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Title:
AN INTERFEROMETRIC MICROSCOPY TECHNIQUE FOR INSPECTING A SAMPLE SIMULTANEOUSLY AT DIFFERENT DEPTHS OF THE SAMPLE
Document Type and Number:
WIPO Patent Application WO/2017/041840
Kind Code:
A1
Abstract:
An interferometric microscopy arrangement for inspecting a sample simultaneously along different depths of the sample is presented. The arrangement includes an interferometric unit and a sensor assembly. The interferometric unit generates an object beam and a reference beam. The sensor assembly includes a primary beam splitter and a plurality of sensors having a first sensor and a second sensor located at different positions with respect to the primary beam splitter. The interferometric unit directs the object beam and the reference beam to form an interference pattern forming beam directed towards the sensor assembly. The primary beam splitter of the sensor assembly receives and splits the interference pattern forming beam into at least a first and a second part. The primary beam splitter then directs the first part towards the first sensor and the second part towards the second sensor.

Inventors:
HAYDEN OLIVER (DE)
SCHICK ANTON (DE)
SCHMIDT OLIVER (DE)
Application Number:
PCT/EP2015/070626
Publication Date:
March 16, 2017
Filing Date:
September 09, 2015
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
SIEMENS HEALTHCARE GMBH (DE)
International Classes:
G02B21/14; G01B9/02; G02B21/36; G02B27/14
Domestic Patent References:
WO2013053822A12013-04-18
WO2013140396A12013-09-26
Foreign References:
US20130070251A12013-03-21
US6172349B12001-01-09
Other References:
None
Download PDF:
Claims:
Patent claims

1. An interferometric microscopy arrangement (1) for inspect¬ ing a sample (2) simultaneously along different depths of the sample (2), the sample (2) to be inspected being probed by a probing light beam (10) incident on the sample (2), the interferometric microscopy arrangement (1) comprising:

- an interferometric unit (30) configured to generate an ob- ject beam (32) and a reference beam (34); and

- a sensor assembly (40) comprising a primary beam splitter (50) and a plurality of sensors (70, 80), wherein the plural¬ ity of sensors (70, 80) includes at least a first sensor (70) and a second sensor (80), and wherein at least the first sen¬ sor (70) and the second sensor (80) are located at different positions with respect to the primary beam splitter (60); and wherein interferometric unit (30) is further configured to direct the object beam (32) and the reference beam (34) form¬ ing an interference pattern forming beam (35) directed to¬ wards the sensor assembly (40), and wherein the primary beam splitter (50) of the sensor assembly (40) is further configured to receive the interference pat¬ tern forming beam (35) and to split the interference pattern forming beam (35) into at least a first part (37) and a se¬ cond part (38) and to direct the first part (37) of the in¬ terference pattern forming beam (35) towards the first sensor (70) and to direct the second part (38) of the interference pattern forming beam (35) towards the second sensor (80) .

2. The interferometric microscopy arrangement (1) according to claim 1, wherein the sensors (70, 80) in the sensor assem- bly (40) are organized in a staggered arrangement.

3. The interferometric microscopy arrangement (1) according to claim 1 or 2, wherein the first sensor (70) is positioned at a first distance (51) from the primary beam splitter (50) and the second sensor (80) is positioned at a second distance (52) from the primary beam splitter (50), and wherein the first distance (51) is different from the second distance (52) .

4. The interferometric microscopy arrangement according to claim 3, wherein at least one of the first sensor (70), the second sensor (80) and the primary beam splitter (50) is mov- able such that the first distance (51) and/or the second dis¬ tance (52) is changeable.

5. The interferometric microscopy arrangement (1) according to claim 3 or 4, wherein difference between the first dis- tance (51) and the second distance (52) corresponds to one of a depth of field value of the interferometric microscopy ar¬ rangement (1), a product of multiplication of a depth of field value of the interferometric microscopy arrangement (1) with a magnification factor of the interferometric microscopy arrangement (1), and a product of multiplication of a depth of field value of the interferometric microscopy arrangement (1) with a square of a magnification value of the

interferometric microscopy arrangement (1). 6. The interferometric microscopy arrangement (1) according to any of claims 1 to 5, wherein the sensor assembly (40) in¬ cludes a first sub-assembly (41) comprising one or more first beam splitters (71, 73) and a corresponding number of first additional sensors (72, 74), wherein the one or more first beam splitters (71, 73) are configured to sequentially split the first part (37) of the interference pattern forming beam (35) and wherein each of the one or more first beam splitters (71, 73) is located at a different position with respect to the primary beam splitter (50) and is configured to direct different sections of the first part (37) of the interfer¬ ence pattern forming beam (35) to two corresponding first additional sensor (72, 74) .

7. The interferometric microscopy arrangement (1) according to claim 6, wherein the first additional sensors (72, 74) in the first sub-assembly (41) are organized in a staggered ar¬ rangement .

8. The interferometric microscopy arrangement (1) according to claim 6 or 7, wherein in the first sub-assembly (41) dis¬ tance between a selected first beam splitter (71, 73) and one of the first additional sensor (72, 74) corresponding to the selected first beam splitter (71, 73) is different from dis¬ tance between the selected first beam splitter (71, 73) and another of the first additional sensor (72, 74) corresponding to the selected first beam splitter (71, 73) . 9. The interferometric microscopy arrangement (1) according to claim 8, wherein difference between the distances corre¬ sponds to one of a depth of field value of the

interferometric microscopy arrangement (1), a product of mul¬ tiplication of a depth of field value of the interferometric microscopy arrangement (1) with a magnification factor of the interferometric microscopy arrangement (1), and a product of multiplication of a depth of field value of the

interferometric microscopy arrangement (1) with a square of a magnification value of the interferometric microscopy ar- rangement (1) .

10. The interferometric microscopy arrangement (1) according to claim 9, wherein at least one of the first beam splitters (71, 73) and the two first additional sensors (72, 74) corre- sponding to the first beam splitter (71, 73) is movable such that the difference between the distances is changeable.

11. The interferometric microscopy arrangement (1) according to any of claims 1 to 10, wherein the sensor assembly (40) includes a second sub-assembly (42) comprising one or more second beam splitters (81, 83, 85) and a corresponding number of second additional sensors (82, 84, 86), wherein the one or more second beam splitters (81, 83, 85) are configured to se- quentially split the second part (38) of the interference pattern forming beam (35) and wherein each of the one or more second beam splitters (81, 83, 85) is located at a different position with respect to the primary beam splitter (50) and is configured to direct different sections of the second part (38) of the interference pattern forming beam (35) to two corresponding second additional sensor (82, 84, 86).

12. The interferometric microscopy arrangement according to claim 11, wherein the second additional sensors (82, 84, 86) in the second sub-assembly (42) are organized in a staggered arrangement .

13. The interferometric microscopy arrangement (1) according to claim 11 or 12, wherein in the second sub-assembly (42) distance between a selected second beam splitter (81, 83, 85) and one of the second additional sensor (82, 84, 86) corre¬ sponding to the selected second beam splitter (81, 83, 85) is different from distance between the selected second beam splitter (81, 83, 85) and another of the second additional sensor (82, 84, 86) corresponding to the selected second beam splitter (81, 83, 85) .

14. The interferometric microscopy arrangement (1) according to claim 13, wherein difference between the distances corre¬ sponds to one of a depth of field value of the

interferometric microscopy arrangement (1), a product of mul¬ tiplication of a depth of field value of the interferometric microscopy arrangement (1) with a magnification factor of the interferometric microscopy arrangement (1), and a product of multiplication of a depth of field value of the

interferometric microscopy arrangement (1) with a square of a magnification value of the interferometric microscopy ar¬ rangement ( 1 ) .

15. The interferometric microscopy arrangement (1) according to claim 14, wherein at least one of the second beam split¬ ters (81, 83, 85) and the two second additional sensors (82, 84, 86) corresponding to the second beam splitter (81, 83, 85) is movable such that the difference between the distances is changeable. 16. The interferometric microscopy arrangement (1) according to any of claims 1 to 15, wherein interferometric unit (30) comprises :

- an incident light beam splitter (11) configured to receive the probing light beam (10) before the probing light beam

(10) is incident on the sample (2), to generate the object beam (32) and the reference beam (34) by splitting the prob¬ ing light beam (10), and to direct the object beam (32) to¬ wards the sample (2) and to direct the reference beam (34) away from the sample (2) such that the reference beam (34) is not incident on the sample (2);

- a microscope objective unit (20) configured to receive the object beam (32) after the object beam (32) has interacted with the sample (2); and

- an optical setup (90) configured to receive the object beam (32) from the microscope objective unit (20) and the refer¬ ence beam (34) from the incident light beam splitter (11), wherein the optical setup (90) is further configured to com¬ bine the object beam (32) so received and the reference beam

(34) so received to form the interference pattern forming beam (35) and to direct the interference pattern forming beam

(35) towards the sensor assembly (40).

17. The interferometric microscopy arrangement (1) according to any of claims 1 to 15, further comprising:

- a microscope objective unit (20) configured to receive the probing light beam (10) after the probing light beam (10) has interacted with the sample (2); and - wherein the interferometric unit (30) is configured to de¬ fine an object beam path to direct the object beam (32) to¬ wards the sensor assembly (40) and a reference beam path to direct the reference beam (34) towards the sensor assembly (40) and wherein the object beam path substantially overlaps with the reference beam path, the interferometric unit (30) comprising :

- an interferometric unit beam splitter/combiner (33) config- ured to receive the probing light beam (10) from the micro¬ scope objective unit (20) and to split the probing light beam (10) so received into the object beam (32) and the reference beam ( 34 ) ; - an object beam reflector (102) positioned in the object beam path and configured to receive the object beam (32) from the interferometric unit beam splitter/combiner (33) and to reflect the object beam (32) back towards the interferometric unit beam splitter/combiner (33), and wherein the

interferometric unit beam splitter/combiner (33) is further configured to direct the object beam (32) reflected back from the object beam reflector (102) towards the sensor assembly (40) ; - a reference beam reflector (104) positioned in the refer¬ ence beam path and configured to receive the reference beam (34) from the interferometric unit beam splitter/combiner (33) and to reflect the reference beam (34) back towards the interferometric unit beam splitter/combiner (33), and wherein the interferometric unit beam splitter/combiner (33) is fur¬ ther configured to direct the reference beam (34) reflected back from the reference beam reflector (104) towards the sensor assembly (40); - a spatial filter (66) positioned optically in front of the reference beam reflector (104) and configured to at least partially filter object information from the reference beam (34) before the reference beam (34) is reflected back from the reference beam reflector (104); and

- a reference beam Fourier optics assembly comprising at least a first lens (64) arranged at 4f configuration to a se¬ cond lens (24 ) .

18. The interferometric microscopy arrangement (1) according to claim 17, wherein the spatial filter (66) is a pinhole.

19. An interferometric microscopy method (1000) for inspect¬ ing a sample (2) simultaneously along different depths of the sample (2) by inspecting the sample (2) by an interferometric microscopy device, the sample (2) to be inspected being probed by a probing light beam (10) incident on the sample

(2), the interferometric microscopy method (1000) comprising:

- generating (200) an object beam and a reference beam by an interferometric unit (30);

- providing (300) a sensor assembly (40) comprising a primary beam splitter (50) and a plurality of sensors (70, 80), wherein the plurality of sensors (70, 80) includes at least a first sensor (70) and a second sensor (80), and wherein at least the first sensor (70) and the second sensor (80) are located at different positions with respect to the primary beam splitter (50);

- directing (400) the object beam (32) and the reference beam (34) to form an interference pattern forming beam (35) directed towards the sensor assembly (40);

- receiving (500) the interference pattern forming beam (35) by the primary beam splitter (50) of the sensor assembly (40); - splitting (600), by the primary beam splitter (50), the interference pattern forming beam (35) into at least a first part (37) and a second part (38); - directing (700) the first part (37) of the interference pattern forming beam (35) towards the first sensor (70) and the second part (38) of the interference pattern forming beam (35) towards the second sensor (80); and -determining (800) a first interference pattern at the first sensor (70) and a second interference pattern at the second sensor (80).

20. The interferometric microscopy method (1000) according to claim 19, further comprising combining (900) the first interference pattern and the second interference pattern to form a combined interference pattern.

21. The interferometric microscopy method (1000) according to claim 19 or 20, wherein the sensors (70, 80) in the sensor assembly (40) are organized in a staggered arrangement.

22. The interferometric microscopy method (1000) according to any of claims 19 to 21, wherein the first sensor (70) is po- sitioned at a first distance (51) from the primary beam splitter (50) and the second sensor (80) is positioned at a second distance (52) from the primary beam splitter (50), and wherein the first distance (51) is different from the second distance ( 52 ) .

23. The interferometric microscopy method (1000) according to claim 22, wherein difference between the first distance (51) and the second distance (52) corresponds to one of a depth of field value of the interferometric microscopy device, a prod- uct of multiplication of a depth of field value of the interferometric microscopy device with a magnification factor of the interferometric microscopy device, and a product of multiplication of a depth of field value of the interf erometric microscopy device with a square of a magnifi¬ cation value of the interf erometric microscopy device.

Description:
Description

An interferometric microscopy technique for inspecting a sam ¬ ple simultaneously at different depths of the sample

The present invention relates to interferometric techniques, and more particularly to an interferometric microscopy ar ¬ rangement and an interferometric microscopy method for in ¬ specting a sample simultaneously at different depths of the sample.

Medical technology in recent times has witnessed advent of numerous medical devices and microscopy techniques. A lot of these microscopy techniques are used for imaging microscopic specimens or samples by detecting and analyzing interference patterns formed by superimposition of an object beam and a reference beam for example Interferometric microscopy, also referred to as Digital holographic microscopy (DHM) . Broadly, interferometric microscopy is classified as common path in- terferometry or different path interferometry .

In common path interferometry, a light beam is shone or impinged on a sample to be inspected and then the light beam emerging after interacting with the sample or specimen is split into a reference beam and an object beam. Subsequently, object information is filtered out or deleted from the refer ¬ ence beam and then the filtered reference beam is superim ¬ posed with the object beam to detect the interference pattern to be studied. In different path interferometry, a light beam to be incident on the sample is first split into an object beam and a reference beam i.e. the light beam is split into the reference beam and the object beam before interacting with the sample. The object beam is then shone or impinged upon the sample but the reference beam is directed to another optical path within the interferometric unit and is not shone or impinged upon the sample. Subsequently, the object beam carrying object information is superimposed with the reference beam to obtain interference pattern. The interference pattern obtained as an output of the common path or different path interferometry is analyzed. The interference pattern al ¬ so referred to as image of the sample represents characteris ¬ tics of the sample such as physical structures in the sample, density of the sample, and so on and so forth.

The presently known interferometric microscopic technique is well suited for samples that spread along a lateral plane, i.e. XY plane substantially perpendicular to a direction of the incoming beam incident on the sample, because the image or the interference pattern obtained as an output of the interferometric microscopic technique is focused along this lateral plane of the sample. In case where the sample extends also in depth i.e. in Z direction with respect to this XY plane, although the interference pattern obtained includes information coming along from different depths of the sample, but segments of the image or the interference pattern coming from different depths of the sample other than this XY plane are not in focus i.e. the sharpness of segments of the inter ¬ ference pattern representing the sample parts at these other depths is low or not of acceptable quality or blurred.

To explain further, an image or interference pattern of a three dimensional sample can be understood or imagined as a stack of several XY planes, each XY plane also having a thickness, i.e. extending in the Z direction, equivalent to a depth of field for the imaging system, i.e. the

interferometric microscopic device, used to acquire the image or the interference pattern. The interferometric microscopic device used for imaging the sample is however effectively fo ¬ cused on one of these several XY planes and sections or seg ¬ ments of the interference pattern from those parts of the sample which are represented in this XY plane are sharp or in focus, and also immediately adjacent parts of the sample rep- resented in the interference pattern around this XY plane, depending on the depth of field, are in acceptable focus to construe or interpret desired information from the sample. However, other parts of the sample that are not in this XY plane and in the region around this XY plane, taking into ac ¬ count the depth of field, are out-of-focus i.e. the segments of the image or the interference pattern representing these other parts of the sample are not sharp enough or focused enough for desired use, such as to visualize fine structures or to construct accurate morphology of a micro-entity such as a cell or a red blood cell in the sample.

One way of viewing such sample having depth, i.e. the sample extending in Z direction is to adjust the focus of the interferometric microscopic device between consecutive images in order to bring into focus different segments of the image representing different depths of the sample. However, this approach has at least two major drawbacks.

Firstly, although a given depth of the sample can be brought in focus by readjusting the focus of the interferometric mi ¬ croscopic device but at a given instance of time only parts of sample extending along one lateral plane at a given depth are in focus, i.e. different parts of the sample extending along two different lateral planes at different depths of the sample are not simultaneously in focus.

Secondly, for samples those are in flow, for example samples in a flow cell or passing through a flow channel as are being imaged, are dynamic so there is no time to adjust the focus of the interferometric microscopic device. Furthermore, for samples those are in flow, readjusting the focus of the interferometric microscopic device will essentially mean lapse of sometime between two consecutive images and since the sample is in flow, some sample characteristics for exam ¬ ple a position of a cell in the flow will change between the two consecutive images acquired at different points in time. Some interferometric microscopic device used for imaging sam- pies in flow try to align the sample, for example by using sheath flow techniques, in a desired region inside the flow chamber or flow cell such that the sample is maintained in the focus, however, such techniques to align the sample in flow are not full proof, highly complex and require sophisti ¬ cated flow setups.

Thus the object of the present disclosure is to provide a technique for improving present day interferometric devices and setups, more particularly for simultaneously inspecting a sample at different depths of the sample such that parts of the sample at different depths are imaged with focus or with an acceptable sharpness.

The above object is achieved by an interferometric microscopy arrangement for inspecting a sample simultaneously at differ ¬ ent depths of the sample according to claim 1 and an

interferometric microscopy method for inspecting a sample simultaneously at different depths of the sample according to claim 19. Advantageous embodiments of the present technique are provided in dependent claims. Features of independent can be combined with features of dependent claims, and features of dependent claims can be combined together.

An aspect of the present technique presents an

interferometric microscopy arrangement, hereinafter the ar ¬ rangement, for inspecting a sample simultaneously along dif ¬ ferent depths of the sample. The sample to be inspected is to be probed by a probing light beam incident on the sample. The arrangement includes an interferometric unit and a sensor as ¬ sembly. The interferometric unit, hereinafter the unit, gen ¬ erates an object beam and a reference beam. The sensor assem ¬ bly includes a primary beam splitter and a plurality of sen- sors . The plurality of sensors includes at least a first sen ¬ sor and a second sensor. The first sensor and the second sen ¬ sor are located at different positions with respect to the primary beam splitter. The unit directs the object beam and the reference beam to form an interference pattern forming beam directed towards the sensor assembly. The primary beam splitter of the sensor assembly receives the interference pattern forming beam and splits the interference pattern forming beam into at least a first and a second part. The primary beam splitter then directs the first part of the interference pattern forming beam towards the first sensor and the second part of the interference pattern forming beam to ¬ wards the second sensor. The differently located sensors form interference patterns that are focused on a different depth of the sample, or to say focused on a different lateral plane when viewed in a direction from the incident beam path towards the sample.

The sample may be understood as a stack of different lateral planes when viewed in a direction that is same as the direc ¬ tion of the probing light beam, and with this method parts of the sample present at least in two of the different lateral planes out of the stack are imaged in form of distinct inter ¬ ference patterns formed on the different sensors of the sen ¬ sor assembly, meaning thereby that the interference pattern formed at the first sensor with focus determines a part of the sample aligned along a first lateral plane out of the stack and the interference pattern formed at the second sen ¬ sor determines with focus another part of the sample aligned along a second lateral plane out of the stack. Thus parts of the sample aligned at the first and the second lateral planes out of the stack are imaged or determined with focus and thus high quality image or high quality interference pattern of the sample is obtained compared to an image or an interfer ¬ ence pattern of the sample obtained by an interferometric mi ¬ croscopy device or arrangement not having the sensor assembly of the present technique. In an embodiment of the arrangement, the sensors in the sen ¬ sor assembly are organized in a staggered arrangement. This provides a suitable arrangement to direct the parts of the interference pattern forming beam towards the different sen ¬ sors by simple setup of beam splitters.

In another embodiment of the arrangement, the first sensor is positioned at a first distance from the primary beam splitter and the second sensor is positioned at a second distance from the primary beam splitter. The first distance is different from the second distance. Thus two pre-selected depths in the sample may be inspected with focus. In another embodiment of the arrangement, at least one of the first sensor, the second sensor and the primary beam splitter is movable such that the first distance and/or the second distance are changeable. Thus one or more parts of the sample may be voluntarily brought in focus for a given sensor.

In another embodiment of the arrangement, difference between the first distance and the second distance corresponds to one of a depth of field value of the arrangement, a product of multiplication of a depth of field value of the arrangement with a magnification factor of the arrangement, and a product of multiplication of a depth of field value of the arrange ¬ ment with a square of a magnification value of the arrange ¬ ment. This provides possible ways of organizing the sensors in the sensor assembly to image or inspect with focus differ- ent preselected parts of the sample. In certain embodiments, the difference between the first and the second distance is such that the lateral planes that are imaged with focus form a continuous sequence taking into consideration the depth of field of the arrangement at the lateral planes in the sample.

In another embodiment of the arrangement, the sensor assembly includes a first sub-assembly. The first sub-assembly in ¬ cludes one or more first beam splitters and a corresponding number of first additional sensors. The one or more first beam splitters are configured to sequentially split the first part of the interference pattern forming beam. Each of the one or more first beam splitters is located at a different position with respect to the primary beam splitter. Each of the one or more first beam splitters is configured to direct different sections of the first part of the interference pat ¬ tern forming beam to two corresponding first additional sensor. This provides to obtain multiple independent interfer ¬ ence patterns at the different sensors of the first sub- assembly wherein each such interference pattern provides a focused image for a different depth in the sample or to say different lateral plane in the sample. The different lateral planes are perpendicular to a direction of the probing light beam incident on the sample.

In another embodiment of the arrangement, the first addition ¬ al sensors in the first sub-assembly are organized in a stag ¬ gered arrangement. This provides a suitable arrangement to direct the parts of the interference pattern forming beam to ¬ wards the different sensors by simple setup of beam split ¬ ters .

In another embodiment of the arrangement, in the first sub- assembly distance between a selected first beam splitter and one of the first additional sensor corresponding to the se ¬ lected first beam splitter is different from distance between the selected first beam splitter and another of the first ad ¬ ditional sensor corresponding to the selected first beam splitter. Thus two pre-selected depths in the sample may be inspected with focus.

In another embodiment of the arrangement related to the pre ¬ ceding embodiment, difference between the distances corre- sponds to one of a depth of field value of the arrangement, a product of multiplication of a depth of field value of the arrangement with a magnification factor of the arrangement, and a product of multiplication of a depth of field value of the arrangement with a square of a magnification value of the arrangement. This provides possible ways of organizing the sensors in the first sub-assembly to image or inspect with focus different preselected parts of the sample. In certain embodiments, the difference between the sensor distances is such that the lateral planes that are imaged with focus form a continuous sequence taking into consideration the depth of field of the arrangement at the lateral planes in the sample. In another embodiment of the arrangement, at least one of the first beam splitters and the two first additional sensors corresponding to the first beam splitter is movable such that the difference between the distances is changeable. Thus one or more parts of the sample may be voluntarily brought in fo ¬ cus for a given sensor of the first sub-assembly.

In another embodiment of the arrangement, the sensor assembly includes a second sub-assembly. The second sub-assembly in- eludes one or more second beam splitters and a corresponding number of second additional sensors. The one or more second beam splitters are configured to sequentially split the se ¬ cond part of the interference pattern forming beam. Each of the one or more second beam splitters is located at a differ- ent position with respect to the primary beam splitter. Each of the one or more second beam splitters is configured to di ¬ rect different sections of the second part of the interfer ¬ ence pattern forming beam to two corresponding second additional sensor. This provides to further obtain multiple inde- pendent interference patterns at the different sensors of the second sub-assembly wherein each such interference pattern provides a focused image for a different depth in the sample or to say different lateral plane in the sample. The differ ¬ ent lateral planes are perpendicular to a direction of the probing light beam incident on the sample.

In another embodiment of the arrangement, the second addi ¬ tional sensors in the second sub-assembly are organized in a staggered arrangement. This provides a suitable arrangement to direct the parts of the interference pattern forming beam towards the different sensors by simple setup of beam split ¬ ters .

In another embodiment of the arrangement, in the second sub- assembly distance between a selected second beam splitter and one of the second additional sensor corresponding to the se ¬ lected second beam splitter is different from distance be ¬ tween the selected second beam splitter and another of the second additional sensor corresponding to the selected second beam splitter. Thus two pre-selected depths in the sample may be inspected with focus. In another embodiment of the arrangement related to the pre ¬ ceding embodiment, difference between the distances corre ¬ sponds to one of a depth of field value of the arrangement, a product of multiplication of a depth of field value of the arrangement with a magnification factor of the arrangement, and a product of multiplication of a depth of field value of the arrangement with a square of a magnification value of the arrangement. This provides possible ways of organizing the sensors in the second sub-assembly to image or inspect with focus different preselected parts of the sample. In certain embodiments, the difference between the sensor distances is such that the lateral planes that are imaged with focus form a continuous sequence taking into consideration the depth of field of the arrangement at the lateral planes in the sample. In another embodiment of the arrangement, at least one of the second beam splitters and the two second additional sensor corresponding to the second beam splitter is movable such that the difference between the distances is changeable. Thus one or more parts of the sample may be voluntarily brought in focus for a given sensor of the second sub-assembly.

In another embodiment of the arrangement, the unit includes an incident light beam splitter, a microscope objective unit and an optical setup. The incident light beam splitter re- ceives the probing light beam before the probing light beam is incident on the sample, generates the object beam and the reference beam by splitting the probing light beam, directs the object beam towards the sample and directs the reference beam away from the sample such that the reference beam is not incident on the sample. The microscope objective unit re ¬ ceives the object beam after the object beam has interacted with the sample. The optical setup receives the object beam from the microscope objective unit and the reference beam from the incident light beam splitter, combines the object beam so received and the reference beam so received to form the interference pattern forming beam, directs the interference pattern forming beam towards the sensor assembly. In an- other embodiment of the arrangement, the optical setup in ¬ cludes at least a reflector and a beam combiner. Thus the present technique is used for different path interferometry .

In another embodiment of the arrangement, alternative to pre- ceding embodiment, the arrangement includes a microscope ob ¬ jective unit. The microscope objective unit receives the probing light beam after the probing light beam has interacted with the sample. In this embodiment, the unit defines an object beam path to direct the object beam towards the sensor assembly. The unit also defines a reference beam path to di ¬ rect the reference beam towards the sensor assembly. The ob ¬ ject beam path substantially overlaps with the reference beam path. Furthermore, in this embodiment, the unit includes an interferometric unit beam splitter/combiner, an object beam reflector, a reference beam reflector, a spatial filter and a reference beam Fourier optics assembly. The interferometric unit beam splitter/combiner, hereinafter the BSC, receives the probing light beam from the microscope objective unit and splits the probing light beam so received into the object beam and the reference beam.

The object beam reflector is positioned in the object beam path and receives the object beam from the BSC and then re ¬ flects the object beam back towards the BSC. The BSC then di- rects the object beam reflected back from the object beam re ¬ flector towards the sensor assembly. The reference beam re ¬ flector is positioned in the reference beam path and receives the reference beam from the BSC and then reflects the refer ¬ ence beam back towards the BSC. The BSC then directs the ref- erence beam reflected back from the reference beam reflector towards the sensor assembly. The spatial filter is positioned optically in front of the reference beam reflector and at least partially filters out object information from the reference beam before the refer ¬ ence beam is reflected back from the reference beam reflec- tor. The reference beam Fourier optics assembly includes at least a first lens arranged at 4f configuration to a second lens. Thus the present technique is used for common path in ¬ terferometry . In another embodiment of the arrangement, the spatial filter is a pinhole. This provides a simple way of spatial filtering making the arrangement simple, compact and cost-effective.

Another aspect of the present technique presents an

interferometric microscopy method, hereinafter the method, for inspecting a sample simultaneously along different depths of the sample by inspecting the sample by an interferometric microscopy device. The sample to be inspected is probed by a probing light beam incident on the sample. In the method a sensor assembly is provided. The sensor assembly is same as disclosed hereinabove in reference to the preceding aspect of the present technique. In the method an object beam and a reference beam are generated by an interferometric unit.

Then, the object beam and the reference beam are directed to form an interference pattern forming beam directed towards the sensor assembly. Then in the method, the interference pattern forming beam is received by the primary beam splitter of the sensor assembly. Subsequently, the interference pat ¬ tern forming beam is split by the primary beam splitter into at least a first part and a second part. The first part is directed towards the first sensor and the second part is di ¬ rected towards the second sensor. Finally in the method, a first interference pattern is determined at the first sensor and a second interference pattern is determined at the second sensor. Thus different parts of the sample at different depths, when viewed along the path of probing light beam, are determined or inspected by forming focused imaged of these different parts. In an embodiment of the method, after determining the first and the second interference patterns, the first interference pattern and the second interference pattern are combined with each other to form a combined interference pattern.

In another embodiment of the method, the sensors in the sen ¬ sor assembly are organized in a staggered arrangement.

In another embodiment of the method, the first sensor is po- sitioned at a first distance from the primary beam splitter and the second sensor is positioned at a second distance from the primary beam splitter. The first distance is different from the second distance. In another embodiment of the method, difference between the first distance and the second distance corresponds to one of a depth of field value of the interferometric microscopy de ¬ vice, a product of multiplication of a depth of field value of the interferometric microscopy device with a magnification factor of the interferometric microscopy device, and a prod ¬ uct of multiplication of a depth of field value of the interferometric microscopy device with a square of a magnifi ¬ cation value of the interferometric microscopy device. Thus predetermined planes at different depths in the sample may be inspected with focus. Furthermore, it is possible, by taking a depth of field of the interferometric microscopy device in ¬ to account, to stack the focused images to represent a con ¬ tinuous section of the sample sharply or in a focused manner. The present technique is further described hereinafter with reference to illustrated embodiments shown in the accompany ¬ ing drawing, in which:

FIG 1 schematically illustrates an exemplary embodiment of an interferometric microscopy arrangement with a sensor assembly of the present technique; FIG 2 schematically illustrates an exemplary embodiment of the sensor assembly;

FIG 3 schematically illustrates an exemplary embodiment of the interferometric microscopy arrangement for different path interferometry;

FIG 4 schematically illustrates an exemplary embodiment of the interferometric microscopy arrangement for common path interferometry;

FIG 5 schematically illustrates a detailed scheme of a presently known interferometric microscopy setup for common path interferometry;

FIG 6 schematically illustrates a detailed scheme of an exemplary embodiment of the interferometric micros ¬ copy arrangement of the present technique for com ¬ mon path interferometry, as compared to the pres- ently known interferometric microscopy setup of FIG

5;

FIG 7 schematically illustrates focusing action of the interferometric microscopy arrangement of the pre ¬ sent technique;

FIG 8 schematically illustrates the sensor assembly of the interferometric microscopy arrangement of FIG 6 ; and

FIG 9 depicts a flow chart illustrating an exemplary embodiment of an interferometric microscopy method of the present technique; in accordance with aspects of the present technique.

Hereinafter, above-mentioned and other features of the pre ¬ sent technique are described in details. Various embodiments are described with reference to the drawing, wherein like reference numerals are used to refer to like elements

throughout. In the following description, for purpose of ex ¬ planation, numerous specific details are set forth in order to provide a thorough understanding of one or more embodi- ments. It may be noted that the illustrated embodiments are intended to explain, and not to limit the invention. It may be evident that such embodiments may be practiced without these specific details. It may be noted that in the present disclosure, the terms

"first", "second", "third", etc. are used herein only to fa ¬ cilitate discussion, and carry no particular temporal or chronological significance unless otherwise indicated. The basic idea of the present technique is to have two or more sensors positioned at different positions in such a way that a reference beam and an object beam emerging as a result of interferometry are combined at different sensors in a way that a part of the light beam interacting with a part of the sample is focused on one of the sensors and another part of the light beam interacting with another part of the sample is focused on the other sensor. Although both the sensors will receive light from all parts of the sample but owing to dif ¬ ferent relative positions of the sensors a first section of the image will be in focus on one sensor, say a first sensor, whereas a second section of the image will be in focus on an ¬ other sensor, say a second sensor. Thus the part of the sam ¬ ple represented in the first section will be imaged sharply by the first sensor and another part of the sample represent- ed in the second section of the image will be imaged sharply by the second sensor. Thus the different parts of the sample, that may be present at different depths in the sample, are simultaneously inspected or imaged and a desired focus is maintained in imaging these different parts of the sample.

FIG 1 schematically depicts an interferometric microscopy ar ¬ rangement 1, hereinafter the arrangement 1, according to as ¬ pects of the present technique. The sample 2 to be inspected is probed by a probing light beam 10 shined upon or shone up ¬ on the sample 2. The sample 2 has three dimensional structure extending in the Z direction for example the sample 2 is in a flow cell 3. With the arrangement 1, the sample 2 is inspect- ed simultaneously along different depths of the sample 2.

Different depths of the sample 2 may be understood as differ ¬ ent positions of different parts of the sample 2 along a di ¬ rection perpendicular to a direction in which the probing light beam 10 is incident on the sample 2. The different parts of the sample 2 may be understood as rectangular paral ¬ lelepiped shaped or cylindrical shaped sections of the sample 2, which when imaged, extends in an image or in an interference pattern, along a lateral plane i.e. along XY axis sub ¬ stantially perpendicular to the direction in which the prob- ing light beam 10 is incident on the sample 2 and having a thickness, i.e. extending along a Z axis parallel to the di ¬ rection in which the probing light beam 10 is incident on the sample 2, equal to the depth of field of the arrangement 1. The arrangement 1 includes an interferometric unit 30 and a sensor assembly 40. The interferometric unit 30, hereinafter the unit 30, generates an object beam 32 and a reference beam 34 from the probing light beam 10, either after or before the probing light beam 10 interacts with the sample 2. The object beam 32 contains or includes object information i.e. infor ¬ mation representing a characteristic of the sample 2, for ex ¬ ample a structure of a cell in the sample 2, or a morphology of a cell in the sample 2, and so on and so forth. The refer ¬ ence beam 34 either does not contain object information or object information is erased or filtered out from the refer ¬ ence beam 34 before reference beam 34 exits the unit 30. The unit 30 directs the object beam 32 having the object infor ¬ mation and the reference beam 34 devoid of the object infor ¬ mation towards the sensor assembly 40. When the reference beam 34 and the object beam 32 are directed towards the sen ¬ sor assembly 40, the reference beam 34 and the object beam 32 come together or are combined together to form an interference pattern forming beam 35 directed towards the sensor as- sembly 40. The interference pattern forming beam 35 has as its components the object beam 32 and the reference beam 34. The interference pattern forming beam 35, i.e. the object beam 32 and the reference beam 34, enters the sensor assembly

40.

The sensor assembly 40 includes a primary beam splitter 50 and a plurality of sensors 70, 80. The plurality of sensors 70, 80 includes at least a first sensor 70 and a second sen- sor 80. The primary beam splitter 50 is an optical device that receives and splits the interference pattern forming beam 35, hereinafter also referred to as the beam 35, in to at least two parts, a first part 37 and second part 38. The primary beam splitter 50 as a result of the splitting of the beam 35 creates the first part 37 of the beam 35 directed to ¬ ward the first sensor 70 and the second part 38 of the beam 35 towards the second sensor 80.

The sensors 70, 80 are optical detectors or photo-detectors. In the sensor assembly 40, hereinafter also referred to as the assembly 40, the first sensor 70 and the second sensor 80 are located at different positions with respect to the prima ¬ ry beam splitter 60, as shown in FIG 1. In the arrangement 1, the sensors 70, 80 in the sensor assembly 40 are organized in a staggered arrangement i.e. the first sensor 70, the second sensor 80 and other more sensors (not shown) are arranged in such a way that no two sensors are in a common path of light beam or in other words no two sensors of the assembly 40 are in a straight line with respect to the primary beam splitter

50.

In an exemplary embodiment of the arrangement 1, the sensors 70, 80 are positioned at different distances from the primary beam splitter 50, for example the first sensor 70 is arranged at a first distance 51 from the primary beam splitter 50 and the second sensor 80 is arranged at a second distance 52 from the primary beam splitter 50. The distances are measured along a path of propagation of a light from a given point on the primary beam splitter 50 where the light is incident on the primary beam splitter 50 to corresponding points on the first sensor 70 and the second sensor 80 where the light split by the primary beam splitter 50 meets the first sensor 70 and the second sensors 80. The first distance 51 is dif ¬ ferent from the second distance 52.

As a result of the difference in positions, more particularly as a result of the difference in the distances 51, 52 from the primary beam splitter 50, different sections of the prob ¬ ing light beam 10 will focus differently on the different sensors 70, 80, for example, say a section along a plane 7 will be focused on the first sensor 70 and a section along a plane 8 will be focused on the second sensor 80. Say if a depth of field of the arrangement 1 is ' , then a part of the sample 2 at the plane 7 will be focused sharply in the interference pattern at the first sensor 70 and also parts of the sample 2 extending in the Z axis with the plane 7 at its center and that are represented within the distance ' in the interference pattern at the first sensor 70 will also have an acceptable focus. Similarly, another part of the sam ¬ ple 2 at the plane 8 will be focused sharply in the interfer ¬ ence pattern at the second sensor 80 and also parts of the sample 2 extending in the Z axis with the plane 8 at its cen- ter and that are represented within the distance ' in the interference pattern at the second sensor 80 will also have an acceptable focus. Thus by arranging at least two sensors 70, 80 and splitting the beam 35 and directing the first part 37 and the second part 38 to different sensors 70, 80, re- spectively, the sample 2 is simultaneously inspected along different depths of the sample 2 namely at a first depth rep ¬ resented by position of the plane 7 and a second depth repre ¬ sented by position of the plane 8, the positions being deter ¬ mined along the Z direction of the sample 2.

In an exemplary embodiment of the arrangement 1, the first sensor 70 and/or the second sensor 80 and/or the primary beam splitter 50 is movable. Thus the first distance 51 and/or the second distance 52 is changeable or adjustable by an opera ¬ tor. The movements may be carried out manually or by a motor ¬ ized system (not shown) to shift the first sensor 70 and/or the second sensor 80 and/or the primary beam splitter 50 along the axis in which the distances 51 and 52 are measured. Thus, the position of the planes 7 and 8 on which interference patterns at the first and the second sensors 70, 80 re ¬ spectively are focused cab be changed to an operators liking. In another exemplary embodiment of the arrangement 1, the primary beam splitter 50, first sensor 70 and the second sensor 80 are arranged such that difference between the first distance 51 and the second distance 52 equals or substantial ¬ ly equates with a depth of field value of the arrangement 1. For arrangement 1 wherein the magnification is very low, this positioning of the sensors 70, 80 ensures that if and when the different interference patterns formed at the sensors 70, 80 are superimposed or combined with one another, two consec ¬ utive sections, for example sections along planes 7 and 8, of the sample 2 are in focus because of overlapping or contigu ¬ ous depth of fields in a final outcome obtained by stacking or superimposing or combining the different interference pat ¬ terns obtained at the sensors 70, 80. In another exemplary embodiment of the arrangement 1, the primary beam splitter 50, first sensor 70 and the second sensor 80 are arranged such that difference between the first distance 51 and the second distance 52 equals or substantial ¬ ly equates with a product of multiplication of a depth of field value of the arrangement 1 with a magnification factor of the arrangement 1. For arrangement 1, this positioning of the sensors 70, 80 ensures that if and when the different in ¬ terference patterns formed at the sensors 70, 80 are superim ¬ posed or combined with one another, two consecutive sections, for example sections along planes 7 and 8, of the sample 2 are in focus because of at least partially overlapping depth of fields in a final outcome obtained by stacking or superim- posing or combining the different interference patterns ob ¬ tained at the sensors 70, 80.

In another exemplary embodiment of the arrangement 1, the primary beam splitter 50, first sensor 70 and the second sensor 80 are arranged such that difference between the first distance 51 and the second distance 52 equals or substantial ¬ ly equates with and a product of multiplication of a depth of field value of the arrangement 1 with a square of a magnifi- cation value of the arrangement 1. For arrangement 1, this positioning of the sensors 70, 80 ensures that if and when the different interference patterns formed at the sensors 70, 80 are superimposed or combined with one another, two consec ¬ utive sections, for example sections along planes 7 and 8, of the sample 2 are in focus because of at least contiguous depth of fields in a final outcome obtained by stacking or superimposing or combining the different interference pat ¬ terns obtained at the sensors 70, 80. This relationship of positioning of the sensors 70, 80 may be extended to more sensors and with minimum number of sensors the entire depth of the sample 2 can be imaged with focus.

FIG 2 schematically represents another exemplary embodiment of the sensor assembly 40. In this embodiment of the arrange- ment 1, the sensor assembly 40 includes a first sub-assembly 41. The first sub-assembly 41 includes one or more first beam splitters 71, 73 and a corresponding number of first addi ¬ tional sensors 72, 74. The first sub-assembly 41, with the one or more first beam splitters 71, 73, sequentially splits the first part 37 of the beam 35. For example as seen in FIG 2, the first part 37 of the beam 35, before reaching the first sensor 70, is split into two by the first beam splitter 71. While one of the split parts continues towards the first sensor 70, the other split part is, as a result of the split- ting by the first beam splitter 71, directed towards the first additional sensor 72. However, as depicted in FIG 2, the other split part is split again, before reaching the first additional sensor 72, into two by the first beam split- ter 73. While one of the split parts continues towards the first additional sensor 72, the other split part is, as a re ¬ sult of the splitting by the first beam splitter 73, directed towards the first additional sensor 74. Thus the first part 37 is split by the first beam splitter 71 and split again by the first beam splitter 73, forming a sequence of splitting of the first part 37 of the beam 35. Though in FIG 2, only two splits of the first part 37 are shown - one at the first beam splitter 71 and other at the first beam splitter 73, it may be noted that the first sub-assembly 41 may includes more first beam splitters 71 which may further split parts of the first part 37 of the beam 35 continuing the sequential split ¬ ting pattern depicted by the first beam splitters 71 and 73. Thus, in the first sub-assembly 41, each of the one or more first beam splitters 71, 73 is located at a different posi ¬ tion with respect to the primary beam splitter 50, as depicted in FIG 2, and each of the one or more first beam splitters 71, 73 creates and direct a section of the first part 37 of the beam 35 towards the two corresponding first additional sensor 72 , 74.

The first additional sensors 72, 74 in the first sub-assembly 41 are organized in a staggered arrangement. Furthermore, as is depicted in FIG 2, each first beam splitter for example say first beam splitter 73 in the first sub-assembly 41 has two corresponding sensors - the first additional sensors 72 and 74. In one embodiment of the arrangement 1, each of the two corresponding sensors - the first additional sensors 72 and 74 are positioned at a different distance from their cor- responding first beam splitter 73. In an embodiment of the arrangement 1, the difference between the distances may be equal to or substantially equal to a depth of field value of the arrangement 1. In another embodiment of the arrangement 1, the difference between the distances may be equal to or substantially equal to a product of multiplication of a depth of field value of the arrangement 1 with a magnification fac ¬ tor of the arrangement 1. In yet another embodiment of the arrangement 1, the difference between the distances may be equal to or substantially equal to a product of multiplica ¬ tion of a depth of field value of the arrangement 1 with a square of a magnification value of the arrangement 1. Fur ¬ thermore, in another exemplary embodiment of the first sub- assembly 41 in the arrangement 1, the first beam splitter say 73 and/or one of the two first additional sensors 72, 74 cor ¬ responding to the first beam splitter 73 is movable such that the difference between the distances is changeable. Furthermore, as depicted in FIG 2, in an exemplary embodiment of the arrangement 1, the sensor assembly 40 includes a se ¬ cond sub-assembly 42. The second sub-assembly 42 includes one or more second beam splitters 81, 83, 85 and a corresponding number of second additional sensors 82, 84, 86. The second sub-assembly 42, with the one or more second beam splitters

81, 83, 85 sequentially splits the second part 38 of the beam 35. The sequential splitting by the second sub-assembly 42 may be understood in same manner as the sequential splitting by the first sub-assembly 41 explained hereinabove. For exam- pie as seen in FIG 2, the sequential splitting of the second part 38 is performed first by the second beam splitter 81, then by the second beam splitter 83 and then by the second beam splitter 85, and splits or parts or sections of the se ¬ cond part 38 of the beam 35 are directed to the sensors 80 and 82, the sensors 82 and 84, and the sensors 84 and 86, re ¬ spectively. Thus, in the second sub-assembly 42, each of the one or more second beam splitters 81, 83, 85 is located at a different position with respect to the primary beam splitter 50, as depicted in FIG 2, and each of the one or more second beam splitters 81, 83, 85 creates and direct a section of the second part 38 of the beam 35 towards two corresponding se ¬ cond additional sensor 82, 84, 86.

The second additional sensors 82, 84, 86 in the second sub- assembly 42 are organized in a staggered arrangement. Fur ¬ thermore, as is depicted in FIG 2, each second beam splitter for example say second beam splitter 83 in the second sub ¬ assembly 42 has two corresponding sensors - the second addi- tional sensors 82 and 84. In one embodiment of the arrange ¬ ment 1, each of the two corresponding sensors - the second additional sensors 82 and 84 are positioned at a different distance from their corresponding second beam splitter 83. In an embodiment of the arrangement 1, the difference between the distances may be equal to or substantially equal to a depth of field value of the arrangement 1. In another embodi ¬ ment of the arrangement 1, the difference between the dis ¬ tances may be equal to or substantially equal to a product of multiplication of a depth of field value of the arrangement 1 with a magnification factor of the arrangement 1. In yet another embodiment of the arrangement 1, the difference between the distances may be equal to or substantially equal to a product of multiplication of a depth of field value of the arrangement 1 with a square of a magnification value of the arrangement 1. Furthermore, in another exemplary embodiment of the second sub-assembly 42 in the arrangement 1, the se ¬ cond beam splitter say 83 and/or one of the two second addi ¬ tional sensors 82, 84 corresponding to the second beam split- ter 83 is movable such that the difference between the dis ¬ tances is changeable.

FIG 3 schematically illustrates an exemplary embodiment of the arrangement 1 for different path interferometry applica- tion. In the arrangement 1, the unit 30 includes an incident light beam splitter 11, hereinafter referred to the beam splitter 11, a microscope objective unit 20, hereinafter re ¬ ferred to as the MO unit 20, and an optical setup 90. In this embodiment of the arrangement 1, the beam splitter 11 re- ceives the probing light beam 10 before the probing light beam 10, hereinafter also referred to as the beam 10, inter ¬ acts with the sample 2. The beam splitter 11 splits the beam 10 and generates the object beam 32 and the reference beam 34. The beam splitter 11 directs the object beam 32 towards the sample 2. The object beam 32 interacts with the sample 2, collects object information from the sample 2, more particu ¬ larly from different depths of the sample 2 and continues in ¬ to the MO unit 20. The MO unit 20 includes a microscope ob- jective lens 22, hereinafter the MO 22, and a tube lens 24. The beam splitter 11 also directs the reference beam 34 away from the sample 2 such that the reference beam 34 is not in ¬ cident on the sample 2 and thus does not interact with the sample 2 and has no object information.

The optical setup 90 receives the object beam 32 from the MO unit 20. The optical setup 90 also receives the reference beam 34 from the beam splitter 11, either directly or through intermediate optical elements, for example a reflecting sur ¬ face 91, which direct the reference beam 34 to the optical setup 90. The optical setup 90 combines the object beam 32 and the reference beam 34 to form the beam 35. The beam 35 is directed by the optical setup 90 towards the sensor assembly 40. The optical setup 90 may include a reflector 92 and a beam combiner 93. The sensor assembly 40 then aids in inspecting the sample 2 simultaneously at different depths of the sample 2, for example along the planes 7 and 8, as ex ¬ plained in reference to FIG 1.

FIG 4 schematically illustrates an exemplary embodiment of the arrangement 1 for common path interferometry . In the arrangement 1, the beam 10 is shone or impinged on the sample 2 and then the beam 10 emerges after interacting with the sam- pie 2 and continues into a MO unit 20 which includes a MO 22 and a tube lens 24. The unit 30 then receives the beam 10 and define an object beam path to direct the object beam 32 to ¬ wards the sensor assembly 40 and a reference beam path to di ¬ rect the reference beam 34 towards the sensor assembly 40. The object beam path substantially overlaps with the refer ¬ ence beam path. The object beam 32 and the reference beam 34 are generated by the unit 30 by splitting the beam 10. Final ¬ ly from the unit 30 the object beam 32 and the reference beam 34 emerge to form the beam 35. Further details of the ar- rangement 1 for common path interferometry and of the unit 30 have been explained hereinafter with reference to FIGs 5 to 8. Referring to FIGs 5 and 6 comparatively, the arrangement 1 of the present technique has been explained further. FIG 5 de ¬ picts a setup of common path interferometry; the beam 10 incident on the sample 2 is collected by the MO 20 and focused by the tube lens 24 to form an intermediate image 98. Actions of the MO 20, tube lens 24 and formation of intermediate im ¬ age 98 are well known in field of microscopy so not explained herein in details for sake of brevity. The beam 10 continues into the unit 30 wherein the beam 10 passes through a first lens 64 arranged in 4f configuration to a second lens 24, i.e. the tube lens 24. The beam 10 then is split by an interferometric unit beam splitter/combiner 33, hereinafter BSC 33. The unit 30 also has an optical beam reflector 102, hereinafter the reflector 102, and a reference beam reflector 104, hereinafter the reflector 104. The BSC 33 along with the reflector 102 defines a path for the object beam 32 known as the optical beam path. Similarly, the BSC 33 along with the reflector 104 defines a path for the reference beam 34 known as the reference beam path. The BSC 33 receives the beam 10 and splits the beam 10 into an object beam 32 directed along the optical beam path and a reference beam 34 directed along the reference beam path.

The optical beam 32 directed by the BSC 33 towards the re- flector 102 is reflected back to the BSC 33 by the reflector 102. The reference beam 34 is directed by the BSC 33 towards the reflector 104. However, before the reference beam 34 reaches the reflector 104, the reference beam 34 encounters a spatial filter 66, for example a pinhole, positioned in front of the reflector 104. The reference beam 34 is filtered by the spatial filter 66 and object information is deleted or erased or removed from the reference beam 34 before the ref ¬ erence beam 34 is reflected by the reflector 104 back to the BSC 33. The object beam 32 and the spatially filtered refer- ence beam 34 combine at the BSC 33.

In known interferometric techniques, the reference beam 34 and the object beam 32 are directed towards an optical sens- ing element 95 on which an image or interference pattern is formed by superimposition of the object beam 32 and the ref ¬ erence beam 34. However, the image formed at the detector 95 has focus which represents sample 2 along a plane 6. A posi- tion of the plane 6 is represented by a dot marked with ref ¬ erence numeral 99 in FIGs 5, 6 and 7. A position of the fo ¬ cus, after the unit 30, for the plane 6 is represented by a dot marked with reference numeral 99' in FIGs 5, 6 and 8. As can be seen from FIG 5, the plane 6 at position 99 is focused on the detector 95 which is at the position 99' . However, as also seen in FIG 5, parts of the sample 2 along other planes above and below the plane 5, for example planes 4, 5, 7 and 8 are not focused on the detector 95. As shown in FIG 6 in combination with FIGs 7 and 8, it can be seen that by positioning different sensors 70, 72, 80, 82 at different positions with respect to the primary beam splitter 50 and by directing segments of the beam 35 to each of these sensors 70, 72, 80, 82 different planes 4, 5, 7 and 8 of the sample 2 are focused on different sensors 70, 72, 80, 82. For example, as shown in FIG 6, and more clearly in FIGs 7 and 8, a position of the sensor 70 is removed by a distance ' i.e. distance d away from the position 99' in direction opposite to the primary beam splitter 50 and as a result light from a different part of the sample 2, i.e. from a different depth of the sample 2, for example from the plane 5 will now be fo ¬ cused on the sensor 70. Similarly, a position of the sensor 80 is removed by a distance x -d' i.e. distance d away from the position 99' and towards the primary beam splitter 50 and as a result light from a different part of the sample 2, i.e. from a different depth of the sample 2, for example from the plane 7 will now be focused on the sensor 70. Similarly, the sensors 72 and 82 are removed by a distance x 3d' and x -3d' from the position 99' , respectively and form the focused im- ages for example of planes 4 and 8, respectively. Further ¬ more, if the magnification factor of the arrangement 1 is known and the depth of field is known, the sensors 70, 72, 80, 82 may be arranged such that sample 2 from all possible depths of the sample 2 is imaged within a depth of field and thus high focus image or high contrast image of the entire depth of the sample 2 is obtained. Now referring to FIG 9, a flow chart of an interferometric microscopy method 1000, hereinafter the method 1000, repre ¬ senting an exemplary embodiment of the method 1000 of the present technique has been explained hereinafter in combina ¬ tion with to FIGs 1 to 8. The sample 2 to be inspected is probed by a probing light beam 10 shined upon the sample 2. In the method 1000, a sensor assembly 40 is provided in step 300. The sensor assembly 40 is same as disclosed hereinabove in reference to the preceding aspect of the present tech ¬ nique, particularly described in reference to FIGs 1 to 8. In the method 1000 an object beam 32 and a reference beam 34 are generated in a step 200 by an interferometric unit 30. The interferometric unit 30 and the generation of the object beam 32 and the reference beam 34 may be understood as described hereinabove in reference to the preceding aspect of the pre- sent technique, particularly described in reference to FIGs 1 to 8. Then, the object beam 32 and the reference beam 34 are directed in a step 400 to form an interference pattern form ¬ ing beam 35 directed towards the sensor assembly 40. Then in the method 1000, the beam 35 is received by the primary beam splitter 50 of the sensor assembly 40 in a step 500. Subse ¬ quently, in a step 600 the beam 35 is split by the primary beam splitter 50 into at least a first part 37 and a second part 38. Thereafter in the method 1000, in a step 700, the first part 37 is directed towards the first sensor 70 and the second part 38 is directed towards the second sensor 80. Fi ¬ nally in the method 1000, in a step 800, a first interference pattern is determined at the first sensor 70 and a second in ¬ terference pattern is determined at the second sensor 80. Thus different parts of the sample 2 at different depths, when viewed along the path of probing light beam 10, are de ¬ termined or inspected by forming focused imaged of these dif ¬ ferent parts. Additionally in an embodiment of the method 1000, after the step 800, in a step 900 the first interference pattern and the second interference pattern are combined with each other to form a combined interference pattern.

While the present technique has been described in detail with reference to certain embodiments, it should be appreciated that the present technique is not limited to those precise embodiments. Rather, in view of the present disclosure which describes exemplary modes for practicing the invention, many modifications and variations would present themselves, to those skilled in the art without departing from the scope and spirit of this invention. The scope of the invention is, therefore, indicated by the following claims rather than by the foregoing description. All changes, modifications, and variations coming within the meaning and range of equivalency of the claims are to be considered within their scope.