Solid-state lasers are light amplifying devices designed to produce high intensity monochromatic light. Typical solid-state lasers include a pumping light source, an active material or medium (often called a laser rod, laser crystal, or lasant material), and a set of reflectors. Light from the pumping source produces stimulated emissions from specific atomic impurities (called dopants) in the active material and such emissions are caused to be amplified by resonation between a set of reflectors. The assembly including the active medium and reflectors makes up a laser resonator. The output properties of such a laser may be modified by the use of various host materials and/or combinations thereof (commonly, various types of glasses and crystals) and dopants as the active medium.

In certain applications it is useful to combine the outputs of two or more active media with dissimilar emission properties. In certain prior art devices two separate laser resonators are aligned so that the output of a first resonator is coupled into a second resonator thus producing a combined output. In other prior art arrangements the output beams of several resonators are combined by optical components such as lenses and mirrors to provide a single output beam. In other prior art arrangements, the properties of the output beam of a single resonator are modified using non-linear optics to contribute harmonic frequencies to the primary beam, thus producing a final output containing multiple wavelengths. These methods often require a tedious process of aligning the two or more resonators, or two or more beams, or two or more nonlinear optical elements, to optimize the performance of the system. Further, the modification of a primary beam using, e. g. nonlinear frequency doubling materials, restricts the output wavelengths to harmonics of the primary wavelength.

U. S. Patent 3,615,312 describes a method for combining two active media by a process of coaxial drawing of glassy materials in order to achieve an operatively unitary

laser device with combined output properties. Such a laser is a unitary device which operates as a single laser having a single resonant cavity.

One challenge of the prior art production of single resonators with two or more active media (recognized and addressed by the present invention) is the selection of reflector components that can produce optimal harmonic resonation in each portion of the combined medium.

U. S. Patent 5,432,811 discloses a technique for creating a resonant cavity within a laser rod by providing the rod with polyhedron shaped ends. The facets of these ends work as reflectors to produce resonant reflections within the rod, thus providing light amplification.

There has long been a need for a laser device capable of producing combined outputs of two or more laser active media without the need for complex alignment or expensive reflector design.

SUMMARY OF THE INVENTION The present invention, in one embodiment, discloses a laser with a resonator having a plurality of segments of laser media joined together into a single laser rod with polyhedral reflective ends. A conventional optical pumping source provides optical stimulus to the resonator. The resonator may be enclosed in a reflective tube and fitted with reflective end caps to enclose the resonator and hold it in place. Conventional cooling apparatus and techniques may be used to cool the resonator and pumping source.

Light from the pumping source is directed to and into the resonator material to stimulate photonic emissions from the various dopants. These emissions resonate within the laser rod between the reflective facets of the polyhedral ends. Stimulated emissions from each of the media segments is thereby caused to resonate, producing light amplification and emission from the resonator in a number of wavelengths corresponding to the primary emission wavelengths of each of the dopants in each segment.

In one particular embodiment, a first segment of laser medium such as Yttrium- Aluminum-Garnett (YAG) doped with neodymium (Nd: YAG) is joined to a second segment of laser medium doped with erbium (Er: YAG). The laser rod thus formed is ground and polished to produce a bihedral prism at each end. At one end of the rod a

short portion of the vertex of the bihedral prism is ground and polished to form a flat face orthogonal to the central axis of the rod, producing an output face (e. g. as in U. S. Patent 5,432,811).

Stimulated emissions produced in each segment of the rod by the introduction of pumping energy then resonate between the faceted ends and produce harmonic amplification as such emissions pass through the appropriate segment of the rod. The output of such a resonator consists of light at wavelengths corresponding to the primary emission wavelength of Nd: YAG (1064 nanometers) and Er: YAG (2940 nanometers).

Moreover the relative output energies at the two wavelengths are dependent on the relative efficiencies and volumes (i. e. segment lengths, when the cross sectional areas of the segments are equal) of the two laser media materials used in the rod. In other embodiments there are three, four, five, six or more joined segments of laser media. In other embodiments there are three, four, five or more facets on each polyhedron shaped.

Materials used to form the segments may be selected from the variety of known laser media, including, but not limited to, crystals and glasses doped with rare-earth elements.

The segments of laser media may be joined using several techniques. In one technique the ends of two segments are abutted at a joint and held in place with a ring around the circumference of the joint. This method may reduce the amount of lateral surface area available for pumping, and may reduce the efficiency of the system due to reflective losses produced by an air gap between the segments. In another method an adhesive cement is used (e. g., a high temperature epoxy) between the two segments (in one aspect in conjunction with the technique mentioned above). The adhesive, when cured, in certain embodiments has an index of refraction very close (in certain preferred embodiments within 10%) to that of the segments to be joined. Conditions of use should not be such that the thermal stresses produced by circulating energy in the rod cause the adhesive to fail. A third method includes abutting the two ends of the segments and heating the assembly to near the melting point of the two materials so that the segments are sintered together. This process is performed, in certain embodiments, under anaerobic conditions to prevent oxidation, and discoloration, of the materials. In another method of producing a laser rod with multiple segments of dissimilar doping, the addition of dopant materials is controlled during the crystal growth process. As a boule of crystal material is

grown, the type of dopant added to the growth chamber is changed producing a boule with two or more zones with differing chemical characteristics. A laser rod is cut from such a boule so that the rod contains several (two or more) differing segments.

In certain embodiments, a laser device with a laser according to the present invention emits a variety of laser wavelengths. Such a laser device is useful, inter alia, when the wavelengths are needed to produce different but essentially simultaneous effects in certain target materials. For example, one application of such a laser is in medical surgery where one wavelength is optimal for cutting tissue without excessive heat damage while a second wavelength is optimal for producing coagulation of blood to provide hemostasis. By incorporating known filtering optics into such a device, the emission wavelength (s) are selectable by a user.

In other embodiments, the efficiency of a laser is increased by providing staged amplification. If, for example, a suitable pumping source for a certain laser medium is not available, but a pumping source for a different material which produces an output wavelength capable of efficiently pumping the first medium is easily obtainable. Then a multimedia laser rod according to the present invention of both materials produces emission from one segment that stimulate emission from the other segment, thus producing the desired output.

In certain embodiments, the present invention discloses a solid state and/or multimedia laser with a faceted laser crystal resonator and an output window ground and polished to a curved surface, to either focus or de-focus a laser beam as it emerges from the crystal resonator. This reduces the need for external focusing optics and increases the ruggedness and cost effectiveness of solid state lasers employing crystal resonators.

The present invention, in certain embodiments, discloses an active laser element with at least two segments of dissimilar active laser media joined together forming a columnar laser rod having a first end, and a second end spaced apart from the first end, each media having a primary emission wavelength, the first end shaped for internally reflecting light therefrom, the second end shaped for internally reflecting light therefrom, and the two segments of dissimilar active laser media disposed so that optical stimulation thereof produces amplified light from the columnar laser rod in wavelengths corresponding to the primary emission wavelengths of the media; such an active laser

element wherein the first end is shaped as a non-emissive prism with at least two sides; such an active laser element wherein the second end has an exit window portion (in one aspect with a curved portion to focus or defocus an output laser beam) for the exit of an output laser beam from the columnar laser rod; such an active laser element wherein the columnar laser rod has a cross sectional area and the exit window portion has a cross sectional area, the cross sectional area of the window being about five percent to about seventy-five percent of the cross sectional area of the rod; such an active laser element wherein the second end is shaped as a non-emissive prism with at least two sides. The present invention, in certain embodiments, discloses an active laser element with at least two segments of dissimilar active laser media joined together forming a columnar laser rod having a first end, and a second end spaced apart from the first end, each media having a primary emission wavelength, the first end shaped for internally reflecting light therefrom and shaped as a non-emissive prism with at least two sides, the second end having an exit window portion for exit of an output laser beam and shaped for internally reflecting light therefrom and shaped as a non-emissive prism with at least two sides, the two segments of dissimilar active laser media disposed so that optical stimulation thereof produces amplified light from the columnar laser rod in wavelengths corresponding to the primary emission wavelengths of the media, and the columnar laser rod having a cross sectional area and the exit window portion having a cross sectional area, the cross sectional area of the window being about five percent to about seventy-five percent of the cross sectional area of the rod.

The present invention, in certain embodiments, discloses an active laser element with at least two segments of dissimilar active laser media joined together forming a columnar laser rod having a first end, and a second end spaced apart from the first end, each media having a primary emission wavelength, the first end shaped for internally reflecting light therefrom, the second end shaped for internally reflecting light therefrom, the two segments of dissimilar active laser media disposed so that optical stimulation thereof produces amplified light from the columnar laser rod in wavelengths corresponding to the primary emission wavelengths of the media, and the second end having an exit window with a curved portion, the exit window for exit of an output laser beam from the columnar laser rod.

The present invention, in certain embodiments, discloses a laser resonator with a columnar laser rod having a first end, and a second end spaced apart from the first end, the first end shaped for internally reflecting light therefrom, the first end shaped as a non- emissive prism with at least two sides, the second end shaped for internally reflecting light therefrom and having an exit window portion for the exit of an output laser beam from the columnar laser rod, and the exit window of the second end having a curved surface; such a laser resonator wherein the curved surface focuses the output laser beam; and such a laser resonator wherein the curved surface defocuses the output laser beam.

The present invention discloses, in certain embodiments, a laser with a pumping light source, a cooling apparatus, and an active laser element with at least two segments of dissimilar active laser media joined together forming a columnar laser rod having a first end, and a second end spaced apart from the first end, each media having a primary emission wavelength, the first end shaped for internally reflecting light therefrom, the second end shaped for internally reflecting light therefrom, and the two segments of dissimilar active laser media disposed so that optical stimulation thereof produces amplified light from the columnar laser rod in wavelengths corresponding to the primary emission wavelengths of the media.

Certain embodiments of this invention are not limited to any particular individual feature disclosed here, but include combinations of such features distinguished from the prior art in their structures and functions. Features of the invention are broadly described so that the detailed descriptions that follow may be better understood, and in order that the contributions of this invention to the arts may be better appreciated. There are, of course, additional aspects of the invention described herein and which may be in the subject matter of the claims to this invention. Those skilled in the art who have the benefit of this invention, its teachings, and suggestions will appreciate that the conceptions of this disclosure may be used as a creative basis for designing other structures, methods and systems for carrying out and practicing the present invention. The claims of this invention are to be read to include any legally equivalent devices or methods which do not depart from the spirit and scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention recognizes and addresses the previously mentioned problems and long felt needs and provides a solution to those problems and satisfactory meeting of those needs in its various possible embodiments and equivalents thereof. To one of skill in this art who has the benefits of this invention's realizations, teachings, disclosures, and suggestions, other purposes and advantages will be appreciated from the following description of preferred embodiments, given for the purpose of disclosure, when taken in conjunction with the accompanying drawings. The detail in these descriptions is not intended to thwart this patent's object to claim this invention no matter how others may later disguise it by variations in form or additions of further improvements.

Fig. 1A is a schematic view of a resonator system in accordance with the present invention. Figs. 1B and 1C show end views of the system of Fig. 1A.

Fig. 2A is a schematic view of a resonator system in accordance with the present invention. Figs. 2B and 2C show end views of the system of Fig. 2A.

Fig. 3A is a schematic view of a resonator system in accordance with the present invention. Figs. 3B and 3C show end views of the system of Fig. 3A.

Fig. 4A is a schematic view of a resonator system in accordance with the present invention. Figs. 4B and 4C show end views of the system of Fig. 4A.

Fig. SA is a schematic view of a resonator system in accordance with the present invention. Figs. 5B and 5C show end views of the system of Fig. 5A. Fig. 5D is an enlarged view of a portion of a resonator system of Fig. 5A.

Fig. 6 is a photograph of a resonator in accordance with the present invention with segments joined by controlled doping of the crystal.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Figs. lA-1C, an active laser element 10 has a first segment 12 of laser medium material abutted against a second segment 14 of a different laser medium material, each with a primary emission wavelength. The two pieces form a single column of active laser material with a front end 16 and a rear end 18. Reflecting facets 20 on the rear end 18 are, preferably, ground and polished on each end forming a vertex. The tip of

the output face of the end 16 is, preferably, ground and polished to form reflecting facets 22 and an output window 24.

Figs. 2A-2C show an active laser element 30 with first and second segments 32 and 34 of different laser active material joined together with a collar ring 9. Rear end 37 and front end 38 are ground and polished to form reflecting dihedral facets, with the vertex of the front end 38 ground and polished to form an output window 35.

Figs. 3A-3C show an active laser element 50 with three segments of different laser active media 51,52, and 53 joined by adhesive cement at joints 54. Terminal ends of the rod thus formed are ground and polished to create reflecting facets at ends 55 and 56. A vertex of the front end 56 is, preferably, ground and polished to form an output window 57.

Figs. 4A-4C show a laser active element 60 in accordance with the present invention having segments 61 and 62 which are grown as one piece during a crystal growth process by changing the nature and amount of dopant added to the growth medium (e. g., but not limited to, a crystal grown from YAG doped with the addition of trace amounts of erbium for some period and then the dopant is either gradually or abruptly switched to neodymium). A transition zone 64 between regions the segments 61 and 62 may contain different dopants. In one aspect, this region is an abrupt transition from a concentration of the first dopant to a concentration of the second; or, alternatively, the transition zone may have a gradual concentration gradient.

Figs. 5A-5C show a crystal resonator 100 according to the present invention with polyhedral shaped ends 102,103 (see also U. S. Patent 5,432,811). An output window portion 104 of the resonator 100 is shown to be curved to form an integrated lens 106 which produces focusing of an output beam from the resonator 100. In another aspect the end is shaped to defocus the output beam. Fig. 5B shows an enlarged view of the curved output window 104.

Fig. 6 shows a laser crystal resonator 120 according to the present invention with a segment 122 joined to segment 124 by controlled doping as described above.

In conclusion, therefore, it is seen that the present invention and the embodiments disclosed herein and those covered by the appended claims are well adapted to carry out the objectives and obtain the ends set forth. Certain changes can be made in the subject

matter without departing form the spirit and the scope of this invention. It is realized that changes are possible within the scope of this invention and it is further intended that each element or step recited in any of the following claims is to be understood as referring to all equivalent elements or steps. The following claims are intended to cover the invention as broadly as legally possible in whatever form it may be utilized. The invention claimed herein is new and novel in accordance with 35 U. S. C. § 102 and satisfies the conditions for patentability in § 102. The invention claimed herein is not obvious in accordance with 35 U. S. C. § 103 and satisfies the conditions for patentablility in § 103. This specification and the claims that follow are in accordance with all of the requirements of 35 U. S. C. § 112.