IL257633A - Pinhole mirror - Google Patents

Description

- 1 - 257633/3 PINHOLE MIRROR TECHNOLOGICAL FIELD AND BACKGROUND The present invention is generally in the field of light directing optics and relates to a pinhole mirror and method of its manufacture.

Pinhole mirrors are widely used in optical systems of various types. Typically, a pinhole mirror can be used in a measurement / inspection system as a field stop, defining a measurement area / site inside the illuminated spot.

More specifically, the optical system may include a light collection-detection assembly including an imager and a spectrophotometric detector / sensor. In this case, a beam splitter in the form of a pinhole mirror is used in the optical path of light returned (reflected or scattered) from the illuminated spot on a sample and propagating along a collection channel.

Pinhole mirror, although performing a beam splitting function is different from a typical beam splitter. A typical beam splitter, as described for example in JP2004279495, has a beam splitting surface of the same optical properties along the beam splitting surface. In a typical/classic beam splitter, incident light is split into spatially separated light components according to different optical properties of different light components of the incident light (e.g. wavelength and/or polarization), and/or different light incidence schemes.

The pinhole mirror spatially separates a central part of the beam reflected from the measured area inside the illuminated spot and allows its propagation towards the spectrophotometric detector, and directs a periphery part of the light beam towards the imaging detector. As a result, a measurement area of the illuminated spot, detected in the spectrophotometric detector, presents a "dark" central region in the field of view of the imaging detector. - 2 - 257633/3 Various optical schemes utilizing pinhole mirror are described for example in US 7,245,375; US 8,564,793; US 9,184,102; US 9,651,498, all assigned to the assignee of the present application.

GENERAL DESCRIPTION There is a need in the art for a novel approach in pinhole mirror configuration.

This is associated, for example, with the requirement for a high-quality pattern of the arrangement of reflecting-transparent-reflecting regions forming the pinhole. However, practically, the optical properties of both the transparent and mirror-reflecting regions degrade in time, mainly due to contaminations. This affects the light propagation through and out of the pinhole structure. Also, light passage through a typical pinhole mirror structure is associated with optical aberrations.

In a metrology system, it is common to use an optical system defining two spatially separated channels for collection/detection of portions of light returned from different regions of an illuminated / measurement spot. One such collection/detection channel may be associated with a spectrophotometric detector, and the other channel with an imaging detector. This approach is used in the metrology system in order to locate the measurement area in the entire illuminated spot defined by the field of view of the imaging detector. As described above, the separation of the light portions returned from central and peripheral portions of the illuminated spot is performed using a pinhole element.

In this connection, reference is made to Figs. 1A and 1B schematically illustrating the light propagation scheme in an optical system defining two output channels of different optical functions (e.g. measurement and imaging channels). As shown in Fig. 1A, a light beam B1 reflected from an illuminated spot/region on the article (not shown here) is focused by a lens onto a pinhole mirror plate P/H Mirror, while pinhole of the pinhole mirror plate is conjugate to the center of the illuminated region on the article. Pinhole mirror plate spatially separates between the central part B2 and peripheral part B of the light beam B which are, respectively, transmitted and reflected by the 3 1 regions of the pinhole mirror plate to a measurement/sensor device (e.g. spectrometer) via its associated sensor relay lens (spectrometer sensor relay SSR) - 3 - 257633/3 and a sensor fiber, and to an imaging device (e.g. CCD or CMOS camera) via its associated imaging lens (CCDR). As better seen in Fig. 1B, the imaging of the pinhole mirror onto the sensor fiber suffers from lateral chromatic and astigmatism aberrations.

This configuration also suffers from sensitivity to dust particles on mirror and inside pinhole.

Thus, the P/H Mirror has two main functions: it allows passage of light from relatively small field of view through a pinhole area / region (optically transparent region) to the sensor, and reflects light from larger field of view by reflective region to the imager.

Such operation of the pinhole mirror supports two optical channels operating with the pinhole mirror. These channels may be associated with different detection units, e.g. spectral measuring and imaging channels, having different optical requirements.

The present invention provides a novel pinhole mirror device, including an optical unit / enclosure and a light splitting element, such that at least a pinhole region of the light splitting element is fully embedded in the optical unit. The configuration of the pinhole mirror device of the invention provides for optimizing (maximizing) transmission / reflection of the respective region of the light splitting element towards the respective channel.

In some embodiments, the optical unit has a cube-like configuration. Therefore, the pinhole mirror device of the invention is at times termed hereinbelow as cube-inside pinhole or pinhole mirror in cube structure. It should, however, be noted, and will be exemplified further below, that the invention is not limited to a cubic geometry of the optical unit, as well as any other specific geometry of the optical unit, provided that at least the pinhole region of the light splitting element is fully embedded in the optical unit.

With regard to the pinhole region of the light splitting element, it should be noted that this region presents a central region of the light splitting element having first optical properties with respect to light incident thereon, and is surrounded by a second, peripheral region of the light splitting element having second optical properties, where the first and second optical properties are reflective (specular) and transmitting. As will be described further below, the central region may be optically transparent region surrounded by the peripheral mirror region; or the central region may be reflective (configured to direct incident light by total internal reflection or reflective feature) surrounded by peripheral - 4 - 257633/3 optically transparent region. It should thus be understood that the term “pinhole” or “pinhole region” as used hereinbelow should not be limited to transparent region / window.

According to one broad aspect of the invention, it provides a pinhole mirror device configured for spatially splitting light collected with a field of view of an optical system into different light channels associated with different optical functions, while optimizing transmission and reflection of the device, the pinhole mirror device comprising an integral structure comprising: an optical unit formed by first and second structures which are made of an optically transparent material for light of predetermined spectrum and are facing one another by their first and second substantially planar facets, respectively; and a light splitting element comprising a first central region having first optical properties surrounded by a second peripheral region of second different optical properties with respect to light of said predetermined spectrum, said light splitting element being located at an interface between said first and second facets, such that at least said first central region of the light splitting element is embedded in (located completely inside of) the optical unit.

In some embodiments, the first and second regions are substantially transmitting and substantially reflective, respectively, with respect to light of said predetermined spectrum. This can be implemented by applying reflective coating on the second region.

In some other embodiments, the first central region is a cavity configured to reflect light incident thereon by total internal reflection, while the second region is defined by the optically transparent interface between the two structures, e.g. optical contact.

The first and second structures are optically coupled to one another at said interface region, within the splitting element location.

In some embodiments, the first structure has a light input facet oriented with respect to the interface region such that said patterned surface faces the input facet, and an incident light beam entering the first structure through the input facet interacts with said patterned surface, such that propagation of central and peripheral parts of the light beam are differently affected by interaction with, respectively, the first and second regions of the light splitting element. In some embodiments, the light splitting element allows propagation of (transmits) the central portion of the incident light beam through - 5 - 257633/3 and out of the second structure substantially not affecting the direction of propagation of said central portion, and reflects the periphery portion of the incident light beam to propagate in an output direction through and out of the first structure. In some other embodiments, the first and second regions of the light splitting element on the respective central and peripheral portions of the light beam are vice versa.

Preferably, the central optically transparent region of the light splitting element has substantially elliptical geometry, configured/oriented such that a long axis of the ellipse is tilted with respect to an axis of the incident bream at a certain angle (e.g. an angle of 45 degrees). This provides projection of the elliptical optically transparent region onto a plane orthogonal to the incident beam axis has a substantially circular geometry.

The first and second structures may be configured as prisms. These may be right angle prisms, with the patterned surface being located at a hypotenuse contact surface between the prisms.

The first and second structures may be oppositely symmetric with respect to said interface. As indicated above, the first and second structures interfacing one another via said first and second substantially planar facets may form a substantially cubic geometry.

In some other embodiments, the first and second structures may have different geometries. For example, the first and second structures may be parts (e.g. halves) of first and second cubes of different dimensions. Generally, the configuration of the optical unit is preferably such that each of the facets intersecting the light propagation path is substantially orthogonal to the light propagation path.

As indicated above, the first and second structures are optically fixed / contacted to one another at the light splitting element. To this end, an optically transparent medium is applied between the first and second structures within the light splitting element. Such gluing medium is typically formed by dielectric material(s), e.g. liquid. The proper optical interface is provided by using the medium having a refractive index profile substantially matching a refractive index of the first and second structures for said predetermined spectrum.

In case of using liquid as a medium filling gap between the prisms, the peripheral area of the contact is to be sealed to prevent liquid leakage and evaporating. This is not required in case of using glue. - 6 - 257633/3 The patterned splitting element may be formed by applying a reflective coating on a respective region of either one of the first or second planar facets to form the second (peripheral) region of the light splitting element. Preferably, such reflective coating is provided on the planar surface of the first structure, i.e. the structure which faces the incident beam (located upstream of the other structure with respect to light propagation through the device).

The pinhole mirror device may be configured for use in optical systems operating in visible, NIR and UV spectral ranges, the first and second structures being thus made of the material transparent for light of 200-1000 nm spectra. Such structures may be made from UV Grade fused silica.

According to another broad aspect of the invention, it provides an optical system for use in measurements on an article, the optical system being configured for collecting a light response of an illuminated spot on the article with a field of view and directing the collected light to propagate along first and second spatially separated channels of different optical functions associated with, respectively, first and second light receiving devices, said optical system comprising the above described pinhole mirror device, wherein a center of the light splitting element is conjugate to a center of the illuminated spot.

The receiving device may be constituted by a light detector or / and a light receiving optics (e.g. lens unit; fiber). The optical system further includes a focusing unit located in an optical path of light propagation though the system upstream of the pinhole mirror device such that a center of the optically transparent region is located at a focal spot of the focusing unit. The optical system may include relay optics located at the first and second channels.

The invention in its yet further aspect provides a measurement system for measuring properties of a sample, the measurement system comprising the above described optical system, and the first and second light receiving devices comprising, respectively, a measurement device and an imaging device accommodated at first and second light output channels.

The inventors have shown that the technique of the invention provides for “screening” the pinhole mirror itself (light splitting element) from dust particles. Such particles can only fall on exposed surfaces of the device and thus do not result in sharp - 7 - 257633/3 images, formed by light reflected from the periphery regions of the pinhole mirror or reducing measured signal due to blocking pinhole area. Also, the device of the present invention provides for decreasing lateral chromatic aberration, and provides for avoiding astigmatism effects (existing in the conventional approach due to light passage through tilted pinhole plate).

BRIEF DESCRIPTION OF THE DRAWINGS In order to better understand the subject matter that is disclosed herein and to exemplify how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which: Figs. 1A and 1B schematically illustrate a typical light propagation scheme in an optical system utilizing a pinhole mirror defining two output channels of different optical requirements (e.g. measurement and imaging channels); Fig. 2 is a schematic illustration of an optical system utilizing a pinhole mirror device according to an example of the present invention; Fig. 3 more specifically illustrates a light propagation scheme of the pinhole mirror device according to an example of the present invention; Fig. 4A exemplifies the geometry of the (optically transparent) region, corresponding to FOV of the measurement channel, in the pinhole mirror device of the present invention; Fig. 4B more specifically illustrates an example of the configuration of the light splitting element (patterned surface/film) defining the optically transparent region of the geometry of Fig. 5A, on the interfacing facet of one of the structures forming the pinhole mirror device of the present invention; Figs. 5A and 5B more specifically illustrate two examples of the light splitting element in the pinhole mirror device of the present invention providing optical coupling between the two optically transparent structures (prisms); - 8 - 257633/3 Figs. 6A and 6B exemplify light propagation scheme in a pinhole mirror device utilizing an inverted configuration, in which the light splitting element reflects the central portion of an incident light beam and transmits the peripheral portion of the light beam; Figs. 7A and 7B show a few more examples of different geometries (shapes and sizes of the pair of optically transparent structures (prisms) with the light splitting element between them) having various optical features; and Figs. 8A and 8B show an example of an optical system utilizing the exemplary pinhole mirror device of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS Figs. 1A and 1B show schematically an optical system utilizing a conventional pinhole mirror plate. As described above, with such pinhole mirror plate, the optical properties of both the transparent and reflective regions of the pinhole element degrade in time (mainly due to contamination), thus affecting the light propagation through and out of the pinhole structure resulting in the change of the collected light. Contamination negatively affects the performance of metrology system, e.g. decreases the performance of a pattern recognition process carried out by an imaging device (which is associated with / is a part of a pattern recognition sub-system) for navigating measurement/metrology measurement area on an article (e.g. wafer), and/or decreases the measured signal by full or partial blocking of the pin-hole. Cleaning the device from contaminations / particles, and especially cleaning pinhole, is a cumbersome procedure, which may even damage the device and should therefore be avoided.

Referring to Figs. 2 and 3, there is schematically illustrated an example of an optical system 10 utilizing a pinhole mirror device 12 of the present invention, and the configuration and operation of the pinhole mirror device 12. To facilitate illustration and understanding, the same reference numbers are used to identify components that are common in all the examples of the invention.

It should be understood, although not specifically shown, that the optical system may be part of a measurement (e.g. metrology) and/or inspection system configured for measuring parameters/properties of a sample. Such measurement system typically includes an illumination unit defining an illumination channel for directing light to - 9 - 257633/3 illuminate a spot/region on the sample, and a detection assembly, which is a part of collection channel for collecting light returned from the illuminated spot/region corresponding to the collection field of view and directing the collected light to one or more detectors. Both the illumination and the collection channels include optical elements, e.g. lenses, fibers, etc.

Fig. 2 schematically illustrates a light propagation scheme in the optical system associated with the detection assembly, i.e. a light collection channel Ccoll of a measurement/metrology system. The optical system 10 thus defines a light input path Cin for light coming from an illuminated spot/region (not shown), and first and second light (1) (2) output paths C and C associated with, respectively, first and second light out out receiving devices 20 and 22, and includes the pinhole mirror device 12 configured and operable according to the present invention.

The receiving devices 20 and 22 are associated with different detection units 23 and 25. The detection unit 23 and 25 may be associated with their respective optical elements. For example, the first detection unit 23, which may include an imaging detector (e.g. CCD) is associated with its imaging optics 17 (comprising one or more lens elements, e.g. relay lens unit), and the second detection unit 25, which may include a measuring / sensing detector (e.g. spectrometer) is associated with its relay lens unit 19 and possibly also an optical fiber 21 operating as a spectrometer slit. As indicated above, the imaging detector may be associated with (be a part of) a pattern recognition system, and the other detection unit 25 is associated with a measurement (spectrometric) channel.

As shown more specifically in Fig. 3, the pinhole mirror device 12 is configured as an integral optical unit 24 formed by first and second structures 14 and 16 made of an optically transparent material for light of predetermined spectrum at which the system operates, and a light splitting element 18 at an interface between the structures 14 and 16.

The interface is formed by substantially planar facets 14A and 16A of the structures 14 and 16. As will be exemplified more specifically further below, the optically transparent structures 14 and 16 are optically coupled one to another at region(s) of the light splitting element 18.

The light splitting element 18 is formed by a patterned surface defining first central region 18A of first optical properties (e.g. an optically transparent region for light - 10 - 257633/3 of the predetermined spectrum) surrounded by a second peripheral surface region 18B of second different optical properties (e.g. reflective (mirror region)) for light of the spectrum used in the imaging channel. Such patterned surface may be part of any one of the planar facets 14A and 16A. Preferably, facet 14A is configured as an “internal” reflective surface. The system configuration is such that the center of the element 18 is located in the image plane of the illuminated spot/region on the article.

The optically transparent structures 14 and 16 forming the optical unit 24 may be configured as prisms. If the input and output facets of the prisms are perpendicular to the beam axes, that is preferable to minimize chromatic aberration due to prism substrate material dispersion. As shown in the specific but not limiting example of these figures, the optical unit 24 of the pinhole mirror device 12 has a cubic shape, i.e. the structures 14 and 16 are right angle prisms identically symmetrical with respect to the interface 14A- 16A between them being a diagonal plane of the cube. It should, however, be noted, and will be exemplified further below, that the structures 14 and 16 may have different geometries (shapes and/or dimensions).

The first structure 14 has a light input facet 14B. An input light beam L (e.g. formed by light returned from the illuminated spot on the sample) while being focused onto the pinhole element 18 whose center is at the image plane of the illuminated spot/region on the article, propagates in an input propagation direction, enters the first structure via this facet 14B and continuous its propagation in the input propagation direction inside the first structure 14 to interact with the patterned surface 18. In the present not limiting example, the light splitting element 18 has the central pinhole region 18A which is optically transparent and the peripheral region 18B which is a mirror region.

At the patterned surface 18, the light beam L is spatially split into first and second light beams L1 and L2 thereof being, respectively, the portions of the beam L interacting with the peripheral (reflective) region 18B and central (optically transparent) region 18A of the patterned surface 18. The central light component L is transmitted in the input 2 propagation direction through and out of the second structure 16, and the peripheral rays L of the input beam L are reflected to propagate in an output direction, different from 1 (e.g. orthogonal to) the input propagation direction, through and out of the first structure via its output facet 14B. Thus, central and peripheral light components L1 and L2 of the input light beam L are output from the pinhole mirror device 12 and propagate along the - 11 - 257633/3 (1) (2) output paths C and C associated with, respectively, first and second light out out receiving devices 20 and 22. Light input and output facets 14B and 14C are preferably coated with anti-reflective coatings to maximize transmission of the optical unit 24.

It should be understood that, alternatively, facet 14C can serve as a light input facet, and facets 16C and 14B would be output facets, for respectively, transmitted and reflected light portions. In this case, facet 14C also preferably has anti-reflective coating.

The optical system 10 may include various optical elements. As exemplified in Fig. 2, the optical system 10 includes a focusing unit (one or more lenses) 15 located in the input path C upstream of the pinhole mirror device 12 and accommodated such that in a center of the optically transparent region 18A is located at a focal point of the focusing lens 15.

Thus, in this example, the beam L2, returned from the illuminating spot/region (2) and corresponding to the field of view of the measuring channel C out (being a part of the total field of view of the collection optics) enters the device 12 through facet 14B of the first prism 14, is focused on the center of the light splitting element (where the light transmitting region 18A is located) on the diagonal side 14A-16A of the cube 12, passes through transmitting region 18A towards the prism 16, and exits this prism via the facet 16B thereof. The beam L , returned from the illuminated spot/region and collected with 1 the field of view of the collection optics enters the device 12 through the same input facet 14B of the first prism 14, incident on the diagonal side 14A-16A of the cube 12, is reflected by reflective region (e.g. annular region) 18B and exits the prism 14 via its orthogonal facet 14B.

Pinhole mirror device 12 thus transmits the light from the field of view of the article corresponding to the central optically transparent region 18A to the (2) measurement/sensing channel C out to be received/detected by the measurement detector, and reflects light from a relatively large field of view by region 18B to the (1) imaging channel C to be received/detected by the imaging detection unit having out optical requirements different from those of the measuring channel detector.

Figs. 4A and 4B illustrate more specifically an example of the geometry of the pattern defining the light splitting element 12. As shown in Fig. 4A, the optically transparent region 18A is preferably of a substantially elliptical geometry. It should be - 12 - 257633/3 understood that the use of the elliptical geometry of region 18A (as alternative to substantially circular geometry) allows proper orientation of the ellipse 18A such that a long axis a of the ellipse is tilted with respect to the incident beam axis at a certain angle (e.g. an angle of 45 degrees). This provides a projection of the elliptical optically transparent region 18A onto a plane orthogonal to the incident beam axis of a substantially circular geometry.

Reference is made to Figs. 5A and 5B exemplifying physical and optical coupling between the first and second optically transparent structures (prisms) 14 and 16 enclosing the light splitting element therebetween. In both examples, the reflective region 18B is formed preferably by reflective coating (film) 30 on the planar facet 14A of prism 14.

The structures 14 and 16 may be both fused silica physically coupled one to another via a filling medium 28 located between facets 14A and 16A within at least a part of the region of the light splitting element 18. The bonding medium 28 may be applied, during adhesion, on either one or both of the facets 14A and 16A of prisms 14 and 16. In the example of Fig. 5A, the medium 28 is a single layer or may be a refractive index matched liquid, for example Cargille 30350. In the example of Fig. 5B, the two-layer structure of adhering medium 28 is shown using CV15-2500.

The liquid medium 28 is optically transparent such that a region 28A of the medium 28 in the region 18A provides optical coupling between the prisms 14 and 16.

Proper optical coupling between the prisms 14 and 16 is provided by using medium (liquid) 28 having a refractive index matching (or almost matching) over operational spectral range to refractive index of the substrate material of the prisms 14 and 16 for the predetermined spectral range for which the device 10 is designed. Considering the use of liquid 28 such as Cargille 30350 between the fused silica prisms, the refractive index of the liquid is similar to fused silica, i.e. is from 1.54 at 225 nm to 1.45 at 1000 nm, while the difference from that of fused silica is below 0.02 at any wavelength inside the operation spectral range. As for filling medium CV15-2500, the refractive index difference from that of fused silica is below 0.015.

Reference is made to Figs. 6A and 6B showing an alternative configuration of a pinhole mirror device 12 utilizing an inverted configuration. In this example, the light splitting element 18 is formed by an etched pinhole region 18A on an interface 14A-16A (e.g. the diagonal plane of the cubic structure) formed by optically transparent prisms 14 - 13 - 257633/3 and 16. The prisms 14 and 16 are thus optically coupled along the diagonal interface except for the pinhole area 18A. Here, peripheral portion L1 of an incident light beam L, corresponding to the full field of view except for a small area in the center, defined by 18A, passes through the diagonal interface maintaining the input light propagation direction, while the central portion L2 of the light beam L, corresponding to the measurement channel field of view and defined by the pinhole area 18A, is reflected due to the total internal reflection on the etched pinhole region 18A.

As described above, the structures 14 and 16 may not be of the same shape, as well as may not be of the same dimensions. In the above-described examples, the general cubic geometry of the device was illustrated. Referring now to Figs. 7A and 7B, pinhole mirror devices are exemplified, in which the first and second interfacing structures 14 and 16 are of different shapes (Fig. 7A), and the first and second interfacing structures 14 and 16 are of similar shapes but different dimensions (Fig. 7B). Also, in this example, the two structures 14 and 16 have different sizes of interfacing facets 14A and 16A, such that the two structures are only partially interfacing with one another. Although in these examples the central pinhole region as shown as being optically transparent surrounded by peripheral mirror (reflective) region, it should be understood that embodiments of such non-identical structures 14 and 16 can be used with the reflective pinhole region surrounded by optically transparent regions (as described above with reference to Figs. 6A-6B). In this case the mutual interface surface 18 limits the maximal field of view for the imaging channel.

Reference is made to Figs. 8A and 8B, which exemplify an optical system 100 utilizing a pinhole mirror device 12 of the present invention. The system 100 is generally similar to the system 10 exemplified in Fig. 2. It should be understood that system 100, as well system 10, illustrates the light propagation scheme along a collection detection channel, i.e. propagation of light returned from the illuminated spot/region. Similarly to the above-described system 10, in system 100 the center of the light splitting element 18 is conjugate to the center of the illuminated region.

The optical system 100 includes/defines a light input path/channel C , the pinhole in (1) (2) mirror device 12, and light output channels C and C associated with first and out out second receiving devices 20 and 22. In the example of Figs. 8A-8B, in distinction to the example of Fig. 2, the output of the pinhole mirror device 12 defined by input light - 14 - 257633/3 interaction with the central region 18A of the light splitting element 18 is directly optically coupled to the detection unit 25. Preferably, the configuration is such that the respective output facet 16B of the device 12 is integrated (assembled) with receiving device 22. The detection units 23 and 25 may include, respectively, an imaging device (e.g. CCD) and its associated imaging lens 17, and a measurement sensor. In the present example, the measurement sensor device is configured as a spectrometer, and includes a dispersing element (e.g. grating). As indicated above, the imaging detector 23 may be associated with (be a part of) a pattern recognition system.

Also, in the present example of Figs. 8A-8B, the optical system 100 could also include a reference channel C for a reference light beam L’, which is typically used for ref sampling the parameters of a light source, e.g. light intensity or spectral distribution. The operational principles of controlling the light intensity using the reference light beam are generally known and are not part of the present invention, and therefore need not be specifically described, except to note that the reference beam L’ from the reference channel Cref interacts with the peripheral (reflective) region 18B of the light splitting element onto the sensor device 25.

It should be understood that, although the cube-type optical housing of the pinhole mirror device is illustrated in this example, the invention is not limited to this specific geometry of the optical housing, and any other suitable geometry can be used, e.g. as those described above, provided at least the pinhole region 18A is fully embedded in the optical housing.

Thus, the present invention provides a novel pinhole mirror device which can advantageously be used in various optical systems, in particular the systems utilizing two light detection channels having different optical requirements, while the channels are split by their field of view.

Claims (24)

- 15 - 257633/3 CLAIMS:

1. A pinhole mirror device configured for spatially separating light collected with a field of view of an optical system into different light components to propagate along first and second spatially separated light channels associated with different optical functions, 5 the pinhole mirror device comprising an integral structure comprising: an optical unit formed by first and second structures which are made of an optically transparent material for light of a predetermined spectral range and are facing one another by their first and second planar facets, respectively; and a light splitting element comprising a first central region having first optical properties surrounded by a second peripheral region of second 10 different optical properties with respect to light of said predetermined spectral range, said light splitting element being located at an interface between said first and second facets, such that said first central region and at least a part of said second peripheral region of the light splitting element are embedded in said optical unit thereby forming said integral structure. 15

2. The pinhole mirror device according to claim 1, wherein said light splitting element is entirely embedded in said optical unit.

3. The pinhole mirror device according to claim 1 or 2, wherein the first and second regions are transmitting and reflective, respectively, with respect to light of said predetermined spectral range. 20

4. The pinhole mirror device according to claim 1 or 2, wherein the first and second regions are reflective and transmitting, respectively, with respect to light of said predetermined spectral range.

5. The pinhole mirror device according to any one of the preceding claims, wherein the first structure has a light input facet oriented with respect to said interface region such 25 that an input light beam entering the first structure via said light input facet from an input propagation direction continuously propagates with said input propagation direction inside the first structure to said light splitting element, such that propagation of central and peripheral portions of the light beam are differently affected by interaction with, respectively, the first and second regions of the light splitting elements, to output the 30 central and peripheral portions in differently oriented output directions. - 16 - 257633/3

6. The pinhole mirror device according to any one of the preceding claims, wherein each of facets of the first and second structures which is located in a light propagation path is oriented orthogonally to the light propagation path.

7. The pinhole mirror device according to any one of claims 3 to 6, wherein said 5 optically transparent region has an elliptical geometry with a long axis of an ellipse being tilted with respect to an optical axis at a certain angle, such that a projection of the elliptical optically transparent region on a plane orthogonal to the optical axis has a circular geometry.

8. The pinhole mirror device according to any one of the preceding claims, wherein 10 said first and second structures are configured as prisms.

9. The pinhole mirror device according to claim 8, wherein said light splitting element is located at a hypotenuse contact surface between the prisms.

10. The pinhole mirror device according to any one of the preceding claims, wherein said first and second structures are oppositely symmetric with respect to said interface. 15

11. The pinhole mirror device according to any one of the preceding claims, wherein said first and second structures interfacing one another via said first and second planar facets form a cubic geometry of the optical housing.

12. The pinhole mirror device according to any one of claims 1 to 9, wherein said first and second structures have different geometries. 20

13. The pinhole mirror device according to any one of the preceding claims, wherein the first and second planar facets are adhered one to another along a part of said light splitting element.

14. The pinhole mirror device according to claim 13, wherein an optically transparent adhering medium is located at said interface within the region of said light splitting 25 element, and the reflective region comprises a reflective coating on a peripheral region of the adhering medium leaving an uncoated central region of the adhering medium forming said central optically transparent region of said light splitting element surrounded by the reflective region of the light splitting element. - 17 - 257633/3

15. The pinhole mirror device according to any one of the preceding claims, wherein said first and second planar facets are fixed one to another at the optically transparent region of the light splitting element.

16. The pinhole mirror device according to any one of the preceding claims, wherein 5 said first and second structures are made of the material transparent for light of 200-1000 nm spectra.

17. The pinhole mirror device according to claim 15, wherein the first and second structure are made from UV grade fused silica.

18. The pinhole mirror device according to any one of the preceding claims, wherein 10 said light splitting element comprises a medium having a refractive index profile matching a refractive index profile of said optically transparent material of the first and second structures for said predetermined spectral range, thereby providing optical coupling between the first and second structures for light of the predetermined spectrum.

19. The pinhole mirror device according to any one of claims 14 to 18, wherein said 15 medium comprises liquid.

20. The pinhole mirror device according to claim 18 or 19, wherein said medium comprises a dielectric medium.

21. The pinhole mirror device according to any one of the preceding claims, wherein said reflective region is formed by a reflective coating on a respective region of either one 20 or both of the first and second planar facets.

22. An optical system for use in measurements on an article, the optical system being configured for collecting a light response of an illuminated spot on the article with a field of view and directing the collected light to propagate along first and second spatially separated channels of different optical functions associated with two receiving devices, 25 respectively, said optical system comprising the pinhole mirror device of any one of the preceding claims, wherein a center of the light splitting element is conjugate to a center of the illuminated spot. - 18 - 257633/3

23. The optical system according to claim 22, comprising a focusing unit located in an optical path upstream of the pinhole mirror device such that a center of the optically transparent region is located at a focal point of said focusing unit.

24. A measurement system for measuring properties of a sample, the measurement 5 system comprising the optical system according to claim 22 or 23, and said two light receiving devices comprising a measurement device and an imaging device accommodated at first and second light output channels.