WO2017041843A1

WO2017041843A1 - A technique for illuminating a sample to be inspected by interferometric microscopy

Info

Publication number: WO2017041843A1
Application number: PCT/EP2015/070630
Authority: WO
Inventors: Anton Schick; Oliver Hayden; Oliver Schmidt
Original assignee: Siemens Healthcare Gmbh
Priority date: 2015-09-09
Filing date: 2015-09-09
Publication date: 2017-03-16

Abstract

A condenser lens, and an interferometric microscopy arrangement based on the condenser lens and a method based on the condenser lens are presented. The condenser lens shines a light beam from an illumination source onto a sample that is to be inspected by an interferometric microscopy device. The light beam from the illumination source has a first wavefront. The condenser lens includes a non-condensing region and a condensing region. The non-condensing region receives a first part of the light beam from the illumination source and transmits the first part towards the sample. The first part of the light beam so transmitted has the first wavefront. The condensing region receives a second part of the light beam from the illumination source and transmits the second part towards the sample. The second part of the light beam so transmitted has a second wavefront. The first wavefront is different from the second wavefront.

Description

A technique for illuminating a sample to be inspected by interferometric microscopy

The present invention relates to interferometric techniques, and more particularly to a condenser lens for interferometric microscopy devices, an interferometric microscopy arrangement using the condenser lens and a method of interferometric in- spection using the condenser lens.

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) . An emerging technique in interferometric microscopy is common path interferometry in which 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.

The common path interferometry differs from the commonly known different path interferometry in the sense that unlike the different path interferometry where the light beam is split into the reference beam and the object beam before in^¬ teracting with the sample, in common path interferometry the light beam is split into the reference beam and the object beam after interaction with the sample. In different path interferometry, only the object beam interacts with the sample, whereas in the common path interferometry, an incoming beam interacts with the sample and emerges from the sample con- taining the object information and then this emergent beam is divided into the reference beam and the object beam, and sub^¬ sequently the object information from the reference beam is deleted or filtered before the reference beam and the object beam are superimposed to form the interference pattern as an output of the interferometry from which the amplitude and phase information are analyzed that represent characteristics of the sample such as physical structures in the sample, den^¬ sity of the sample, and so on and so forth. A major advantage of common path interferometry over the different path inter- ferometry is stability because unlike different path inter- ferometry in common path interferometry the light beam interacting with the sample travels as one and is split and sub^¬ jected to different paths - namely an object beam path and a reference beam path only for short travel distances as com^¬ pared to different path interferometry where the light beam is split much earlier and thus chances of introduction of error are high. In known common path interferometric techniques, a single in^¬ coming beam of collimated coherent light is interacted with the sample and then split into the reference beam and the ob^¬ ject beam by a beam splitter. The object beam is then subjected to spatial filtering to erase or filter out object in- formation from the reference beam and then the reference beam is superimposed with the object beam. Using a collimated beam is necessary for the above described common path

interferometric technique to maintain a desired intensity in the reference beam after spatial filtering, and thus use of any condenser or focusing action of the light beam right before interacting with the sample is highly undesirable as it will lead to having a very low intensity reference beam and thus the interference pattern produced as an output will be unsuitable or of poor quality.

Thus, lateral resolution of such a device or setup of pres^¬ ently known common path interferometric techniques is low be^¬ cause of the necessity to use a collimated beam of light to impinge on the sample, as explained above. As is commonly known, equation 1 below presents a measure of lateral resolu^¬ tion for microscopy: λ

d oc

^^objective ^^Condenser wherein d is measure of distance, λ is wavelength of the in^¬ coming beam, NA_obj_ective i s numerical aperture of the objective lens of the microscope and NA_Condenser is numerical aperture of the condenser of the microscope. Smaller the value of d bet- ter is the lateral resolution of the microscopy device. In the case of common path interferometry NA_Condenser = 0 because condenser is not used since the use of condenser is detri^¬ mental to the intensity of the reference beam and thus to the final obtained interference pattern.

Thus the object of the present disclosure is to provide a technique for improving present day interferometric devices and setups, more particularly improving a lateral resolution of present day common path interferometric techniques and simultaneously maintaining a desired intensity in the refer^¬ ence beam.

The above objects are achieved by a condenser lens according to claim 1, an interferometric microscopy arrangement according to claim 7 and a method according to claim 15 of the pre^¬ sent technique. Advantageous embodiments of the present tech^¬ nique are provided in dependent claims. Features of claim 1 may be combined with features of dependent claims dependant on claim 1, and features of dependent claims can be combined together. Similarly, features of claim 7 may be combined with features of dependent claims dependant on claim 7, and fea^¬ tures of dependent claims can be combined together. Further^¬ more, features of claim 15 may be combined with features of dependent claims dependant on claim 15, and features of de^¬ pendent claims can be combined together. According to a first aspect of the present technique, a con^¬ denser lens is presented. The condenser lens shines or di^¬ rects a light beam from an illumination source onto a sample. The sample is to be inspected by an interferometric microsco- py device. The light beam from the illumination source has a first wavefront. The condenser lens includes a non-condensing region and a condensing region. The non-condensing region receives a first part of the light beam from the illumination source and transmits the first part of the light beam so re- ceived towards the sample. The part of the light beam re^¬ ceived and transmitted by the non-condensing region retains the first wavefront after transmission by the non-condensing region. The condensing region receives a second part of the light beam from the illumination source and transmits the se- cond part of the light beam so received towards the sample such that the second part of the light beam so transmitted by the condensing region has a second wavefront. The first wave- front is different from the second wavefront. Thus, a part, i.e. the first part, of the light beam passing through one part of the lens i.e. the non-condensing region passes through the lens without any substantial change in the wave- front or the form of the waves whereas another part i.e. the second part, of the light beam passing through another part of the lens i.e. the condensing region while passing through the lens undergoes substantial change in the wavefront or the form of the waves and emerges from the condensing region of the lens with a new form of wavefront i.e. the second wave- front . Thus, if the light beam is collimated light, a part, i.e. the first part, of the light beam entering a face of the conden^¬ ser lens and passing through the non-condensing region, remains collimated when emerging from an opposite face of the condenser lens; whereas another part i.e. the second part, of the collimated light beam entering the face of the condenser lens and passing through the condensing region, changes in wavefront and becomes curved or focused while passing through the lens and emerges from the condensing region of the lens with a new form of wavefront i.e. the second wavefront which may be, for example, curved as a result of change from the collimated light beam effected by the condensing region.

Thus, by use of the condensing lens of the present technique, the light beam shone upon the sample, and emerging after in^¬ teracting with the sample, has at least two components - a first component that interacted with the sample as a colli^¬ mated beam and thus is well suited for extracting a reference beam later on, and a second component that interacted with the sample as a curved or focused beam and thus contains more object information and subsequently increases a lateral reso^¬ lution of the image or image data detected as a result of in^¬ specting with the interferometric microscopy device. The re^¬ sultant increase in lateral resolution is because the part of the light beam passing through the condensing region has an effect of numerical aperture of the condensing region in its lateral resolution.

In an embodiment of the condenser lens, the non-condensing region and the condensing region are adjoining each other and formed as a single physical entity. Thus the condenser lens is formed as a single physical entity having the non- condensing region and the condensing region and is easy to integrate into existing interferometric microscopy setups.

In another embodiment of the condenser lens, the condensing region peripherally surrounds the non-condensing region. Thus the part of the light beam focused from the condensing region has a greater angle of incidence upon the sample.

In another embodiment of the condenser lens, the non- condensing region is flat disc shaped and the condensing region is annular in shape. This presents a simple design to fabricate the condenser lens.

In another embodiment of the condenser lens, the non- condensing region is located centrally. This presents another simple design to fabricate the condenser lens. Moreover since the non-condensing region is positioned centrally, an exist^¬ ing lens can be easily modified by grinding an existing lens at the center where the existing lenses are less curved and thus the manufacture of the condenser lens of the present technique is simple and easily implementable .

In another embodiment of the condenser lens, the non- condensing region comprises a hole. This provides a simplest design of the condenser lens of the present technique.

In another embodiment of the condenser lens, the non- condensing region and the condensing region comprise a same transparent material. Thus any effects attributed to the light beam solely as a result of the material of the non- condensing region and the condensing region of the condenser lens is constant for the parts of the light beam transmitted from the non-condensing region and the condensing region because the non-condensing region and the condensing region are formed of the same material.

According to a second aspect of the present technique, an interferometric microscopy arrangement for inspecting a sam^¬ ple is presented. The sample is placed in a sample port and is inspected by shining a light beam from an illumination source onto the sample and detecting an interference pattern at an optical detector. The light beam from the illumination source has a first wavefront. The interferometric microscopy arrangement includes a condenser lens and an interferometric unit. The condenser lens is optically positioned between the illumination source and the sample port. The condenser lens is same as the condenser lens presented in the first aspect of the present technique. The interferometric unit is posi^¬ tioned optically downstream of the sample port. The

interferometric unit receives the light beam transmitted by the condenser lens after interacting with the sample. The interferometric unit then generates from the light beam so received an object beam and a reference beam. The

interferometric unit directs the object beam and the refer- ence beam towards the optical detector to form the interfer^¬ ence pattern at the optical detector. The interference pat^¬ tern at the optical detector is formed by interaction, i.e. interference, of the object beam and the reference beam. The lateral resolution of the interferometric microscopy arrange^¬ ment of the present technique is enhanced due to the condens^¬ ing region of the condenser lens of the present technique compared to a setup which does not use any commonly known condenser before the light beam interacts with the sample. Moreover, at the same time along with increased lateral reso^¬ lution, the reference beam has a greater intensity due to the non-condensing region compared to a setup which uses any commonly known condenser before the light beam interacts with the sample.

In an embodiment of the interferometric microscopy arrange^¬ ment, the interferometric microscopy arrangement includes the illumination source. Thus an alignment of the illumination source and the condenser lens may be fixed. Moreover, a wave- front altering power, i.e. capability to alter the first waveform to the second waveform for example altering colli- mated to focused wavefront, and a level of such alteration, can be fixed by selecting a particular condenser lens for a given illumination source.

In another embodiment of the interferometric microscopy ar^¬ rangement, the illumination source provides at least one of collimated light, coherent light and a combination thereof. The different light forms have their own advantages. A good example may be a Laser or a super-luminescent diode (SLED) .

In another embodiment of the interferometric microscopy ar^¬ rangement, the interferometric unit defines an object beam and a reference beam path. The object beam path is for di- recting the object beam towards the optical detector. The reference beam path is for directing the reference beam to^¬ wards the optical detector. The object beam path substantial^¬ ly overlaps with the reference beam path. The interferometric unit includes a beam splitter/combiner, an object beam reflector, a reference beam reflector, a spatial filter and a reference beam Fourier optics assembly. The beam splitter/combiner receives the light beam transmit^¬ ted by the condenser lens and splits the light beam so re^¬ ceived into the object beam and the reference beam. The ob^¬ ject beam reflector is positioned in the object beam path and receives the object beam from the beam splitter/combiner. Subsequently, the object beam reflector reflects the object beam back towards the beam splitter/combiner. The beam splitter/combiner directs the object beam reflected back from the object beam reflector towards the optical detector. The ref^¬ erence beam reflector is positioned in the reference beam path and receives the reference beam from the beam split^¬ ter/combiner and reflects the reference beam back towards the beam splitter/combiner. The beam splitter/combiner directs the reference beam reflected back from the reference beam re^¬ flector towards the optical detector. The spatial filter is positioned optically in front of the reference beam reflector and at least partially filters object information from the reference beam before the reference beam is reflected back from the reference beam reflector. The reference beam Fourier optics assembly includes at least a first lens arranged at 4f configuration to a second lens. This presents an optical set^¬ up of the interferometric unit well suited for functioning along with the condenser of the present technique.

In another embodiment of the interferometric microscopy ar- rangement, the spatial filter is a pinhole. This presents a simple design of the spatial filter.

In another embodiment, the interferometric microscopy ar^¬ rangement includes an objective lens configured to receive the light beam after interaction with the sample. The first lens is positioned such that a Fourier plane of the objective lens coincides with a focal plane of the first lens. Further^¬ more, the spatial filter is positioned at a focal plane of the second lens. This presents an effective and simple setup to achieve substantial spatial filtering of the reference beam. In another embodiment, the interferometric microscopy ar^¬ rangement includes a third lens positioned at 4f configura^¬ tion with respect to the second lens. The third lens is posi^¬ tioned in front of the optical detector and facilitates for^¬ mation of the interference pattern on the optical detector.

According to a third aspect of the present technique, a meth^¬ od for inspecting a sample by shining a light beam from an illumination source onto the sample is presented. The light beam from the illumination source has a first wavefront. In the method, the light beam from the illumination source is shined onto a condenser lens. In the method, the condenser lens is same as the condenser lens presented according to the first aspect of the present technique. The light beam trans^¬ mitted by the condenser lens shines upon the sample. Thereaf- ter, the light beam transmitted by the condenser and after interaction with the sample is received by a beam split^¬ ter/combiner. Subsequently, the light beam so received is split, by the beam splitter/combiner, into an object beam and a reference beam. Thereafter, spatial filtering of the refer- ence beam by a spatial filter is performed. In the spatial filtering, object information is at least partially filtered out from the reference beam. Then, the spatially filtered reference beam and the object beam are directed towards an optical detector. Finally, an interference pattern is detect- ed at the optical detector. The interference pattern results from first part of the light beam that interacted with the non-condensing region and then with the sample, and thus provides a suitable reference beam, and the second part of the light beam that interacted with the condensing region and then with the sample, and thus has more object information than the first part of the light beam and this helps in in^¬ creased lateral resolution of detection in the method and ob^¬ taining of a desired intensity of the reference beam depend- ing upon a ratio of the condensing region and the non- condensing region in the condenser lens.

In an embodiment of the method, the light beam is one of co- herent light, collimated light, and a combination thereof. The different light forms have their own advantages in form^¬ ing interference patterns after interacting with the sample. A good example may be a Laser or a super-luminescent diode (SLED) .

In another embodiment of the method, at least one of the splitting of the light beam, the spatial filtering of the reference beam, the directing of the spatially filtered ref^¬ erence beam and the object beam towards the optical detector, and a combination thereof is performed within an

interferometric unit. The interferometric unit is same as the interferometric unit presented in the second aspect of the present technique. The present technique is further described hereinafter with reference to illustrated embodiments shown in the accompany^¬ ing drawing, in which:

FIG 1 schematically illustrates a top view of an exempla- ry embodiment of a condenser lens of the present technique ;

FIG 2 schematically illustrates a cross-sectional view of the exemplary embodiment of the condenser lens of FIG 1;

FIG 3 schematically illustrates an exemplary

interferometric microscopy setup without the con^¬ denser lens of FIG 1 ;

FIG 4 schematically illustrates an exemplary

interferometric microscopy setup with the condenser lens of FIG 1; FIG 5 schematically illustrates the exemplary interferometric microscopy setup of FIG 4 further explaining action of the condenser lens of FIG 1 ;

FIG 6 schematically illustrates a top view of another ex^¬ emplary embodiment of the condenser lens of the present technique; FIG 7 schematically illustrates a cross-sectional view of the exemplary embodiment of the condenser lens of FIG 6;

FIG 8 schematically illustrates an exemplary embodiment of an interferometric microscopy arrangement of the present technique; and

FIG 9 depicts a flow chart illustrating an exemplary embodiment of a 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. FIG 1 schematically illustrates a top view of an exemplary embodiment of a condenser lens 10 of the present technique and FIG 2 schematically illustrates a cross-sectional view of the exemplary embodiment of the condenser lens 10 of FIG 1. The condenser lens 10 is for use with or in interferometric microscopy techniques, more particularly for use with or in common path interferometric microscopy techniques. Before delving deeper into structure and function of the condenser lens 10 it may be helpful to understand an interferometric microscopy setup without the condenser lens 10.

As shown in FIG 3, an exemplary interferometric microscopy setup, more particularly an exemplary common path

interferometric microscopy setup, without the condenser lens 10 of FIG 1 is depicted. In such a setup as depicted in FIG 3, a light beam 2, or a collimated light beam 2 produced by an illumination source 20 such as a Laser is shined upon a sample 99. Arrows marked with reference numeral 8 depict a direction of the light beam 2 from the illumination source 20 towards the sample 99. The light beam 2 impinges or interacts with the sample 99 and emerges from the sample 99 and subse^¬ quently is received by an interferometric microscopy device 98 that creates a reference beam (not shown) and an object beam (not shown) and then superimposes the reference beam, after filtering out object information from the reference beam, and the object beam to create an interference pattern as an output of the interferometric microscopy setup. As can be seen the light beam 2 before impinging on to the sample 99 has a first wavefront 3, particularly a collimated wavefront 3, for reasons explained hereinabove. The condenser lens 10, or simply the condenser 10, of the present technique is for use with such common path interferometric microscopy setup.

In contrast to FIG 3, FIG 4 schematically illustrates an ex- emplary interferometric microscopy setup with the condenser lens 10 of FIG 1. Similarly, FIG 5 schematically illustrates the exemplary interferometric microscopy setup of FIG 4 fur^¬ ther explaining action of the condenser lens of FIG 1. The condenser lens 10 has been explained hereinafter with reference to FIGs 1 and 2 in combination with FIGs 3, 4 and 5.

The condenser lens 10 includes a non-condensing region 12 and a condensing region 16. The non-condensing region 12 when positioned optically in between the illumination source 20 and the sample 10 receives a first part 4, as shown in FIG 5, of the light beam 2 from the illumination source 20. The first part 4 is then transmitted through or passes through or travels through or propagates through the non-condensing region 12 and emerges out of the condenser lens 10, more particularly out of the non-condensing region 12 of the condenser lens 10, on the other side of the illumination source 20 i.e. towards the sample 99. The non-condensing region 12 is such that the first part 4 of the light beam 2 so transmitted by or through the non-condensing region 12 has the first wavefront 3 i.e. the wavefront 3 of the light beam 2 remains unchanged for the part i.e. the first part 4 that propagates through the non-condensing region 12 of the condenser lens 10

The non-condensing region 12 may be understood as a part of the condenser lens 10 with low, compared to the condensing region 16, or preferably zero numerical aperture. For example the non-condensing region 12 may be a hole 13, as shown in FIGs 6 and 7. Thus the light beam 2 passes through the hole 13 without undergoing any change in the wavefront 3. Since the hole 13, i.e. the non-condensing region 12 has no material, like glass or transparent polymer, there is only air or any ambient fluid present in the hole 13, same as the air or the ambient fluid present between the condenser lens 10 and the illumination source 20, and thus while passing through the non-condensing region 12, the light beam 2 does not undergo any change in the wavefront. The non-condensing region 12 of the condenser lens 10 is such that the light beam 2 incoming into one face of the non-condensing region 12 emerges from the opposite face of the non-condensing region 12 without any variation in the wavefront of the emerging light beam 2 compared to the incoming light beam 2. Thus the non-condensing region 12 of the condenser lens 10 is such that if the incoming light beam 2 is collimated then the light beam emerging out of the non-condensing region 12 part of the condenser lens 10 remains collimated.

The condensing region 16 when positioned optically in between the illumination source 20 and the sample 10 receives a second part 5, as shown in FIG 5, of the light beam 2 from the illumination source 20. The second part 5 is then transmitted through or passes through or travels through or propagates through the condensing region 16 and emerges out of the condenser lens 10, more particularly out of the condensing region 16 of the condenser lens 10, on the other side of the illumination source 20 i.e. towards the sample 99. The con- densing region 16 is such that the second part 5 of the light beam 2 so transmitted by or through the condensing region 16 has a second wavefront 6 i.e. the wavefront 3 of the light beam 2 changes for the part i.e. the second part 5 that propagates through the condensing region 16 of the condenser lens 10. The first wavefront 3 and the second wavefront 6 are different from each other, i.e. for example, as shown in FIG 4, the first wavefront 3 may be, but not limited to collimated wavefront or wavefront parallel to a sample plane 97 i.e. a plane on which or parallel to which the sample 99 may be ar- ranged, and the second wavefront 4 is focused wavefront or wavefront curved with respect to the sample plane 99, or to put simple plane waves 3 changed to curved waves 4.

The condensing region 16 may be understood as a part of the condenser lens 10 with high, compared to the non-condensing region 12, numerical aperture, for example the condensing region 16 may be understood as peripheral or non central parts of a focusing lens. Thus while the light beam 2 is passing through the focusing lens part of the condenser lens 10, i.e. the condensing region 16, the light beam 2 undergoes a change in the wavefront 3 and emerges out of the condensing region 16 with a new wavefront i.e. the second wavefront 4. The condensing region 16 of the condenser lens 10 is such that the light beam 2 incoming into one face of the condensing region 16 emerges from the opposite face of the condensing region 16 with a changed wavefront of the emerging light beam 2 compared to the incoming light beam 2. Thus the condensing re- gion 16 of the condenser lens 10 is such that if the incoming light beam 2 is collimated then the light beam emerging out of the condensing region 16 part of the condenser lens 10 does not remain collimated, but instead becomes focused towards the sample 99 or the sample plane 97.

Thus the light beam 2 emerging out of the condenser lens 10 before interacting with the sample 99 has essentially at least two components - one a collimated component formed out of the first part 4 of the light beam 2 and other the focused component formed out of the second part 5 of the light beam 2. The focused component is focused according to a numerical aperture of the condensing region 16 of the condenser lens 10. Later these two parts - the collimated component and the focused component interact with the sample 99 and emerge out of the sample 99. Later on in the interferometric technique, the collimated component is used primarily to generate a ref^¬ erence beam (not shown) and the focused part is used to pri^¬ marily generate an object beam (not shown) . Since, a ratio of the collimated component and the focused component of the light beam 2 can be achieved as desired by a ratio of the non-condensing region 12 and the condensing region 16, a desired intensity of the reference beam may be achieved. Fur^¬ thermore, since the numerical aperture of the condensing re^¬ gion 16 is non zero i.e.

^^Condenser ^ 0 the value of d is smaller compared to the value of d ob^¬ tained from equation 1 hereinabove if all other parameters are constant. Smaller the value of d better is the lateral resolution of the microscopy device with the condenser lens 10 of the present technique. In an exemplary embodiment of the condenser lens 10, the non- condensing region 12 and the condensing region 16 are adjoining each other and formed as a single physical entity 11. As shown in FIGs 1 to 7 , the non-condensing region 12 and the condensing region 16 are not a combination of two separate lenses, but the condenser lens is a single lens with a part of the lens formed as the non-condensing region 12 and another part of the lens formed as the condensing region 16. In an exemplary embodiment (not shown) the non-condensing region 12 and the condensing region 16 may be formed side-by side and the non-condensing region 12 is adjoining the condensing region 16 along one edge and not entire boundary of the non-condensing region 16. In an alternate embodiment, the condensing region 16 peripherally surrounds the non- condensing region 12, as shown in FIGs 1, 2, 6 and 7. The non-condensing region 12 may be, but not limited to, flat disc shaped and the condensing region 16 may be annular in shape surrounding the flat disc shaped non-condensing region 12. Preferably, the non-condensing region 12 is located centrally, as shown in FIGs 1 and 6. As described hereinabove, in one exemplary embodiment of the condenser lens 10, the non-condensing region 12 may be the hole 13. In an alternate exemplary embodiment of the condenser lens 10, the non- condensing region 12 and the condensing region 16 are formed of a same transparent material, for example, but not limited to, glass or polymer. However, a surface (now shown) of the non-condensing region 12 is preferably flat compared to a surface (now shown) of the condensing region 16 which is curved towards edges of the condenser lens 10.

The condenser lens 10 may be designed as flat surfaced rectangular parallelepiped, for example a cube, forming the non- condensing region 12 embedded in a central part of a biconvex lens such that the flat surfaced rectangular parallelepiped is aligned with a central longitudinal axis of the biconvex lens, i.e. the axis of the biconvex lens parallel to a focal plane of the biconvex lens, and such that two opposing sides of the flat surfaced rectangular parallelepiped are exposed at opposing surfaces of the biconvex lens, and wherein the peripheral surfaces of the biconvex lens form the condensing region 16 of the condenser lens 10. The condenser lens 10 may also be designed as flat surfaced cylinder forming the non- condensing region 12 embedded in a central part of a biconvex lens such that the flat surfaced cylinder is aligned with a central longitudinal axis of the biconvex lens, i.e. the axis of the biconvex lens parallel to a focal plane of the bicon- vex lens, such that the axis of the cylinder is parallel to the focal plane of the biconvex lens and such that two opposing flat sides of the cylinder are exposed at opposing surfaces of the biconvex lens, and wherein the peripheral surfaces of the biconvex lens, i.e. surface of the biconvex lens where the surfaces of the cylinder are not exposed, form the condensing region 16 of the condenser lens 10.

Referring to FIG 8, in combination with FIGs 1 to 7, another aspect of the present technique has been explained hereinaf- ter. FIG 8 schematically illustrates an exemplary embodiment of an interferometric microscopy arrangement 1, hereinafter the arrangement 1, of the present technique. The arrangement 1 includes the condenser lens as described in reference to the first aspect of the present technique, particularly in reference to FIGs 1 to 7. The arrangement 1 also includes an interferometric unit 30, hereinafter referred to as unit 30. The arrangement 1 may optionally include the illumination source 20. The arrangement 1 is used to inspect the sample 99 placed in a sample port 90 which may be, but not limited to a slide or a transparent substrate capable of holding the sample 99.

In the arrangement 1, the light beam 2 is provided by the il^¬ lumination source 20. The light beam 2 provided by the illu- mination source 20 is collimated or coherent or both, for ex^¬ ample the illumination source 20 may be, but not limited to, Laser, SLED, and so on and so forth. The light beam 2 has the first wavefront 3 when the light beam 2 leaves the illumina- tion source 20 towards the condenser lens 10. The condenser lens 10 is optically positioned between the illumination source 20 and the sample port 90 meaning thereby that the light beam 2 provided by the illumination source 20 travels or propagates to the condenser lens 10 and then to the sample 99 placed in the sample port 90. As a result of propagating through the non-condensing region 12 of the condenser lens 10, a part, i.e. the first part 4, as shown in FIG 5, travels through the non-condensing region 12 without undergoing change in the wavefront i.e. the collimated light beam 2 re^¬ mains collimated when passing through the condenser lens 10, as depicted schematically by straight lines in FIG 8 and FIG 5. However, as a result of propagating through the condensing region 16 of the condenser lens 10, another part, i.e. the second part 4, as shown in FIG 5, while travelling through the condensing region 16 undergoes change in the wavefront i.e. the collimated light beam 2 becomes focused light beam 2 as a result of passing through the condenser lens 10. The light beam 2 with the collimated part and the focused part falls on or interacts with the sample 99 in the sample port 90. Both parts of the light beam 2 pickup or collect or gather object information i.e. the information about the sample for example about physical structure of a red blood cell in the sample 99. Both the parts - the collimated part and the focused part - as part of the light beam 2 then are re^¬ ceived by an objective lens 80, which can be understood as a commonly used microscope objective. As a result of passing through the objective lens 80, the collimated part is focused on a Fourier plane 82 of the objective lens 80. Both the parts of the light beam 2 - the collimated part and the fo^¬ cused part - as part of the light beam 2 then are incident on a first lens 72 which is arranged such that a focal plane 73 of the first lens 72 coincides with the Fourier plane 82 of the objective lens 80.

The light beam 2 after passing through the first lens 72 propagates to and is incident upon a second lens 74. The first lens 72 and the second lens 74 are arranged in 4f con^¬ figuration with respect to each other. The first lens 72 and the second lens 74 form a reference beam Fourier optics as^¬ sembly 70. An other focal plane 71 of the first lens 72 coin- cides with a focal plane 75 of the second lens.

The reference beam Fourier optics assembly 70 may be a part of the unit 30. The unit 30 is positioned optically down^¬ stream of the sample port 90. The unit 30 includes a beam splitter/combiner 32, hereinafter BSC 32. The BSC 32 receives the light beam 2 transmitted through the condenser lens 10 after interacting with the sample 99. Beam splitters/combiners are well known in the art of optics and thus not explained herein in details for sake of brevity. The BSC 32 splits the light beam 2 into an object beam 52 and a ref^¬ erence beam 54. The object beam 52 travels along an object beam path and is directed towards an object beam reflector 62. The object beam reflector 62 functions to reflect the ob^¬ ject beam 52 back towards the BSC 32. The object beam reflec- tor 62 may be a simple reflector such as, but not limited to, a plane mirror, a reflecting prism, or a retroreflector . The object beam 52 includes both parts - the part coming from the collimated part of the light beam 2 and the part coming from focused part of the light beam 2. The object beam 52 after being received by the BSC 32 as a result of being reflected back by the object beam reflector 62 is directed by the BSC 32 towards an optical detector 95.

The reference beam 54 travels along a reference beam path and is directed towards a reference beam reflector 64. The refer^¬ ence beam reflector 64 functions to reflect the reference beam 54 back towards the BSC 32. The reference beam reflector 64 may be a simple reflector such as, but not limited to, a plane mirror, a reflecting prism, or a retroreflector . The reference beam 54 includes both parts - the part coming from the collimated part of the light beam 2 and the part coming from focused part of the light beam 2. The arrangement 1 further includes in the unit 30 a spatial filter 66, for example a pin hole, positioned optically in front of the reference beam reflector 64 as the reference beam 54 travels from the BSC 32 towards the reference beam reflector 64. The spatial filter 66 is arranged at an other focal plane 75 of the second lens 74. The spatial filter 66 filters out object information from the reference beam part of the light beam 2 coming from the collimated part and com^¬ pletely removes the part of the light beam 2 coming from the focused part of the light beam 2. Thus only the reference beam 54 resulting from the collimate part of the light beam 2 is reflected back to the BSC 32 by the reference beam reflec^¬ tor 64 and the reference beam 54 so reflected back to the BSC 32 is spatially filtered i.e. at least parts of the object information are filtered out. The technique of spatial fil^¬ tering, including use of pin hole as spatial filer, to delete or filter out object information from a light is well known in the art of optics and thus not explained herein in details for sake of brevity. The spatially filtered reference beam 54 after being received by the BSC 32 as a result of being re^¬ flected back by the reference beam reflector 64 is directed by the BSC 32 towards the optical detector 95. The object beam 52 and the spatially filtered reference beam 54 pass through a third lens 76 arranged in a 4f configuration to the second lens 74. The object beam 52 and the spatially filtered reference beam 54 are superimposed at the optical detector 95 and form the interference pattern at the optical detector 95.

In the arrangement 1 of the present technique, since the ob- ject beam 52 results from both the collimated part i.e. the first part 4 of the light beam and the focused part i.e. the second part 5 of the light beam, the lateral resolution of the imaging is increased as a result of the role of numerical aperture of the condensing region 16 of the condenser lens 10, as explained hereinabove. Furthermore, as the spatially filtered reference beam 54 results from the collimated part i.e. the first part 4, and since the amount of collimated part in the light beam 2 is substantial as compared to a sim- pie biconvex lens condenser, the intensity of the spatially filtered reference beam 54 is high as desired. Thus a desired quality of interference pattern is obtained at the optical detector 95 having an increased lateral resolution as com- pared to a setup, shown in FIG 3, without the condenser lens 10 of the present technique.

Referring to FIG 9, in combination with FIGs 1 to 8, according to a third aspect of the present technique, a method 1000 for inspecting the sample 99 is presented. The light beam 2 from the illumination source 20 has the first wavefront 3. In the method 1000, in a step 100 the light beam 2 from the il^¬ lumination source 20 is shined onto the condenser lens 10. In the method 1000, the condenser lens 10 is same as the conden- ser lens 10 presented according to the first aspect of the present technique and particularly in reference to FIGs 1 to 8. The light beam 2 transmitted by the condenser lens 10 shines upon the sample 99. Thereafter, in a step 200 the light beam 2 transmitted by the condenser 10 and after inter- action with the sample 99 is received by the BSC 32. Subse^¬ quently, in a step 300 the light beam 2 so received is split, by the BSC 32, into the object beam 52 and the reference beam 54. Thereafter in the method 1000, in a step 400 spatial fil^¬ tering of the reference beam 54 is performed by the spatial filter 66. In the spatial filtering 400, object information is at least partially filtered out from the reference beam 54. Then, in a step 500 the spatially filtered reference beam 54 and the object beam 52 are directed towards the optical detector 95. Finally in the method 1000, in a step 600 the interference pattern is detected at the optical detector 95.

The interference pattern resulting from first part 4 of the light beam 2 that interacted with the non-condensing region 16 and then with the sample 99, and thus provides the spa- tially filtered reference beam 54 with a desired or suitable intensity, and the second part 5 of the light beam 2 that in^¬ teracted with the condensing region 16 and then with the sam- pie 99 helps in increased lateral resolution of detection in the method 1000, as explained hereinabove.

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.

Claims

Patent claims

1. A condenser lens (10) for shining a light beam (2) from an illumination source (20) onto a sample (99) to be inspected by an interferometric microscopy device (98), the light beam (2) from the illumination source (20) having a first wave- front (3), the condenser lens (10) comprising:

- a non-condensing region (12) configured to receive a first part (4) of the light beam (2) from the illumination source

(20) and to transmit the first part (4) of the light beam (2) so received towards the sample (99) such that the first part (4) of the light beam (2) so transmitted by the non- condensing region (12) has the first wavefront (3); and

- a condensing region (16) configured to receive a second part (5) of the light beam (2) from the illumination source (20) and to transmit the second part (5) of the light beam (2) so received towards the sample (99) such that the second part (5) of the light beam (2) so transmitted by the condens^¬ ing region (16) has a second wavefront (6), wherein the first wavefront (3) is different from the second wavefront (6) .

2. The condenser lens (10) according to claim 1, wherein the non-condensing region (12) and the condensing region (16) are adjoining each other and formed as a single physical entity (11) .

3. The condenser lens (10) according to claim 2, wherein the condensing region (16) peripherally surrounds the non- condensing region (12) .

4. The condenser lens (10) according to claim 3, wherein the non-condensing region (12) is flat disc shaped and the con- densing region (16) is annular in shape.

5. The condenser lens (10) according to claim 4, wherein the non-condensing region (12) is located centrally.

6. The condenser lens (10) according any of to claims 1 to 5, wherein the non-condensing region (12) comprises a hole (13) .

7. The condenser lens (10) according any of to claims 1 to 6, wherein the non-condensing region (12) and the condensing region (16) comprise a same transparent material.

8. An interferometric microscopy arrangement (1) for inspect- ing a sample (99) placed in a sample port (90) by shining a light beam (2) from an illumination source (20) onto the sample (99) and detecting an interference pattern at an optical detector (95), the light beam (2) from the illumination source (20) having a first wavefront (3), the interferometric microscopy arrangement (1) comprising:

- a condenser lens (10) optically positioned between the il^¬ lumination source (20) and the sample port (90), wherein the condenser lens (10) is according to any of claims 1 to 7; and

- an interferometric unit (30) positioned optically down^¬ stream of the sample port (90) and configured to receive the light beam (2) transmitted by the condenser lens (10) after interacting with the sample (99), wherein the interferometric unit (30) is further configured to generate from the light beam (2) so received an object beam (52) and a reference beam (54) and to direct the object beam (52) and the reference beam (54) towards the optical detector (95) to form the in^¬ terference pattern at the optical detector (95) by interac- tion of the object beam (52) and the reference beam (54) .

9. The interferometric microscopy arrangement (1) according to claim 8, comprising the illumination source (20) .

10. The interferometric microscopy arrangement (1) according to claim 9, wherein the illumination source (20) is configured to provide at least one of collimated light, coherent light and a combination thereof.

11. The interferometric microscopy arrangement (1) according to any of claims 8 to 10, wherein the interferometric unit (30) is configured to define an object beam path to direct the object beam (52) towards the optical detector (95) and a reference beam path to direct the reference beam (54) towards the optical detector (95) and wherein the object beam path substantially overlaps with the reference beam path, the interferometric unit (2) comprising:

- a beam splitter/combiner (32) configured to receive the light beam (2) transmitted by the condenser lens (10) and to split the light beam (2) so received into the object beam (52) and the reference beam (54);

- an object beam reflector (62) positioned in the object beam path and configured to receive the object beam (52) from the beam splitter/combiner (32) and to reflect the object beam

(52) back towards the beam splitter/combiner (32), and where- in the beam splitter/combiner (32) is further configured to direct the object beam (52) reflected back from the object beam reflector (62) towards the optical detector (95);

- a reference beam reflector (64) positioned in the reference beam path and configured to receive the reference beam (54) from the beam splitter/combiner (32) and to reflect the reference beam (54) back towards the beam splitter/combiner (32), and wherein the beam splitter/combiner (32) is further configured to direct the reference beam (54) reflected back from the reference beam reflector (64) towards the optical detector ( 95 ) ;

- a spatial filter (66) positioned optically in front of the reference beam reflector (64) and configured to at least par- tially filter object information from the reference beam (54) before the reference beam (54) is reflected back from the reference beam reflector (64); and - a reference beam Fourier optics assembly (70) comprising at least a first lens (72) arranged at 4f configuration to a se^¬ cond lens (74) .

12. The interferometric microscopy arrangement (1) according to claim 11, wherein the spatial filter (66) is a pinhole.

13. The interferometric microscopy arrangement (1) according to claim 11 or 12, further comprising an objective lens (80) configured to receive the light beam (2) after interaction with the sample (99) and wherein the first lens (72) is posi^¬ tioned such that a Fourier plane (82) of the objective lens (80) coincides with a focal plane (73) of the first lens (72) and wherein the spatial filter (66) is positioned at a other focal plane (77) of the second lens (74) .

14. The interferometric microscopy arrangement (1) according to any of claims 11 to 13, comprising a third lens (76) posi^¬ tioned at 4f configuration with respect to the second lens (74) .

15. A method (1000) for inspecting a sample (99) by shining a light beam (2) from an illumination source (20) onto the sample (99), the light beam (2) from the illumination source (20) having a first wavefront (3), the method (1000) compris^¬ ing :

- shining (100) the light beam (2) from the illumination source (20) onto a condenser lens (10), wherein the condenser lens (10) is according to any of claims 1 to 7, and wherein the light beam (2) transmitted by the condenser lens (10) shines upon the sample 99;

- receiving (200), by a beam splitter/combiner (32), the light beam (2) transmitted by the condenser and after interaction with the sample; - splitting (300), by the beam splitter/combiner (32), the light beam (2) so received into an object beam (52) and a reference beam (54); - spatial filtering (400) of the reference beam (54) by a spatial filter (66) wherein object information is at least partially filtered out from the reference beam (54);

- directing (500) the reference beam (54) so spatially fil- tered and the object beam (52) towards an optical detector

(95); and

- detecting (600) an interference pattern at the optical de^¬ tector (95) .

16. The method (1000) according to claim 15 wherein the light beam (2) is one of coherent light, collimated light, and a combination thereof.

17. The method (1000) according to claim 15 or 16, wherein at least one of the splitting (300) of the light beam (2), the spatial filtering (400) of the reference beam (54), the di^¬ recting (500) of the reference beam (54) so filtered and the object beam (52) towards the optical detector (95), and a combination thereof is performed within an interferometric unit (30), and wherein the interferometric unit (30) is ac^¬ cording to claim 11 or 12.