Method, optical device and retrofit kit for generating an optical sheet using a retroreflector

Abstract

The present invention relates to an optical device (100) and method for generating a light sheet (102), and a retrofit kit for a light sheet microscope for generating a light sheet. The optical device includes an optical subsystem (104) having a plurality of collimated light beams (108) at an output side (106) of the optical subsystem, the plurality of collimated light beams reaching a common point (110). A retroreflector (112) is also provided, having a beam input side (114) where the light beams enter the retroreflector and a beam output side (116) where the light beams exit the retroreflector. The path length (118) traveled by the light beams within the retroreflector between the beam input side and the beam output side depends on the angle of incidence (120) of each light beam at the beam input side. Finally, the optical device includes a light sheet optic (122), in which the light beams emitted from the beam output side of the retroreflector extend into the light sheet optic, and differently directed light sheets are formed from each light beam at the output side of the light sheet optic (124). This device allows for the rapid generation of multiple different light sheets without the use of fragile mechanisms.

Description

Technical Field

[0001] The present invention relates to a method and an optical device for generating an optical sheet, such as used in, for example, light sheet microscopy.

Background Art

[0002] An optical sheet can be generated by focusing a light beam, particularly a laser beam, in only one spatial direction. By this kind of focusing, sheet-like light that illuminates only one thin layer of a sample is generated. The thickness of the optical sheet is typically between about several hundred nanometers and several micrometers.

[0003] To scan a sample or to avoid shading, a plurality of optical sheets that are respectively directed differently are generated. For this purpose, a mechanism having a movable element, for example, a movable mirror, is usually used. Such a mechanism is expensive, time-consuming to adjust, and prone to failure.

Summary of the Invention

Problems to be Solved by the Invention

[0004] Therefore, it is desirable to provide an apparatus and a method that can easily generate an optical sheet and are wear-resistant.

Means for Solving the Problems

[0005] According to one aspect of the present invention, this is an optical device for generating an optical sheet, the optical device having an optical subsystem, the optical subsystem having a plurality of collimated light beams on the output side of the optical subsystem, the plurality of collimated light beams reaching a single common point, the optical device having a retroreflector, the retroreflector having a beam input side where a light beam is incident on the retroreflector and a beam output side where the light beam exits the retroreflector, the path length traveled by the light beam between the beam input side and the beam output side within the retroreflector depending on the angle of incidence of each light beam at the beam input side, the optical device having an optical sheet optical system, the light beam emitted from the beam output side of the retroreflector extending into the optical sheet optical system, and at the output side of the optical sheet optical system, an optical sheet is shaped such that each light beam is directed differently from each other, which is made possible by the optical device.

[0006] According to a further aspect of the present invention, there is provided a retrofit kit for a light sheet microscope, the retrofit kit having an optical subsystem, the optical subsystem having a plurality of collimated light beams on the output side of the optical subsystem, the plurality of collimated light beams reaching a single common point, the retrofit kit having a retroreflector, the retroreflector having a beam input side where a light beam is incident on the retroreflector and a beam output side where the light beam exits the retroreflector, the path length traveled by the light beam between the beam input side and the beam output side within the retroreflector depending on the angle of incidence of each light beam at the beam input side, and the retrofit kit being configured to be disposed in the illumination beam path of the light sheet microscope.

[0007] Finally, a method for generating a light sheet, preferably using the optical device presented above, is contemplated, in which a plurality of collimated light pulses reaching a common point are incident on a retroreflector and, within the retroreflector, follow a path length that depends on the angle of incidence within the retroreflector and then exit the retroreflector and are each transformed into one light sheet.

[0008] By using such an optical device, such a retrofit kit, and such a method, it becomes possible to create a plurality of light sheets without using a mechanism that is prone to wear.

[0009] In this case, it is advantageous for the light beam to be collimated within the retroreflector, whereby the light sheet can be sharply focused even when the path length is large. Thanks to the collimation of the plurality of light beams arriving at one point, generally, a normal light sheet optical system for generating a light sheet can be used. The path length that depends on the angle of incidence enables, in particular, the use of a pulsed light source. This is because the different path lengths lead to a propagation time difference and thus result in a plurality of light sheets generated at different times. This can be utilized to generate an incoherent light sheet from a light beam that is still coherent in front of the retroreflector or to generate a plurality of light sheets that are stepped, for example, in the depth direction, both temporally and spatially. As a result, an apparatus is obtained that can instantaneously generate a plurality of light sheets individually on the optical path and thus without wear.

[0010] The light beam in the above-mentioned sense, in the sense of beam optics, represents the beam path of an optical device or a retrofit kit, or represents the optical axis along which a (collimated) beam bundle travels. At this time, the photon beam or electromagnetic wave traveling along the light beam may not specifically exist. Even when the optical device is not in operation, the beam path and the light beam exist. Since light travels along the light beam, in the following, the expression "light beam" is used for both the beam path and the light traveling along the beam path.

[0011] The present invention can be further improved by the following features, which are each advantageous alone, independent of each other, and can be arbitrarily combined with each other. In this case, each feature can be uniformly used for both the optical device, the retrofit kit, and the method.

[0012] According to a first advantageous embodiment, a plurality of light beams, especially all light beams, can each have a different path length in the retroreflector.

[0013] Furthermore, it is advantageous if each light beam has a different angle of incidence, at which the light beam is incident on the retroreflector. The angle of incidence in this case is the angle between the light beam and the perpendicular to the mirror plane of the retroreflector where the light beam impinges.

[0014] In order to ensure that each light beam follows a different path length in the retroreflector when a plurality of light beams reach one point, the path length of the light beam in the retroreflector can be made a strictly monotonic function of the angle of incidence. Therefore, the smaller the angle of incidence, the shorter the path length can be.

[0015] By means of these three measures, each light beam will enter the light sheet optical system at a different time point independently of each other and based on different wavelengths. As a result, they can be distinguished from each other in terms of their respective postures and orientations with respect to the optical axis and also in terms of phase posture. Thus, it becomes possible to aim and use them to generate a specific light sheet.

[0016] In a further advantageous embodiment, the light beams on the beam output side can extend relative to each other at the same angle as the light beams on the beam input side. This includes two possibilities: the possibility that the light beams on the beam output side converge towards a common point and the possibility that these light beams travel away from each other in a direction away from a common point. Both have the advantage that the relative extension of the light beams with respect to each other is not impaired by the retroreflector. In particular, the part of the light beam that is directed from the beam output side towards the light sheet optical system can be emitted from a common point.

[0017] In one embodiment, an optical device or an aftermarket set is used to generate light sheets that are superimposed on each other so that shading by the sample is reduced or even eliminated. For this purpose, it is advantageous if the light sheets generated from a plurality of different light beams have different propagation directions. Alternatively or in addition, the light sheets may be in the same plane.

[0018] Each light beam, preferably all light beams, can be at least partially located in one plane between the optical subsystem and the light sheet optical system, i.e., can extend in the same plane as each other. In particular, the light beams are adjacent to each other in a direction or plane parallel to the spatial direction in which the light beam is focused by the cylindrical lens of the light sheet optical system, for example, immediately before the light sheet optical system (i.e., on the light source side). In this way, in cooperation with the objective lens of the light sheet optical system, a plurality of light sheets on the same plane with different orientations are generated.

[0019] In order to prevent the foci of the plurality of light sheets from being located at different intervals with respect to the objective lens, the light beam should also be collimated on the beam output side.

[0020] When the beam input side and the beam output side coincide, that is, when the light beam also exits from the retroreflector at the location where the light beam enters the retroreflector, a compact structural form can be realized. In the case of such a structural form, a beam splitter can be provided between the beam output side and the light sheet optical system. The light beam emitted from the retroreflector is preferably deflected to the light sheet optical system by the beam splitter. The light beam directed toward the beam input side can extend through the beam splitter.

[0021] According to a further advantageous embodiment, the common point can coincide with the beam input side. This makes it possible to keep the dimensions of the beam input side small. The common point can be located, in particular, on the mirror surface of the retroreflector. The common point is preferably located on the optical axis that coincides with the optical axis of the optical subsystem, preferably the light sheet optical system.

[0022] For a compact structural form of the optical device or the retrofit kit, it is advantageous that, in at least some of the plurality of light beams, the portion of the light beam incident on the retroreflector that ends on the beam input side and the portion of the same light beam exiting from the retroreflector that starts on the beam output side are congruent.

[0023] According to a particularly simple and compact structural form, the retroreflector can have two flat mirrors and / or two mirrors tilted relative to each other around only one spatial direction. The light beam can have an inversion point within the retroreflector where the propagation direction of the light beam is reversed. In this embodiment, the light beam is first reflected within the retroreflector in a direction away from the beam input side until the inversion point, and then is reflected back from the inversion point towards the beam input side again. In this case, the mirrors can be spaced apart from each other at any location. These mirrors are preferably spaced apart from each other at a slightly smaller distance at the inversion point than at the beam input side and / or the beam output side. To keep the structural dimensions small, the beam input side and the beam output side can be arranged at the same end of the retroreflector. The inversion point is spaced apart from the beam input side and the beam output side in the direction of the other end. In this case, the distance from the beam input side and / or the beam output side to the inversion point can depend on the incident angle of the light beam.

[0024] To generate the largest possible path length or path length difference within the retroreflector, the angle at which the mirrors are tilted relative to each other is preferably smaller than the angle between the light beams located farthest apart. For example, the angle at which the mirrors are tilted relative to each other can be less than 10 -2 rad and / or greater than 10 -4 rad. In other embodiments, the angle at which the mirrors are tilted relative to each other is less than 10 degrees or less than 5 degrees. The angle at which the mirrors are tilted relative to each other determines the path length difference between the light beams within the retroreflector. The path length difference, and thus the angle at which the mirrors are tilted relative to each other, is generally set depending on the coherence length of the light from the light source.

[0025] According to a further embodiment, the incident angles of at least some, preferably all, of the light beams may be different integer multiples of the angle by which the mirrors are tilted relative to each other. In such an embodiment, the light beam incident on the retroreflector on the beam input side and the light beam exiting the retroreflector on the beam output side extend congruently.

[0026] The optical device or retrofit kit can have an adjustment device, in particular a motor-driven adjustment device, configured to adjust the angle between the mirrors. An electronic control unit can be provided to control the adjustment device. The adjustment device can have a drive element, such as a motor or other actuator, acting on at least one mirror. The adjustment device enables the relative attitude and / or orientation of the light beam incident on the light sheet optical system and / or the path length and / or path length difference within the retroreflector to be adapted to the respective requirements. For example, the angle by which two mirrors of the retroreflector are tilted relative to each other can be automatically varied using the adjustment device depending on the coherence length of the light of the light beam, i.e., the coherence length of the spectrum of the light of the light beam and / or the number, orientation and / or attitude of the light sheets to be generated.

[0027] Between the two mirror planes, the retroreflector can have a volume filled with a gaseous medium or a vacuum, and this volume can be sealed against the outside. Alternatively, the light beam can also extend through glass within the retroreflector. For example, the retroreflector can be manufactured from glass, in particular from a glass block, for example in a monolithic structural form. Mirrors can be deposited on two opposing surfaces of the glass block or the two opposing surfaces of the glass block can be mirror-finished.

[0028] The common point at which the plurality of light beams arrive is preferably located within the (light source side) rear focal plane of the cylindrical lens of the light sheet optical system, or within a plane optically conjugate to the rear focal plane. The cylindrical lens can be located at the end of the light sheet optical system facing the retroreflector, i.e., on the input side of the light sheet optical system. The cylindrical lens can be located, in particular, between the retroreflector and the microscope objective lens.

[0029] An optical device and a retrofit kit can be used to generate a light sheet from light beams that were originally coherent with each other and to superimpose them on the same plane without interference. Such a superimposition can be used, for example, to avoid shading. This can be achieved, in one advantageous embodiment, by making the shortest difference between the path lengths of the plurality of different light beams greater than the coherence length of the light of the light beams. To avoid shading, the light sheets are preferably in the same plane.

[0030] The light source can be part of the optical device.

[0031] Furthermore, it is advantageous if the light source is configured to generate optical pulses or if the light source is a pulsed light source. In this embodiment, the optical device, in particular the retroreflector, is configured to generate temporally sequential optical pulses along the light beam at the beam output side based on different path lengths within the retroreflector from the optical pulses that were originally synchronized along the light beam at the beam input side. The time interval between the sequentially consecutive optical pulses results from the path length difference within the retroreflector. The light sheet optical system is configured to generate a pulsed light sheet that is temporally sequential from the temporally sequential optical pulses propagating along the light beam. The optical pulses along the respective different light beams are temporally offset from each other at the beam output side of the retroreflector. In this way, a light sheet is generated from the optical pulses that sequentially arrive at the light sheet optical system. By such means, it becomes possible to scan a sample using a plurality of sequentially consecutive light sheets without requiring a mechanism that is prone to failure.

[0032] The light source is preferably a laser, such as a gas laser or a diode laser.

[0033] The optical subsystem can be configured to split one input beam, for example one laser beam, into a plurality of light beams. For example, the optical subsystem can have one or more beam splitters, in particular a linear lens assembly, in particular a microlens assembly and / or a grating or a semi-transparent mirror, and these can also be arranged in a cascade connection. The lenses of the lens assembly can be cylindrical lenses. If the light sheet optical system has a cylindrical lens, it is not necessary to use a cylindrical lens in the optical subsystem.

[0034] On the output side of the optical subsystem, the plurality of light beams are preferably positioned adjacent to each other in one plane.

[0035] The optical subsystem can have a lens or a lens system on the output side of the optical subsystem, through which the light beam passes, and this lens or lens system ensures the collimation of the light beam and deflects the individual light beams towards the optical axis according to their respective intervals so that they extend through a common point on the optical axis.

[0036] To generate a collimated light beam, the optical subsystem can have a collimating device.

[0037] The optical device in one of the above-described embodiments can be arranged as part of a microscope, particularly in the illumination beam path. The microscope can have a detector optical system, and the optical axis of this detector optical system is preferably oriented perpendicular to the plane of the light sheet generated by the light sheet optical system.

[0038] In a further embodiment, the microscope can have a light source configured to generate light having a predetermined coherence length, and the light beam is generated from the light of this light source.

[0039] Hereinafter, the present invention will be exemplarily described with reference to the drawings based on one embodiment. In this specification and the drawings, the same reference numerals are used for features corresponding to each other with respect to structure and / or function.

[0040] According to the above-described embodiments, the individual features realized in the exemplary embodiments can be omitted if their technical effects are not important in a specific application. Conversely, the features from the above description can be added to the exemplary embodiments if the technical effects associated with these features are important in a specific application.

Brief Description of the Drawings

[0041]

Figure 1

Figure 2

Figure 3

Figure 4

Mode for Carrying Out the Invention

[0042] Based on FIGS. 1 to 3, the structure and function of the optical device 100 will be described below.

[0043] The optical device 100 is used to generate a plurality of optical sheets 102. Preferably, the optical device 100 is used to generate a plurality of incoherent optical sheets 102 on the same plane having different propagation directions 126 from the light beam 108, particularly from the optical pulses 158, 158a, 158b. In this case, one optical sheet 102 is generated from each light beam 108. Alternatively, the optical device 100 can be used to generate a plurality of mutually separated parallel optical sheets 102 from a plurality of light beams 108.

[0044] The optical device 100 has an optical subsystem 104, and this optical subsystem 104 has a plurality of collimated light beams 108 on the output side 106 of the optical subsystem 104, and these plurality of collimated light beams 108 reach one common point 110. In this case, the light beam 108 represents the optical axis along which the collimated beam bundle travels. The light beam is located on the output side of the optical subsystem, and on this output side, a plurality of light beams are emitted from the optical subsystem in the direction of the retroreflector 112, preferably adjacent to each other in one plane.

[0045] The optical subsystem 104 can have a lens 107 at the output side 106 of the optical subsystem 104, and this lens 107 ensures that the light beam 108 emitted from the optical subsystem 104 to the retroreflector 112 is collimated and reaches the point 110.

[0046] The optical device 100 further has a retroreflector 112. At the beam input side 114 of the retroreflector 112, the light beam 108 is incident on the retroreflector 112. The light beam 108 exits the retroreflector 112 again at the beam output side 116. Inside the retroreflector, the light beam follows a path length 118 between the beam input side 114 and the beam output side 116, and this path length 118 depends on the incident angle 120 of each light beam at the beam input side 114.

[0047] FIG. 1 illustratively shows two light beams. However, the number of light beams 108 can be any number and depends, for example, on the then-current use purpose of the optical device 100 and the number of light sheets 102 required. The path length 118 is illustrated as extending to the right from the retroreflector 112 in FIG. 1 to enable easier comparison of these path lengths. In reality, the path length 118 is determined by the zigzag beam path of each light beam 108 inside the retroreflector 112.

[0048] The optical device 100 further has a light sheet optical system 122, and the light beam 108 extends from the beam output side 116 of the retroreflector 112 into this light sheet optical system 122. The light sheet optical system 122 generates light sheets 102 that are respectively directed differently from the light beam 108 at the output side 124 of the light sheet optical system 122.

[0049] The optical device 100 can be part of a light sheet microscope 180, for example, can form the illumination beam path 182 of the light sheet microscope 180 or can be arranged in the illumination beam path.

[0050] The optical device 100 can also be configured as a retrofit kit for a light sheet microscope 180 in which the optical device 100 has not yet been provided. The retrofit kit has the optical device 100 or further components of the optical device 100 to be assembled and is configured to be arranged in the illumination beam path 182 of the light sheet microscope.

[0051] The light sheet microscope 180 can be provided with a detector optical system 184, and the optical axis 186 of this detector optical system 184 is oriented perpendicular to the optical axis 188 of the light sheet optical system 122.

[0052] The optical device 100 can have a light source 152. The light source 152 can be a pulsed light source that generates light pulses 158. For example, the light source can be a laser such as a gas laser or a diode laser.

[0053] The light source 152 preferably generates light having a coherence length 154 that depends on the structural form and / or operating form of the light source.

[0054] In the illustrated variant, the optical subsystem 104 is configured to generate a plurality of light beams 108 from the input light beam 170. For this purpose, an optical device 160 for splitting the light beam, for example, a particularly linear lens assembly 162 such as a microlens assembly and / or an assembly of beam splitters such as a grating or a semi-transparent mirror can be provided. The beam splitters can also be arranged in cascade connection. In FIG. 1, a microlens assembly is shown merely as an example. The lens 163 of the lens assembly 162 can be a cylindrical lens. In this case, the light beam is focused in the plane of the figure and collimated perpendicular to the plane of the figure.

[0055] When the lens 163 of the lens assembly 162 is a cylindrical lens, using only the lens 107 would cause a plurality of beams collimated perpendicular to the drawing plane to converge (approximately at point 110), which is not desirable. Therefore, in this case, advantageously, an additional (cylindrical) lens or (cylindrical) lens assembly can be further provided on the light source side of the lens 107. The additional (cylindrical) lens or (cylindrical) lens assembly focuses in a direction perpendicular to the drawing plane onto the (light source side) rear focal plane of the lens 107, provided that it focuses more strongly than the lens assembly 162 or the lens 163 of the lens assembly in the drawing plane so as to form an optical sheet within the sample.

[0056] When an optical pulse 158 is generated along the input optical beam 170 from the light source 152, this optical pulse 158 is split by the optical device 160 into a plurality of different optical pulses 158a, 158b, which may be synchronized with each other, among other things, and can propagate along different optical beams 108 respectively.

[0057] As can be seen from FIGS. 1 and 3, these individual optical beams 108 are at least partially, preferably throughout the entire illumination beam path 182, but before entering at least the light sheet optical system 122, located adjacent to each other within a plane 300 that is perpendicular to the drawing plane in FIG. 3 and is shown by a dashed line. In particular, the optical beams 108 are also located within one plane, preferably within plane 300, or within one plane rotated with respect to plane 300, also between the beam output side 116 of the retroreflector 112 and the light sheet optical system 122.

[0058] The light sheet optical system 122 has a rear focal plane 150 or a plane optically conjugate to the rear focal plane 150, and within these planes, the point 110 where the collimated optical beam 108 generated by the optical subsystem 104 arrives is located.

[0059] The light sheet optical system 122 can have a cylindrical lens 164. The point 110 can be located, in particular, within the rear focal plane 150 of this cylindrical lens 164 or within a plane optically conjugate to the rear focal plane 150.

[0060] Furthermore, the light sheet optical system 122 can have an objective lens 166, which can also be referred to as a microscope objective lens. Within the pupil 200 (FIG. 2) of the objective lens 166, a plurality of light beams 108 are positioned adjacent to each other. The light propagating along the light beam 108 has an elliptical cross-section 202 with respect to each light beam 108 within the pupil 200.

[0061] The light sheets 102 generated by the light sheet optical system intersect each other. Preferably, the light sheets 102 are arranged in the same plane as each other and have different propagation directions 126. That is, the propagation directions 126 of these light sheets 102 are located within one common plane. Then, these light sheets preferably intersect each other within the sample volume 168, and this sample volume 168 can be located, in particular, on the optical axis 186 of the detector optical system 184. This applies, for example, when the plane 300 extends parallel to the plane 190 focused by the cylindrical lens 164. In FIG. 1, this is the plane of the drawing.

[0062] The cylindrical lens 164 generates an elliptical focus as shown in FIG. 2. The elliptical cross-section of the focus rotates by 90 degrees when passing through the objective lens 166. In that case, the light sheets overlap vertically and are more strongly focused, that is, thinner, along the direction of the major axis of the ellipse. This can also be explained as a plurality of light sheets having an elliptical cross-section being positioned parallel to each other at the rear focal plane of the objective lens, that is, on the light source side. The ellipse is rotated by 90 degrees after passing through the objective lens 166, and in that case, they overlap vertically at the focal plane of the objective lens.

[0063] A plurality of light sheets 102 on the same plane that can rotate relative to each other avoid strip-shaped artifacts generated by shading and refraction of the light sheet due to an object within the sample volume 168. The sample volume 168 is illuminated from different angles but on the same plane by the plurality of light sheets 102, thereby minimizing shading.

[0064] It should be noted that when the light sheets 102 overlap vertically, the individual light sheets 102 are incoherent with each other to avoid interference. This can be easily achieved by making the minimum path length difference 156 between all the light beams 108 used to generate the light sheets 102 greater than the coherence length 154 of the light of the light beams 108.

[0065] When the light source 152 generates a temporal sequence of input light pulses 158 having, for example, a coherence length 154, the individual light pulses 158a, 158b used to generate the light sheets 102, which are formed by splitting the input light pulse 158 by the optical subsystem 104, should be temporally separated from each other by at least one coherence length 154.

[0066] That is, the retroreflector 112 is used to generate light beams 108 that are incoherent with each other on the beam output side 116 from light beams 108 that are coherent with each other on the beam input side 114.

[0067] This is achieved by the fact that the plurality of light beams 108 are incident on the retroreflector 112 at different incident angles 120, and the path length 118 within the retroreflector 112 depends on those incident angles 120. Therefore, the retroreflector 112 converts the difference in the incident angles 120 into a path length difference 156. When all the path length differences 156 between the light beams 108 within the retroreflector 112 are greater than the coherence length 154, the light propagating along the light beams 108 becomes incoherent.

[0068] Basically, the retroreflector 112 can have any structural form, for example, it can have a structural form as a triple mirror or a triplet prism, as a cat's eye, or as a Luneburg lens. However, it is preferable that the retroreflector is configured such that a large path length difference 156 is generated between adjacent light beams even if the incident angles of the adjacent light beams change slightly. Further, it is preferable that the angular ratio existing between the individual collimated light beams at the beam input side 114 is also maintained at the beam output side 116. That is, the retroreflector 112 should not change the relative positions and orientations of the individual light beams 108 with respect to each other. Finally, it would be advantageous if the beam input side 114 is not far from the beam output side 116 of the retroreflector 112 so as to maintain a compact structural form.

[0069] The retroreflector 112 illustratively shown in FIG. 1 meets these requirements.

[0070] The retroreflector 112 has two flat mirrors 138, 140 in the illustrated embodiment, and these two flat mirrors 138, 140 are inclined with respect to their respective parallel postures, preferably by an angle 144 of 10 -4 ~10 -2 rad. Angles less than 10 degrees or less than 5° are also possible. The central axis when the two mirrors 138, 140 are inclined with respect to each other is positioned perpendicular to the plane 300 and extends parallel to the mirror plane. The volume 192 between the two mirrors can be filled with a gas or air and can be sealed against the outside. Alternatively, the retroreflector 112 can also be manufactured from a glass block, whereby the light beam 108 extends through the glass within the retroreflector 112. In this case, the mirrors 138, 140 are formed by two opposing inclined planes of the glass block.

[0071] The beam input side 114 is located on the surface 132 of the mirror 138 in the illustrated embodiment. The central plane 148, which is equidistant from the opposing mirrors 138, 140 between the two mirrors 138, 140, is perpendicular to the plane 300 and extends obliquely to the illumination beam path 182.

[0072] The point 110 at which the collimated light beam 108 sequentially arrives can be located in front of or within the retroreflector 112. In the embodiment shown in FIG. 1, this point 110 is located on the mirror surface 132, that is, on the beam input side 114. The beam output side is also located at this location.

[0073] FIG. 1 schematically shows the beam paths of the two light beams 108 within the retroreflector 112.

[0074] The light beam 108 is reciprocally reflected between the two mirrors 138, 140. Since the distance between the two mirrors decreases in the direction away from the beam input side, the light beam 108 is reflected in the direction away from the beam input side into the retroreflector 112. In this case, the incident angle decreases each time it is reflected at one of the mirrors 138, 140 based on the angle 144. That is, as the number of reflections of the light beam 108 increases, it collides with the mirrors 138, 140 more and more steeply, and then at the inversion point 142, the direction of the light beam 108 within the retroreflector 112 is inverted, and the light beam 108 is reflected back towards the beam input side 114 again.

[0075] On the path from the inversion point 142 to the beam input side 114, the incident angle with respect to the mirrors 138, 140 increases again each time it is reflected at one of the mirrors 138, 140. The retroreflected light beam 108 exits the retroreflector 112 again at the beam input side 114. Therefore, in the embodiment shown in FIG. 1, the beam input side 114 and the beam output side 116 spatially coincide.

[0076] When considering the zigzag reflection of the light beam 108 within this retroreflector 112 as a spatial wave, the frequency of this spatial wave increases up to the inflection point and then decreases again. Based on the fact that the angle 144 is very small, a large number of reflections occur, whereby the path length difference 156 can be adapted to the coherence length 154 by adjusting the angle 144.

[0077] When the incident angle of the light beam 108 at the beam input side 114 is an integer multiple of the angle 144, the light beam 108 is reflected congruently and returned within the retroreflector 112. Therefore, in one embodiment of the optical device 100, all the incident angles 120 of the light beam are integer multiples of the angle 144. Thereby, the light beams 134, 108 incident on the retroreflector 112 become congruent with the retroreflected light beams 136, 108.

[0078] The beam splitter 130 in the illumination beam path 182 reflects the light beams 108, 136 arriving from the beam output side 116 to the light sheet optical system 122, while the light beams 108, 134 propagating in the direction of the beam input side 114 pass through the beam splitter 130.

[0079] The light beams 108 incident on the light sheet optical system 122 are already temporally offset from each other or are decoherent as described above based on the fact that the lengths of the reflection paths within the retroreflector 112 are different from each other.

[0080] According to FIG. 4, to generate a light sheet, in a first step 400, a plurality of collimated light pulses 158a, 158b that reach a common point 110 are incident on the retroreflector 112. In step 402, these light pulses follow path lengths 118 that depend on their respective incident angles 120 within the retroreflector 112.

[0081] Subsequently, the optical pulse exits from the retroreflector 112 in step 404 and is transformed into one optical sheet 102 each. In step 406, a plurality of optical sheets 102 can be generated on the same plane so as to have different propagation directions intersecting each other within the sample volume 168.

[0082] The optical device 100 can have an adjustment device 194 configured to change the angle 144 or to tilt at least one of the mirrors 138, 140. The adjustment device 194 can have a drive element 196, such as a motor or an actuator, acting on at least one of the mirrors 138, 140, and a control device 198 for controlling the drive element 196. By adjusting the angle 144, for example, the number of optical sheets 102 or the path length difference 156 can be adapted.

[0083] As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items and may be abbreviated as " / ".

[0084] Although several aspects have been described in the context of an apparatus, it is clear that these aspects also represent a description of the corresponding method, where a block or apparatus corresponds to a step or a feature of a step. Similarly, aspects described in the context of a step also represent a description of the corresponding block or item or feature of the corresponding apparatus.

Explanation of Reference Numerals

[0085] 100 Optical device 102 Optical sheet 104 Optical subsystem 106 Output side of the optical subsystem 107 Lens on the output side of the optical subsystem 108 Light beam 110 Common point where the light beam arrives 112 Retroreflector 114 Beam input side of the retroreflector 116 Beam output side of the retroreflector 118 Optical path length of the light beam in the retroreflector 120 Incident angle of the light beam on the retroreflector 122 Light sheet optical system 124 Output side of the light sheet optical system 126 Propagation direction of the light sheet 130 Beam splitter 132 Mirror surface 134 Section of the light beam 136 Section of the light beam 138 Mirror 140 Mirror 142 Inversion point 144 Angle at which the mirrors are inclined to each other 146 Time offset 148 Central plane 150 Rear focal plane of the light sheet objective lens or the light sheet optical system 152 Light source 154 Coherence length 156 Path length difference 158 Input optical pulse 158a, 158b Optical pulses generated from the input optical pulse 160 Optical device for splitting the light beam 162 Lens assembly 163 Cylindrical lens of the lens assembly 164 Cylindrical lens 166 Objective lens 168 Sample volume 170 Input light beam 180 Light sheet microscope 182 Illumination beam path 184 Detector optical system 186 Optical axis of the detector optical system 188 Optical axis of the light sheet optical system 190 Plane focused by the cylindrical lens 192 Volume between the mirrors 194 Adjustment device 196 drive element 198 control device 200 pupil 202 elliptical cross-section 300 plane of the light beam 400 light beam incidence 401 reflection of the light beam depending on the incident angle 404 generate a light sheet 406 form a plurality of light sheets on the same plane intersecting each other

Claims

1. An optical device (100) for generating an optical sheet (102), wherein the optical device (100) has an optical subsystem (104), the optical subsystem (104) has a plurality of collimated light beams (108) at an output side (106) of the optical subsystem (104), and the plurality of collimated light beams (108) reach one common point (110), the optical device (100) has a retroreflector (112), the retroreflector (112) has a beam input side (114) where the light beam (108) is incident on the retroreflector (112) and a beam output side (116) where the light beam (108) exits from the retroreflector (112), a path length (118) traveled by the light beam (108) between the beam input side (114) and the beam output side (116) within the retroreflector (112) depends on an incident angle (120) of each of the light beams at the beam input side (114), the optical device (100) has an optical sheet optical system (122), the light beam (108) emitted from the beam output side (116) of the retroreflector (112) extends into the optical sheet optical system (122), and at an output side (124) of the optical sheet optical system (122), an optical sheet (102) is formed which is differently directed from each of the light beams (108). Optical device (100).

2. The plurality of light beams (108) each have a different path length (118) within the retroreflector (112). The optical device (100) according to Claim 1.

3. The plurality of light beams (108) are at least partially located within one plane (300) between the optical subsystem (104) and the optical sheet optical system (122). The optical device (100) according to Claim 1 or 2.

4. A portion of the light beam (108) directed from the beam output side (116) to the optical sheet optical system (122) is emitted from the common point (110). The optical device (100) according to any one of Claims 1 to 3.

5. An optical sheet (102) generated from a plurality of different light beams (108) each has a different propagation direction (126). The optical device (100) according to any one of Claims 1 to 4.

6. The light sheets are on the same plane. The optical device (100) according to any one of claims 1 to 5. **Claim 7** The beam input side (114) and the beam output side (116) coincide. The optical device (100) according to any one of claims 1 to 6. **Claim 8** The common point (110) coincides with the beam input side (114). The optical device (100) according to any one of claims 1 to 7. **Claim 9** In at least some of the plurality of light beams (108), a portion (134) of the light beam (108) incident on the retroreflector (112) that ends at the beam input side (114) and a portion (136) of the same light beam (108) exiting the retroreflector (112) that starts at the beam output side (116) are congruent. The optical device (100) according to any one of claims 1 to 8. **Claim 10** The retroreflector (112) has two mirrors (138, 140) inclined to each other. The light beam (108) has an inversion point (142) within the retroreflector (112) where the direction of the light beam (108) is inverted. The optical device (100) according to any one of claims 1 to 9. **Claim 11** The common point (110) reached by the plurality of light beams (108) is located within the rear focal plane (150) of the light sheet optical system (122) or within a plane optically conjugate to the rear focal plane (150). The optical device (100) according to any one of claims 1 to 10. **Claim 12** The light of the plurality of light beams (108) has a coherence length (154) shorter than the shortest difference (156) between the optical path lengths (118) of the plurality of light beams (108). The optical device (100) according to any one of claims 1 to 11. **Claim 13** The optical subsystem (104) has an optical device (160) configured to split one input beam into the plurality of light beams (108). The optical device (100) according to any one of claims 1 to 12. **Claim 14** The optical device (160) has a lens assembly (162) having at least one cylindrical lens (163). The optical device (100) according to claim 13. **Claim 15** A light-sheet microscope (180) having the optical device (100) according to any one of claims 1 to 14 in an illumination beam path (182).

16. A retrofit kit for a light-sheet microscope (180), wherein the retrofit kit has an optical subsystem (104), the optical subsystem (104) has a plurality of collimated light beams (108) at an output side (106) of the optical subsystem (104), and the plurality of collimated light beams (108) reach one common point (110); the retrofit kit has a retroreflector (112), the retroreflector (112) has a beam input side (114) where the light beam (108) is incident on the retroreflector (112) and a beam output side (116) where the light beam (108) exits the retroreflector (112); a path length (118) traversed by the light beam (108) between the beam input side (114) and the beam output side (116) within the retroreflector (112) depends on an incident angle (120) of each of the light beams at the beam input side (114); the retrofit kit is configured to be deployable in an illumination beam path (182) of the light-sheet microscope (184). Retrofit kit.

17. A method for generating a light sheet (102) using the optical device (100) according to any one of claims 1 to 14, wherein a plurality of collimated light pulses (158a, 158b) reaching one common point are incident on a retroreflector (112), traverse a path length (118) depending on an incident angle (120) within the retroreflector (112), and then exit from the retroreflector (112) and are each transformed into one light sheet (102). Method.

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