the overall amount of optical power delivered to the elongated focal spots, the axial intensity distribution associated with a spherically aberrated focal spot can be elevated above the nonlinear absorption threshold TA over an extended depth while remaining below the damage threshold TD.

[0082] While the spherical aberration compensation plates 202 and 204 provide a ready way of introducing spherical aberration in collimated beams, a variety of other ways are known to introduce spherical aberration, including within converging or diverging beams. For example, simple plane parallel plates of varying optical thickness can be used in non-collimated beams to introduce varying amounts of spherical aberration by refracting marginal rays more than paraxial rays. Certain lenses are also available with corrector rings that can be used to adjust spherical aberration within the lenses.

[0083] In addition, while spherical aberration is an optical parameter that is relatively easy to control by beam shaping optics, a variety of other ways can be used to produce extended depth focal spots. For example, non-diffraction-limited beams, which generally focus to a larger spot size can also be arranged to expand along the depth of focus, i.e., in a paraxial approximation, as an expansion of the Rayleigh range from the beam waist to the point where the area of the beam cross section is doubled. For example, beam shapers of various types can be used including apodizers and diffractive optics.

[0084] The extended depth focal spots that are elongated in the direction of propagation are particularly useful for writing in ophthalmic materials with femtosecond lasers, particularly at high numerical apertures (e.g., above .28) and at high repetition rates (e.g., above 10 MHz). The extended depth focal spots allow for the more efficient use of optical power in ophthalmic materials where doses of laser radiation are limited for safety purposes. By writing over larger volumes within high numerical apertures at high speeds, the doses of laser power delivered to patients can be reduced.

[0085] Various types of single or multi-axis scanners can be incorporated into the refractive index writing systems of the present disclosure, such as scanners using angularly scanning rotating polygon mirrors or angularly scanned galvanometer- controlled mirrors such as described in Fig. 2, with image relaying systems to direct the working beams over appropriate pathways for writing refractive structures within an optical material.

[0086] FIG. 16 is a schematic diagram of an alternative scanning system employing optomechanical scanner 150 for writing refractive structures 152 within an optical material with stacked stages to provide for relatively moving a focusing system along three coordinate axes with respect to the optical material. The optomechanical scanner 150 includes a reciprocal shaker (e.g., a rapidly shaking impeller) as a fast axis scanner 154 that provides for rapidly translating an optics assembly 156 along a first scanning motion axis 158. The optics assembly 156 includes an objective lens similar to the objective lenses of the preceding embodiments for focusing working beams into an optical material. A high speed depth control stage and a spherical aberration correction stage can also be incorporated into the optics assembly 156. The high speed depth control can correct for angular motion errors to ensure and the spherical aberration stage can be used to correct for spherical aberrations to improve focal spot quality. One or more focal spots 151 of the working beams are directed along scan paths in the optical material as imparted by the optomechanical scanner 150.

[0087] The optomechanical scanner 150 also includes a motion stage 160 for translating both the optics assembly 156 and the fast axis scanner 154 along a second scanning motion axis 162, which is oriented orthogonal to the first scanning motion axis 158. The motion stage 160 can be arranged to provide continuous or stepped motions in synchronism with the motion imparted by the fast axis scanner 154. A precision height stage 164 is interposed between the motion stage 160 and the fast axis scanner 154 to raise and lower the fast axis scanner along a third scanning motion axis 166 for such purposes as controlling the depth at which the focal spots 151 are written into the optical material.

[0088] The optomechanical scanner 150 is particularly arranged for moving the optics assembly 156 with respect to the optical material, which can be particularly useful for in-vivo applications where the optical material cannot be as easily moved. However, for other applications or considerations, the motion axes can be distributed between the optics assembly 156 and the optical material in any combination, and one or more additional motion axes, including rotational axes, can be added as required.

[0089] The fast axis scanner 154 can be a commercial vibration exciter to provide high speed reciprocal motion. One example of such a commercial vibration exciter is a Bruel and Kjaer Measurement Exciter Type 4810 sold by Bruel & Kjaer Sound & Vibration Measurement A/S of Nagrum, Denmark. The motion stages 160 and 164 can be a high-precision linear stages, such as model GTS70 for lateral motion and model GTS20V for vertical motion from the Newport GTS Series, sold by Newport Corporation of Irvine, California and adapted via appropriate interface plates 170 and 172 for stacking the motion axes. [0090] Motions along the various axes 158, 162 and 164 can be controlled by an arrangement of controllers and amplifiers 174 that translate inputs 176 in the form of desired writing patterns into motions along the various axes 158, 162, and 164. For example, the fast axis scanner 154 can be controlled by an arbitrary waveform generator. Such waveform generators are sold by Agilent Technologies, Inc. of Santa Clara, California. The waveform for the motions along the first scanning motion axis 158 are arranged, for example, to result in the desired refractive index pattern along the first scanning motion axis 158. Instead of sending an arbitrary waveform to the fast axis scanner 154, a specially tuned sine wave can be sent to maximize performance. For example, the drive frequency can be tuned to a resonance frequency of the fast axis scanner 154 to enable high speed motion while inducing minimal disturbances into the supporting structures including the underlying motion stages 160 and 166.

[0091] The working beams 180 are aligned and steered along each axis of motion to ensure proper alignment of the working beams 180 with the optics assembly 156.

For example, a reflector 182 mounted on the interface plate 172 receives the working beams 180 in an orientation aligned with the motion axis 162 and redirects the working beams 180 in the direction of the motion axis 166 through an aperture 184 in the interface plate 170 to a reflector 186 that mounted together with the fast axis scanner 154 on the interface plate 170. The reflector 186 redirects the working beams 180 in the direction of the motion axis 158 above the fast axis scanner 154. Reflectors 188 and 190, which are also preferably mounted from the interface plate 170 redirect the working beams 180 within the same plane to a reflector 192, such as a fold prism, which aligns the working beams 180 with an optical axis 194 of the optics assembly 156.

[0092] Other types of single or multi-axis scanners can be incorporated, such as scanners using angularly scanning rotating polygon mirrors or angularly scanned galvanometer-controlled mirrors with image relaying systems to direct the working beams 180 over appropriate pathways for writing refractive structures 152 within an optical material.

[0093] The controllers and amplifiers 174 can also include a second synchronized arbitrary waveform generator for controlling a modulator 196, such as an electro- optic modulator or an acousto-optic modulator, for regulating the intensity of the working beams 180 in relation to motions along one or more of the motion axes 158, 162, and 166. For example, the beam intensity at the focal points 151 can be changed during a scan along the motion axis 15, or the beam intensity at the focal points can be reset to a new fixed value before each new trace is written. More integrated intensity control can be provided among the individual working beams including the distribution of pulse energy, as the working beams are moved along any combination of the motion axes 158, 162, and 166 to more fully regulate energy profiles within the optical material. The modulator 196, which can used to regulate the overall intensity or intensity distributions among the working beams is disposed in an optical path between a laser used for generating the working beams and a surface of the optical material. However, the modulator 196 is preferably located in advance of the beamsplitters for variably attenuating multiple working beams. The controller 35 of FIGS. 4A and 10 can also be incorporated among the controllers and amplifiers 174 to adjust one or more of the half-wave plate 16 of FIGS. 4A and 10, the delay element 34 of FIG. 4A, and the beam shaper of FIG. 10 for adjusting various parameters among the working beams 180.

[0094] Scanners such as the optomechanical scanner 150 can be arranged together with desired parameters for laser power, wavelength, and scan speed, to write millimeter-scale devices (e.g., up to about 8 mm wide) in the optical material at speeds exceeding 100 mm/sec. A lateral gradient index microlens can be written by changing the scanning speed after each trace is written, and/or by changing the laser intensity before the next trace is written. In addition, the index of refraction is changed by varying beam intensity or the scan speed along the length of a trace or by some combination of the two. Both positive lenses and negative lenses (as opposed to cylindrical lenses) can be written using a combination of overlapping lenses and synchronous intensity control. The overall refractive power can be tailored to the desired shape using these parameters, as well as global positioning and the laser modulator.

[0095] Further details of a useful scanning system are described in US Patent Application Publication No. 20160144580 A1 entitled HIGH NUMERICAL APERTURE OPTOMECHANICAL SCANNER FOR LAYERED GRADIENT INDEX MICROLENSES, METHODS, AND APPLICATIONS, which is hereby incorporated by reference. Exemplary suitable methods and techniques have been described, for example, in U.S. Pat. No. 7,789,910 B2, OPTICAL MATERIAL AND METHOD FOR MODIFYING THE REFRACTIVE INDEX, to Knox, et. al.; U.S. Pat. No. 8,337,553 B2, OPTICAL MATERIAL AND METHOD FOR MODIFYING THE REFRACTIVE INDEX, to Knox, et. al.; U.S. Pat. No. 8,486,055 B2, METHOD FOR MODIFYING THE REFRACTIVE INDEX OF OCULAR TISSUES, to Knox, et. al.; U.S. Pat. No. 8,512,320 B1 , METHOD FOR MODIFYING THE REFRACTIVE INDEX OF OCULAR TISSUES, to Knox, et. al.; and U.S. Pat. No. 8,617,147 B2, METHOD FOR MODIFYING THE REFRACTIVE INDEX OF OCULAR TISSUES. All of the above named patents, including the '910, '553, '055, '320, and '147 patents are incorporated herein by reference in their entirety for all purposes.

[0096] In exemplary embodiments, the laser source can be fashioned as mode- locked Ti:Sapphire laser (e.g., a Spectra-Physics TrSapphire oscillator such as MaiTai-HP available from Spectra-Physics, a Newport company, in Santa Clara, California) pumped by a frequency-doubled Nd:YVO4 laser. The laser can generate, for example, a succession of pulses of up to 3 W average power, a 110 fs pulse width, and an 80 MHz repetition rate or up to 1 W average power, a 160 fs pulse width and an 80 MHz repetition rate at around 400 nm frequency-doubled wavelengths. Of course, other lasers can be used or optimized for use with writing refractive index changes into different optical materials in accordance with the marginal thresholds of the materials for undergoing localized refractive index changes without also undergoing optically induced damage such as significant light scattering or absorption that degrade their intended performance. The optical materials include ophthalmic hydrogel polymers (used in contact lenses and intraocular lenses) and cornea tissue (both excised and in vivo) as well as other ophthalmic materials that are naturally occurring or synthetically produced.

[0097] It will be appreciated that variants of the above-disclosed and other features and functions, or alternatives thereof, may be combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.