Perforated disc for selecting light for optical imaging

Description

Technical field

[0001] The present invention relates generally to the technical field of optical imaging using pinhole apertures. In particular, the present invention relates to a (rotatable) perforated disk with a plurality of openings and optical passages, which can be introduced as small pinhole apertures into the beam path of an optical imaging system. Furthermore, the present invention relates to an optical imaging system with such a pinhole disk. Background of the invention

[0002] In the field of optical image transmission, rotating perforated disks are regularly used to enable sharp imaging in a precisely defined distance plane. Examples of such perforated disks are so-called "Nipkow disks" or "multi-pinhole disks." To enable three-dimensional imaging of a surface, individual surface layers must first be physically separated and recorded. These layers are then combined into 3D surface topographies using data processing techniques. Different surface layers can be captured by appropriately varying the distance between an optically detected object and at least part of a corresponding optical measurement system, with a perforated disk representing a component of the optical imaging system of this measurement system.

[0003] In confocal 2D and 3D microscopes, aperture discs serve to block out light reflected from the surface being imaged, acting as a dynamic aperture. This filtering of light falls outside a defined focal area of ​​the imaging system. Such spatial filtering of the reflected light allows for the creation of defined cross-sectional images of a surface, which can then be combined to form a 3D surface topography.

[0004] Perforated discs are typically made of an optically transparent material, such as glass, coated with a reflective layer. This reflective layer contains openings, each representing a pinhole. This reflective layer regularly emits stray light, which is reflected back from the disc itself, not from the object under investigation, and strikes a light detector, which detects the so-called "useful light." The useful light is the light reflected back from the object under investigation and intended for analysis. In unfavorable cases, the stray light can be orders of magnitude more intense than the useful light. In such cases, it becomes difficult or even impossible to scan the surface of the object under investigation with acceptable accuracy.Furthermore, a perforated disk made of an optically transparent material in the beam path represents a plane-parallel plate, which leads to optical displacement and thus geometric aberrations for all non-perpendicular incident rays. Additionally, chromatic aberrations also occur (due to dispersion of the optically transparent material). Moreover, reflections also occur at the optically transparent material itself, so that the transmission through such a perforated disk is less than 100%, because light intensity is lost as a result of such reflections.

[0005] The apertures of the pinholes are usually arranged on concentric circles, their polar angles following a statistical distribution as described, for example, in WO 2007 121706 A1. Alternatively, the apertures can be spatially distributed on logarithmic spirals, with one origin of the distribution located at the center of the pinhole disk. However, an arrangement of the apertures on concentric circles leads to visible rings in the optical image, while an arrangement on logarithmic spirals produces a decrease in light intensity towards the edge of the image.

[0006] To avoid unwanted reflections on the perforated disc, which can overpower the useful light, two approaches are regularly used. (A) One approach is to tilt the perforated disk in the optical beam path by an angle sufficiently different from 90°. The reflected stray light then takes a different path than the useful light and can be coupled out of the beam path. An undesirable consequence of such tilting is that all optical elements in the corresponding imaging system must be tilted, which in turn results in an asymmetry of the optical image and therefore leads to further geometric and chromatic aberrations. (B) A second approach is to use so-called polarization optics to reduce reflections, either as an alternative or in combination with the first approach.In this process, the light is polarized such that the polarization of the reflections from the perforated disk is perpendicular to the polarization of the useful light, which is reflected back from the surface being measured into the imaging system and detected by a light detector. A polarization filter can be used to suppress components of the stray light originating from the reflections at the perforated disk. However, this polarization-based approach is limited in its effectiveness because it assumes that the entire image is polarization-preserving. Since this assumption is not entirely true, only a portion of the stray light can be suppressed.

[0007] A known perforated disc with an absorbing coating is known from publication WO 2017 / 064629 A1.

[0008] The invention is based on the objective of creating a perforated disk which does not lead to imaging errors in optical imaging and avoids stray light generated by reflections and / or scattering at the perforated disk. Summary of the invention

[0009] This problem is solved by the subject matter of the independent claims. Advantageous embodiments of the present invention are described in the dependent claims.

[0010] According to a first aspect of the invention, a perforated disk for selecting light for optical imaging, in particular for optical imaging in a confocal imaging system, is described. The described perforated disk comprises an optically absorbing material having an absorption coefficient of at least 98%, wherein at least one recess is provided in the optically absorbing material, defining an optical passage through the perforated disk.

[0011] The described perforated disc is based on the understanding that by using a material with a very high absorption coefficient, unwanted reflections at the surface of the disc (outside the opening) can be largely reduced. This effectively avoids the disadvantages of known perforated discs described above. In particular, the light striking the disc outside the at least one opening is absorbed so strongly that tilting the disc and / or using polarizing optics to prevent stray light is unnecessary, because only an extremely small amount of light is reflected or backscattered at the surface of the material. The term "small amount of light" refers to the intensity of the unabsorbed light or radiation.

[0012] According to the invention, the majority of the light incident on the perforated disk (outside the opening) is absorbed. This means that the unabsorbed portion either passes through (transmits) the optically absorbing material and / or is (back)scattered at the surface of the material. Since transmission of light (outside the opening) is even more detrimental to most optical imaging than back reflection or backscattering, it is preferable to ensure that the transmission coefficient of the optically absorbing material is as low as possible. A transmission coefficient of at least approximately zero can be easily achieved if the optically absorbing material has a sufficient (layer) thickness.

[0013] The physical parameters described above—absorption coefficient A, transmission coefficient T, and reflection or backscattering coefficient R—all relate to the intensity of the corresponding light components. As is well known, the following relationship applies due to the physical law of conservation of energy: A + R + T = 1

[0014] In most applications, the described perforated disc must be placed in the beam path of an illumination light and / or a measuring light and rotated there in such a way that at least one opening allows individual light beams to pass through for a short time. For the purpose of defined rotation, the perforated disc can therefore have a shaft or be attached to a shaft and / or have a central opening that can be fixed to a rotatable shaft. The shaft or the opening is preferably located exactly in the center of the perforated disc so that, using a suitable drive system, it can be rotated about a defined axis of rotation without mechanical imbalance.It can be rotated so that different passages enter the beam path of an optical imaging system one after the other, each allowing only certain light rays of a beam to pass through for a short time (and blocking other light rays of the beam by means of absorption).

[0015] Preferably, the perforated disc has a plurality of recesses, at least some of which are arranged at different radial distances from the center of the disc. This allows an object to be detected by rotating the perforated disc in a known manner, not only along a (curved) line, but also at multiple measuring points in a two-dimensional area.

[0016] In this document, the term "illumination light" refers to those light rays emanating from a light source that strike the object to be detected, either directly or indirectly (via at least one further optical element such as a lens or a mirror). In contrast, this document uses the term "measuring light" for those light rays that are backscattered from the object to be detected and strike a suitable light detector, either directly or indirectly.

[0017] According to the invention, the perforated disk further comprises a substrate, wherein the optically absorbing material is a coating on the substrate. This has the advantage that the optically absorbing material can be easily realized in a suitable three-dimensional physical structure. The coating can, for example, be produced by suitable chemical and / or physical vapor deposition.

[0018] According to a further embodiment of the invention, the substrate is an optically transparent substrate.

[0019] An optically transparent substrate as a base material for a coating applied to it can be particularly advantageous in the production of the described perforated disc. The at least one recess in the optically absorbing material can be created during coating application by at least one suitable covering structure, which ensures that no optically absorbing material is cut off at the relevant point.

[0020] In this context, optically transparent can mean transmittance to one or more wavelengths of a light spectrum, whereby this light spectrum is not necessarily limited to the visible light spectrum. In particular, the optically transparent substrate can alternatively or in combination with transmittance to visible light also be transparent to infrared radiation and / or ultraviolet radiation. According to a further embodiment of the invention, the substrate comprises a semiconductor material.

[0021] The use of a semiconductor material can be particularly advantageous for perforated disks that require high-precision manufacturing to achieve high optical imaging accuracy. This semiconductor material can, for example, originate from a wafer, which is typically used for the production of semiconductor devices.

[0022] According to a further embodiment of the invention, the semiconductor material is silicon. This has the advantage that the substrate can be manufactured particularly cost-effectively and / or purchased from a manufacturer of the perforated disk. Silicon is a material that is also used in many other applications, particularly in the field of electronics manufacturing, and is therefore widely available and of high quality.

[0023] According to the invention, the substrate has a through-opening in the area of ​​at least one recess.

[0024] A through-hole is particularly advantageous, or even necessary, for substrates that are at least partially optically absorbent. However, a through-hole can also be useful for optically perfectly transparent substrate materials because even 100% transparent materials exhibit a reflection coefficient at the air-substrate interface, due to the differences in refractive indices between air and substrate, even with perpendicular light incidence. This reflection coefficient is not negligible in practice.

[0025] According to a further embodiment of the invention, the through-opening has a cross-sectional area that changes continuously or discretely or in steps along a direction parallel to a normal vector of the perforated disk. The described direction defines, in particular, a thickness of the perforated disk or the substrate of the perforated disk.

[0026] The described continuous change in the aperture cross-section can be so pronounced that at least one side wall of the aperture is inclined so steeply relative to the surface of the perforated disc that no unwanted clipping (vignetting), reflections, or scattering of light rays passing through the corresponding opening of the perforated disc occurs at this side wall. Since such "side wall scattering" can also make a significant contribution to stray light, the optical quality of the perforated disc can be improved by using suitable apertures that deviate from a pure cylindrical shape.

[0027] According to a further embodiment of the invention, the through-opening has the shape of a truncated cone. Designing the (at least one) through-opening in the shape of a truncated cone has the advantage that the through-opening can be easily and accurately introduced into or formed in the substrate.

[0028] Preferably, frustoconical or cone-shaped through-holes can be formed by laser drilling. Alternatively or in combination, etching processes, known, for example, from semiconductor technology, can also be used to create the at least one through-hole.

[0029] According to a further embodiment of the invention, the at least one recess has a width between 1 µm and 30 µm, and in particular a width between 2 µm and 10 µm (1 µm = 10⁻⁶ m). Recesses of this spatial dimension are particularly advantageous for optical measuring systems operating in the visible and / or infrared spectral range. The advantage of the described spatial dimensioning lies particularly in the fact that the recesses are large enough to almost completely avoid undesirable diffraction effects. Furthermore, suitably dimensioned recesses allow for a good compromise between (a) spatial resolution of the light beam selection and (b) a sufficiently high intensity of light that can pass through or penetrate the recess. This sufficiently high light intensity can refer to both illumination and measurement light.

[0030] The term "width of the recess" refers specifically to a direction parallel to the surface or perpendicular to the surface normal vector of the perforated disk. Furthermore, the term "width" can refer to various cross-sectional shapes. In the case of a circular cross-section, the term "width" refers to the diameter of the circle. In the case of an elliptical cross-section, the term "width" refers either to the semi-minor axis or the semi-major axis of the ellipse. In the case of a rectangular cross-section, the term "width" can refer to any of the side lengths of the rectangle. Similar or corresponding considerations apply to the meaning of the term "width" for other cross-sectional shapes, such as those formed by a polygon.

[0031] According to a further embodiment of the invention, the absorption coefficient is greater than 99%, in particular greater than 99.5% and further in particular greater than 99.95%.

[0032] Since the intensity of stray light decreases with increasing absorption, a correspondingly high or even higher absorption coefficient leads to a further improvement of a measuring system incorporating the described perforated disk. A sufficiently high absorption coefficient can be achieved, for example, by using a black material with a high surface roughness. Such a material contains, for instance, carbon, which is applied to the substrate of the perforated disk in the form of carbon black.

[0033] According to a further embodiment of the invention, the optically absorbing material comprises carbon nanotubes. Carbon nanotubes can be advantageously used to realize an optically absorbing material with a particularly high absorption coefficient.

[0034] According to a further embodiment of the invention, (at least a large proportion of) the carbon nanotubes are aligned along a preferred direction, wherein the preferred direction is oriented in particular parallel to a normal vector of the perforated disk. The absorption coefficient of the optically absorbing material can be further increased by using carbon nanotubes oriented in this way.

[0035] According to a further embodiment of the invention, the perforated disk further comprises at least one further recess, wherein the further recess defines a further optical passage which is larger than the optical passage which is defined by the aforementioned and introduced recess.

[0036] The optical apertures of varying sizes can be distributed statistically or uniformly over at least a larger portion of the aperture disk or over the entire disk. Alternatively, optical apertures of varying sizes can be assigned to different portions of the disk. In this way, the described aperture disk can provide different spatial resolutions for optical imaging.

[0037] According to a further embodiment of the invention, a plurality of optical passages are provided which have different radial distances with respect to a center point of the perforated disk, wherein (a) for a first radial distance, two adjacent first optical passages have a first angular distance with respect to the center point, and (b) for a second radial distance, two adjacent second optical passages have a second angular distance with respect to the center point. If the first distance is greater than the second distance, then the first angular distance is smaller than the second angular distance.

[0038] To put it simply, the numerous optical paths are not arranged on (half)lines extending radially outwards from the center point or in a star-like pattern outwards, where the angular distance between any two adjacent lines is equal. In such a case, the distance between two adjacent optical paths, which have at least approximately the same radial distance from the center point, would be greater for larger radial distances. However, this need not be the case in the embodiment described here, because, to put it simply, a first circle around the center point with a first radius has a greater number of optical paths than a second circle around the center point with a second radius, which is smaller than the first radius.

[0039] In this document, the term "angular distance" between two adjacent optical passages with the same radial distance to the center means the angle enclosed between (i) a first (half) line extending from the center to one of the two optical passages and (ii) a second (half) line extending from the center to the second of the two optical passages.

[0040] The "non-star-shaped" spatial distribution of the optical passes described here can have the particular advantage that, without a loss of spatial resolution, a larger amount of light is "collected" for larger radial distances during one revolution of the perforated disk, so that optical measurement signals with a large signal-to-noise ratio can be recorded by a light detector.

[0041] According to a further embodiment of the invention, the optical paths are spatially distributed across the perforated disk in such a way that an at least approximately equal signal-to-noise ratio can be achieved over a predetermined field of view of the confocal optical imaging. This improves the ability of an optical imaging system to reliably detect (quantitatively) surface areas of the object that exhibit differing reflection properties. Local adjustment or modification of the illumination intensity is then unnecessary.

[0042] To achieve a particularly uniform signal-to-noise ratio, the number of optical passes occurring at a specific radial distance from the center of the perforated disk can be proportional to that radial distance. This can mean that, at a constant rotational speed of the perforated disk, the frequency distribution of the optical passes as a function of the radial distance is a straight line with a positive slope.

[0043] According to a further embodiment of the invention, the perforated disk further comprises at least one optical window which is large enough that at least a partial area of ​​an object to be detected can be optically imaged through the optical window onto a camera, wherein the imageable partial area of ​​the object is larger than an area of ​​the object which can be detected through the optical passage.

[0044] Preferably, the perforated disk has two or more such optical windows. These can be arranged on the perforated disk in such a way that, during a complete rotation of the perforated disk, at least a portion of the object is visible without the need for confocal filtering (through the optical openings).

[0045] With each complete rotation of the perforated disk, an object region is imaged through at least one optical passage and through an optical window. The optical window is preferably wide along the circumference of the perforated disk such that the amount of light reaching a light detector through the optical window is greater than or equal to the amount of light reaching the detector through all optical passages combined. This applies to those optical passages located at the same radial distance or with the same radial extent relative to the center of the perforated disk as the optical window. In this case, the optical imaging through the optical window predominates. Confocal filtering through the respective optical passages then occurs with a lower amount of light.

[0046] The at least two optical windows can be located on opposite sides of a center point of the perforated disk, which coincides with an axis of rotation for the disk. The spatial arrangement of the windows can be chosen such that any imbalance of the disk is at least approximately eliminated. Preferably, such an imbalance can be minimized by placing windows of different sizes at radially different distances from the center point.

[0047] To put it simply, a conventional image of the object to be measured can be captured through the optical window. From such an image, the object's position can be determined, for example, thus verifying that during an actual 3D (surface) measurement of the object through at least one optical passage, the object to be measured, or at least the relevant part of the object to be measured, is indeed being measured.

[0048] The described optical window is defined by at least one sufficiently large gap in the optically absorbing material. Depending on the optical transmittance of the substrate material on which the optically absorbing material is applied, the described optical window may also include a correspondingly large through-hole in the substrate.

[0049] Depending on the shape and size of the object (or part thereof) to be captured by the camera, the optical window can have a suitable geometry or size. The following shapes are merely examples: rectangle, slit, circle, ellipse, circular sector, circular annular sector (of the perforated disk).

[0050] The described optical window can be radially offset from the center point of the perforated disk relative to at least one optical passage and / or at least one further optical passage. This allows for the optically separate acquisition of at least a portion of the object to be captured from the acquisition of a 3D surface topography (through the at least one optical passage and / or the at least one further optical passage). Alternatively or in combination, the at least one optical window can also be offset along a circumferential direction relative to the at least one optical passage and / or the at least one further optical passage.

[0051] According to a further embodiment of the invention, the perforated disk has a plurality of recesses and / or optical passages and at least three different circular sectors, wherein (a) in a first circular sector the recesses are arranged with a first spatial distribution, (b) in a second circular sector the recesses are arranged with a second spatial distribution, and (c) in the third circular sector the recesses are arranged with a third spatial distribution. Along a circumferential direction of the perforated disk, the second circular sector is located between the first circular sector and the third circular sector. Furthermore, the first spatial distribution and the third spatial distribution differ from the second spatial distribution. Preferably, the first spatial distribution is the same as the third spatial distribution.Such "sectorization" can advantageously improve the homogeneity of the illumination of a light detector of a (confocal) optical imaging system.

[0052] The aforementioned circular sectors can also be referred to as circular segments.

[0053] In this document, and particularly in this context, the term "spatial distribution" can refer to the positions and / or the number, frequency or density (= number of cutouts and / or optical passages per unit area) of the cutouts.

[0054] It is noted that the perforated disk can also have more than three sectors, the number of sectors being, in particular, a multiple of three. It is further noted that if the perforated disk, as described above, has at least one optical window, this optical window is preferably located in a further circular sector, which is different from the aforementioned (at least three) circular sectors.

[0055] According to a further aspect of the invention, an optical imaging system for detecting the three-dimensional structure of an object to be detected is described. The described optical imaging system comprises (a) a light source for emitting illumination light and (b) a perforated disk according to one of the preceding claims, which perforated disk selects individual light rays of the illumination light through its at least one optical passage and absorbs other light rays of the illumination light through the optically absorbing material. When the object to be detected is located within a spatial detection area of ​​the optical imaging system, the selected light rays strike the surface of the object and are scattered thereon, with at least a portion of the scattered light rays passing through the at least one optical passage as a measuring light.The described optical imaging system further includes (c) a light detector for receiving the measuring light.

[0056] The optical imaging system described here is based on the understanding that the perforated disk described above, due to its extremely strong absorption, can make a significant contribution to reducing the amount or intensity of stray light hitting the light detector to a minimum.

[0057] The term "selecting light rays" in this document means that only those light rays which pass through at least one optical aperture are used to generate measurement signals. This means that unselected light rays are kept away from the light detector and therefore do not contribute to the actual measurement signal.

[0058] According to an embodiment of the invention, the optical imaging system further comprises (a) a first optic which is located in a first optical path between (i) the light source and / or the light receiver and (ii) the perforated disk; and (b) a second optic which is located in a second optical path between (i) the perforated disk and (ii) the spatial detection area of ​​the optical imaging system.

[0059] The first optical system and / or the second optical system, each of which may comprise one or more optical elements such as lenses, mirrors, prisms, etc., may be arranged relative to the perforated disk in such a way and / or have such a focusing effect, particularly through refraction, that the perforated disk is located at a focal point of the light rays of the illumination light and / or the measuring light. Furthermore, the light source and the light detector may be arranged confocally relative to each other. This means that the first optical system (i) sharply focuses a point of light from the light source onto a plane in which at least one opening of the perforated disk is located, and (ii) sharply focuses the (edges of the) opening onto the light receiver.The first optical path and the second optical path each define at least a part of an optical path along which both the illumination light and the measuring light propagate.

[0060] With the optical imaging system defined according to the embodiment described here, a confocal microscope can be realized which, due to the extremely high absorption by the optically absorbing material of the perforated disk, exhibits a high signal-to-noise ratio and thus has high measurement accuracy, especially for determining 3D surface topographies.

[0061] According to a further embodiment of the invention, the optical imaging system further comprises a rotary drive with a stationary component and a rotatable component, wherein the perforated disk is mechanically connected to the rotatable component. The stationary component can also be referred to as the stator and the rotatable component as the rotor of the rotary drive. The rotation is particularly effective about an axis of rotation which is oriented perpendicular to the planar extent of the perforated disk or parallel to a normal vector of the perforated disk.

[0062] By rotating the perforated disk, multiple points on the surface of the object being detected can be sequentially scanned with each individual optical pass. A data processing unit downstream of the light detector can then combine the corresponding measurement signals, each assigned to a specific angular position of an optical pass and its radial distance from the axis of rotation, into an image of the object being detected, representing a 3D surface topography of the object.

[0063] Further advantages and features of the present invention will become apparent from the following exemplary description of currently preferred embodiments. The individual figures in the drawings of this document are to be regarded merely as schematic and not to scale. Brief description of the drawing

[0064] Figure 1shows a confocal optical imaging system with a rotatable perforated disk for measuring the three-dimensional surface of an object, wherein the perforated disk has a substrate and an optically absorbing material with carbon nanotubes applied to it. Figure 2 shows a perforated disk designed as a Nipkov disk with an optical window for capturing a two-dimensional image of an object through the perforated disk. Figure 3 shows a section of a perforated disc in a cross-sectional view. Figure 4 shows a perforated disk with a multitude of optical passages, where the number of optical passages is greater at a larger radial distance from a center of the perforated disk than the number of optical passages at a smaller radial distance. Detailed description

[0065] It should be noted that in the following detailed description, features or components of different embodiments that are identical or at least functionally equivalent to the corresponding features or components of another embodiment are designated with the same reference numerals or with reference numerals whose last two digits are identical to the reference numerals of corresponding identical or at least functionally equivalent features or components. To avoid unnecessary repetition, features or components already explained with reference to a previously described embodiment will not be explained in detail again later.

[0066] Furthermore, it should be noted that the embodiments described below represent only a limited selection of possible embodiments of the invention. In particular, it is possible to combine the features of individual embodiments in a suitable manner, so that a multitude of different embodiments are to be considered obviously disclosed to the person skilled in the art with the embodiments explicitly presented here.

[0067] Furthermore, it should be noted that spatial terms, such as "front" and "back," "top" and "bottom," "left" and "right," etc., are used to describe the relationship of one element to another element or elements, as illustrated in the figures. Accordingly, these spatial terms may apply to orientations that differ from those depicted in the figures. However, it goes without saying that, for the sake of simplicity, all such spatial terms refer to the orientations shown in the drawings and are not necessarily restrictive, since the device, component, etc., depicted, when in use, may assume orientations that differ from those shown in the drawing.

[0068] Figure 1Figure 1 shows a confocal optical imaging system 100 for the three-dimensional measurement of a surface 192 of an object 190. The optical imaging system 100 has a perforated disk 150, which is located at a common first focal point 152 of both (i) an illumination light 112 and (ii) a measuring light 122. More precisely, the common first focal point 152 is defined by the spatial path or focusing of the respective light rays of the illumination light 112 and the measuring light 122. The first focal point 152 is located at the point where the cross-section (of the light rays) of the illumination light 112 and the measuring light 122 is smallest.

[0069] The illumination 112 is generated by a light source 110. According to the embodiment shown here, the illumination 112 is first transformed into a parallel beam of light by an optic 142, for example, a simple lens. This beam of light then passes (in a straight line) through a beam splitter 140 before being focused by a first optic 132 onto the aforementioned first focal point 152. A aperture 162, acting as a pinhole, ensures that only those light rays with significant intensity pass through the aperture 150 which are focused at the first focal point 152. After this first focal point 152, the beam of light from the illumination 112 spreads out again and encounters a second optic 134.The second optic 134, which can also be a simple lens, focuses the illumination light 112 onto a second focal point 154, which is located near the surface 192 to be measured.

[0070] The illumination light 112 incident on object 190 is at least partially scattered at the surface 192 of object 190. Only a comparatively small portion of this scattered light reaches a light detector 120 as measuring light 122. The optical path of this (backscattered) measuring light 122 first passes through (a) the second optic 134, (b) the aperture defined by the opening 162 in the perforated disk 150, and (c) the first optic 132. The measuring light 122, which has been transformed into a parallel beam by the first optic 132, then strikes the beam splitter 140. This beam splitter deflects the parallel measuring light 122 by 90° so that it strikes a reflector 144, which is, for example, an inclined mirror. At the reflector 144, the parallel measuring light 122 is deflected again by 90° and thereby strikes an optic 146, which focuses the measuring light onto a specific measuring point ora specific pixel of the light detector 120 is directed.

[0071] During the measurement, according to the embodiment shown here, the object 190 is moved back and forth along a displacement direction 190a (relative to the optical imaging system 100). Alternatively, the second optic 134 can also be moved or adjusted (relative to the other components of the optical imaging system 100). Furthermore, the entire confocal imaging system 100 can also be moved relative to the object 190. The corresponding displacement movement is illustrated by a double arrow 190a. An (oscillating) displacement of the object 190 around the second focal point 154 results in the beam of the illumination light 112 striking the surface 192 with a different cross-section. Due to the optically confocal arrangement, the intensity of the measurement light 122 backscattered from the surface 192 is determined by the following:More precisely, the intensity of the measuring light 122 striking the light detector 120 is such that this intensity is greatest when the second focal point 154 coincides exactly with a point on the surface 192. If the beam of the measuring light 112 strikes the surface 192 with an enlarged cross-section, the proportion of light backscattered from the surface 192, which passes through the opening or optical passage 172 of the perforated disk 150 and reaches the light detector 120 as measuring light 122, is correspondingly smaller. By evaluating the intensity of the detected measuring light 122 as a function of the distance between the object 190 and the perforated disk 150, the height or distance of the respective measuring point on the surface 192 with respect to the optical imaging system 100 can be determined.By rotating the perforated disc 150 around the axis of rotation 183, various measuring points on the surface 192 can be recorded and thus the three-dimensional height profile of the surface 192 can be measured.

[0072] Even with careful selection and positioning of all optical components involved, it is not possible to completely prevent unwanted stray light from reaching the light detector 120. Particularly disruptive stray light arises when illumination light 112 striking the perforated disk 150 outside the aperture 162 is reflected back and, via the optical components first optic 132, beam splitter 140, reflector 144, and optic 146, reaches the light detector 120.

[0073] The intensity of this scattered light is effectively reduced to a minimum by the fact that in Figure 1The upper surface of the perforated disk 150 is provided with a particularly strongly optically absorbing material 170, which has an absorption coefficient of at least 98%. According to the embodiment shown here, the optically absorbing material 170 is applied to a substrate 160, which consists of a semiconductor material, in particular silicon. The perforated aperture of the perforated disk 150 described above is realized by having a recess 172 in the optically absorbing material 170, which spatially coincides with the aforementioned through-hole 162. The recess 172 and the through-hole 162 thus define an optical path, which constitutes the perforated aperture described above.

[0074] According to the embodiment shown here, the optically absorbing material 170 contains carbon nanotubes, which lead to particularly high optical absorption on the top surface of the perforated disk 150. To further increase this absorption, the carbon nanotubes are aligned (not shown) along a preferred direction, which is oriented parallel to a normal vector of the surface of the perforated disk 150.

[0075] The perforated disk 150, as mentioned above and as is known from conventional confocal optical imaging systems, is rotatable about a rotational axis 183. For this purpose, the perforated disk 150 is connected to a rotary drive 180 via a shaft 182. When the rotary drive is activated, the perforated disk 150 rotates about the rotational axis 183. This causes the optical aperture 162, 172 to "move" in a plane perpendicular to the rotational axis 183, so that, in a known manner, various surface points of the object 190 can be scanned or, more precisely, their distance to the perforated disk 150 can be measured.

[0076] It should be noted that, in deviation from the structural design of the in Figure 1 The following modifications can be made to the confocal optical imaging system 100 shown: (A) The illumination light is not focused but directed as an at least approximately parallel beam of light onto the perforated disk. This means that at a given object distance, the illumination light is not focused on the object's surface but creates a more or less large spot of illumination on the object's surface. (B) The illumination light is coupled into the beam path of the measuring light via the beam splitter. Similarly, the measuring light striking the light detector passes through the beam splitter without deflection (by 90°). In other words, with respect to Figure 1 The light source 110 and light detector 120 are swapped with respect to their spatial arrangement.

[0077] Figure 2Figure 250 shows a perforated disk 250 designed as a so-called Nipkov disk with an optical window 278 for capturing a two-dimensional image of an object through the perforated disk 250. The perforated disk 250 has (in a known manner) a plurality of optical passages 172, each serving as a small aperture and arranged on a spiral around a center point of the perforated disk 250. Figure 2 This center point coincides with shaft 182.

[0078] According to the embodiment shown here, the perforated disk 250 has, in addition to the plurality of optical passages 172, a comparatively large optical window 278. Through this optical window, at least a part of the object in question can be captured by means of a 2D image acquisition. This allows verification, based on a simple image of the object or at least a part of the object, that the object or the part of the object to be captured is located in the correct position, so that the correct surface area of ​​the object is actually measured three-dimensionally in the manner described above.

[0079] Figure 3Figure 1 shows a cross-sectional view of a section of a perforated disk 350 according to a further embodiment of the invention. The perforated disk 350 also comprises a substrate 160 and a layer of a highly optically absorbing material 170 formed on the substrate 160. Suitablely aligned carbon nanotubes in the optically absorbing material 170 ensure particularly high absorption on the top surface of the perforated disk 350. To further prevent the unwanted generation of stray light by scattering at the side walls of the optical passages 162, 172, the optical passages 162, 172 have a conical shape. The cross-section of the optical passages 162, 172 on the side where the optically absorbing material 170 is located is smaller than the cross-section on the opposite side of the perforated disk 350.Alternatively or in combination, the optically absorbing material can also be attached to the side of the substrate where the conical optical passages have the larger cross-section.

[0080] Figure 4 Figure 1 shows a perforated disk 450 with a plurality of optical passages 172 and a plurality of further optical passages 474. According to the embodiment shown here, the further optical passages 474 are spaced further apart from a center point of the perforated disk 450 than the optical passages 172. To prevent the spatial density of optical passages in a radially outer part of the perforated disk 450 from being significantly lower than in a radially inner part of the perforated disk 450, the number of (outer) further optical passages 474 is higher than the number of (inner) optical passages 172. To illustrate this, the following are shown in Figure 1: Figure 4Radial auxiliary lines extending from the center of the perforated disk 450 are drawn, showing that the angular distance between two adjacent (inner) optical passages 172 is twice as large as the angular distance between two adjacent (outer) further optical passages 474. This means that, according to the embodiment shown here, the number of (outer) further optical passages 474 is twice as high as the number of (inner) optical passages 172. Such a "non-star-shaped" spatial distribution of the optical passages 172, 474 allows a larger or at least equal amount of light to be "collected" for larger radial distances during one revolution of the perforated disk 450, relative to the (inner) optical passages 172, without any loss of spatial resolution. This allows the light to be extracted from the Figure 1The light detector shown captures 120 measurement signals with a large signal-to-noise ratio that is at least approximately the same in the field of view of the confocal image.

[0081] Alternatively to, or in combination with, such a distribution of the number of optical passages dependent on the radial distance to the center of the perforated disk, the size or diameter of the optical passages can also vary spatially and, in particular, depend on the radial distance to the center of the perforated disk. For example, the diameters of the optical passages for outer passages can be larger than those for inner passages.

[0082] It is noted that the term "have" does not exclude other elements and that "a" does not exclude a plurality. Elements described in connection with different embodiments may also be combined. It should also be noted that reference numerals in the claims should not be interpreted as limiting the scope of protection of the claims. Reference symbol:

[0083] 100 Confocal optical imaging system 110 Light source 112 Illumination light 120 Light detector 122 Measuring light 132 First optics 134 Second optics 140 Beam splitter 142 Optics 146 Optics 150 Perforated disc 152 First focal point 154 Second focal point 160 Substrate 162 Pass-through aperture / optical passage 170 Optically absorbing material 172 Recess / optical passage 180 Rotary drive 182 Shaft 183 Axis of rotation 190 Object (to be detected) 190a Translation movement 192 Surface 250 Perforated disc 278 Optical window 350 Perforated disc 450 Perforated disc 474 Further recess / further optical passage

Claims

1. A perforated disk (150, 250, 350, 450) for selecting light for an optical imaging in a confocal imaging system (100), the perforated disk having an optically absorbing material (170) which has an absorption coefficient of at least 98%, wherein at least one opening (172) is present in the optically absorbing material (170) and defines an optical passage (172) through the perforated disk; and a substrate (160), wherein the optically absorbing material (170) is a coating on the substrate (160), and wherein the substrate (160) has a passage opening (162) in the region of the at least one opening (172).

2. A perforated disk according to claim 1, wherein the substrate (160) is an optically transparent substrate (160).

3. A perforated disk according to claim 1 or 2, wherein the substrate (160) has a semiconductor material, wherein in particular the semiconductor material is silicon.

4. A perforated disk according to any one of the preceding claims, wherein the passage opening (160) has an opening cross-section, which changes continuously or discretely along a direction parallel to a normal vector of the perforated disk, wherein in particular the passage opening (162) has the shape of a truncated cone.

5. A perforated disk according to the preceding claim, wherein at least one sidewall of the passage opening (162) is inclined so strongly with respect to the surface of the perforated disk that no undesired blockings (vignettings), reflections or scatterings of light beams (122), which pass through the corresponding opening (172) of the perforated disk, occur at this sidewall.

6. A perforated disk according to any one of the preceding claims, wherein the at least one opening (172) has a width between 1 µm and 30 µm, and in particular a width between 2 µm and 10 µm, and / or wherein the absorption coefficient is greater than 99%, in particular greater than 99.5%, and further in particular greater than 99.95%.

7. A perforated disk according to any one of the preceding claims, wherein the optically absorbing material has carbon nanotubes, wherein in particular the carbon nanotubes are oriented along a preferred direction, wherein the preferred direction is in particular aligned parallel to a normal vector of the perforated disk.

8. A perforated disk according to any one of the preceding claims, further having at least one further opening (474), wherein the further opening (474) defines a further optical passage (474) which is greater than the optical passage (172).

9. A perforated disk according to any one of the preceding claims, wherein a plurality of optical passages (172, 474) are present, which have different radial distances with respect to a center point of the perforated disk, wherein (a) for a first radial distance, two neighboring first optical passages (172) have a first angular distance with respect to the center point, and (b) for a second radial distance, two neighboring second optical passages (474) have a second angular distance with respect to the center point, wherein if the first distance is greater than the second distance, the first angular distance is smaller than the second angular distance.

10. A perforated disk according to any one of the preceding claims, wherein the optical passages (172, 474) are arranged spatially distributed over the perforated disk such that an at least approximately equal signal-to-noise ratio is achievable across a predefined field of view of the confocal optical imaging.

11. A perforated disk according to any one of the preceding claims, further having at least one optical window (278), which is so large that at least a part region of an object (190) to be captured can be imaged through the optical window (278) onto a camera (120), wherein the imageable part region of the object (190) is larger than a region of the object (190), which region can be captured through the optical passage (172).

12. A perforated disk according to any one of the preceding claims, wherein the perforated disk has a plurality of openings (172) and at least three different sectors of a circle, wherein, in a first sector, the openings (172) are arranged with a first spatial distribution, in a second sector, the openings (172) are arranged with a second spatial distribution, and, in the third sector, the openings (172) are arranged with a third spatial distribution, wherein, along a circumferential direction of the perforated disk, the second sector is located between the first sector and the third sector, and the first spatial distribution and the third spatial distribution are different from the second spatial distribution and in particular the first spatial distribution is identical to the third spatial distribution.

13. An optical imaging system (100) for capturing the three-dimensional structure of an object (190), the optical imaging system (100) having a light source (110) for emitting an illumination light (112); a perforated disk (150, 250, 350, 450) according to any one of the preceding claims, which perforated disk (150, 250, 350, 450) selects individual light beams of the illumination light (112) through its at least one optical passage (172) and absorbs other light beams of the illumination light (112) by means of the optically absorbing material (170), wherein, if the object (190) to be captured is located in a spatial capturing region of the optical imaging system (100), the selected light beams impinge on the surface (192) of the object (190) and are scattered at said surface, wherein at least some of the scattered light beams pass through the at least one optical passage (172) as a measurement light (122); and a light detector (120) for receiving the measurement light (122).

14. An optical imaging system (100) according to the preceding claim, further having a first optics (132) which is located in a first optical path between (i) the light source (110) and / or the light receiver (120) and (ii) the perforated disk (150, 250, 350, 450); and a second optics (134) which is located in a second optical path between (i) the perforated disk (150, 250, 350, 450) and (ii) the spatial capturing region of the optical imaging system (100), and / or further having a rotary drive (180) having a stationary component and a rotatable component, wherein the perforated disk (150, 250, 350, 450) is mechanically tied to the rotatable component.