METHOD, OPTICAL DEVICE AND RETROFIT KIT FOR THE PRODUCTION OF LIGHT LEAFS BY MEANS OF A RETROREFLECTOR

Description

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

[0002] A light sheet can be created by focusing a light beam, especially a laser beam, in only one spatial direction. This type of focusing creates a light disk that illuminates only a thin layer of a sample. The thickness of a light sheet is typically between a few hundred nanometers and a few micrometers.

[0003] To scan the sample or to avoid shadows, several differently oriented light sheets are generated. This typically involves mechanisms with moving elements, such as movable mirrors. These mechanisms are expensive, difficult to adjust, and prone to errors.

[0004] WO 2020 / 063895 describes a device for generating multiple light sheets that illuminate a sample at different planes. For this purpose, a light sheet is formed from an input light beam at a cylindrical lens. Furthermore, a movable scanning mirror or retroreflector and a modulating encoder device are used.

[0005] It is therefore desirable to create devices and methods that allow light sheets to be produced easily and that are not susceptible to wear.

[0006] According to one aspect of the invention, this is made possible by an optical device for generating light sheets, comprising an optical subsystem which has at its output a plurality of collimated light beams which converge towards a common point, comprising a retroreflector which has a beam inlet at which the light beams are coupled into the retroreflector, and a beam outlet at which the light beams exit from the retroreflector, wherein the path length traveled by the light beams in the retroreflector between the beam inlet and the beam outlet is dependent on the angle of incidence of the respective light beam at the beam inlet, and comprising a light sheet optic into which the light beams emanating from the beam outlet of the retroreflector extend, wherein at an output of the light sheet optic each light beam forms a differently oriented light sheet.

[0007] According to a further aspect of the invention, a retrofit kit for a light sheet microscope is provided, comprising an optical subsystem having at its output a plurality of collimated light beams converging to a common point, having a retroreflector having a beam inlet at which the light beams are coupled into the retroreflector, and a beam outlet at which the light beams exit the retroreflector, wherein the path length traveled by the light beams in the retroreflector between the beam inlet and the beam outlet is dependent on the respective angle of incidence of the light beam at the beam inlet, and wherein the retrofit kit is designed to be arranged in the illumination beam path of the light sheet microscope such that the beam outlet of the retroreflector is located in front of the light sheet optics of the light sheet microscope.

[0008] Finally, a method for generating light sheets is provided, preferably using the optical device specified above, in which a plurality of collimated light pulses converging to a common point are coupled into a retroreflector and travel a path length in the retroreflector that depends on the angle of incidence into the retroreflector before they are coupled out of the retroreflector and each transformed into a light sheet.

[0009] With such an optical device, such a retrofit kit and such a method, it is possible to create a plurality of light sheets without the use of wear-prone mechanisms or complex optical devices.

[0010] The advantage here is that the light rays are collimated in the retroreflector, so that the light sheets can be sharply focused even over long path lengths. Thanks to the collimated light rays converging to a single point, standard light sheet optics can be used to generate the light sheets. The path length, which depends on the angle of incidence, makes it particularly suitable for use with pulsed light sources, as different path lengths lead to time-of-flight differences and thus to light sheets that are generated at different times. This can be used to generate incoherent light sheets from light rays that were still coherent in front of the retroreflector, or to generate light sheets that are staggered in time and space, for example in a depth direction. Overall, this results in a device that generates a plurality of light sheets instantly and solely by optical means, and is therefore wear-free.

[0011] A light beam in the above sense, in the context of ray optics, represents a beam path of the optical device or retrofit kit, or an optical axis along which a (collimated) beam of rays moves, without the actual presence of a photon beam or an electromagnetic wave moving along the light beam. The beam path and light rays are also present when the optical device is not in operation. Since light moves along the light rays, the term "light beam" is used below to refer to both the beam path and the light moving along the beam path.

[0012] The invention can be further improved by the following features, each of which is advantageous in itself, independent of one another, and can be combined with one another in any desired way. Each feature can be used indiscriminately for the optical device, the retrofit kit, and the method.

[0013] According to a first advantageous embodiment, the light rays, in particular all light rays, can have different path lengths in the retroreflector.

[0014] It is also advantageous if each light beam enters the retroreflector at a different angle of incidence. The angle of incidence is the angle between the light beam and the normal to the mirror surface of the retroreflector, which the light beam strikes.

[0015] To ensure that each light ray travels a different path length in the retroreflector when converging to a point, the path length of a light ray in the retroreflector can be a strictly monotonic function of the angle of incidence. Thus, the smaller the angle of incidence, the shorter the path length.

[0016] These three measures independently lead to the fact that, due to the different path lengths, each light beam enters the light sheet optics at a different time and can therefore be distinguished both in terms of its position and orientation with respect to the optical axis and in terms of its phase position and can therefore be used specifically to generate certain light sheets.

[0017] In a further advantageous embodiment, it can be provided that the light rays extend at the beam exit at the same angle relative to each other as at the beam entrance. This includes the two possibilities: the light rays converge at the beam exit toward the common point, and the light rays diverge from the common point. Both have the advantage that the retroreflector does not impair the relative path of the light rays. In particular, the portion of the light rays directed from the beam exit to the light sheet optics can originate from the common point.

[0018] In one embodiment, the optical device or retrofit kit is used to generate light sheets that overlap in such a way that shadows caused by the sample are reduced or even eliminated. For this purpose, it is advantageous if the light sheets generated from the different light beams have different propagation directions. Alternatively, or cumulatively, the light sheets can be coplanar.

[0019] Individual, preferably all, light rays can lie at least partially in a plane between the optical subsystem and the light-sheet optics, i.e., they can be coplanar with each other. In particular, the light rays lie adjacent to each other directly in front of (i.e., on the light source side) the light-sheet optics in a direction or plane that is parallel to the spatial direction in which the light rays are focused, for example, by a cylindrical lens of the light-sheet optics. In this way, in conjunction with an objective lens of the light-sheet optics, coplanar light sheets with different orientations are generated.

[0020] The light beams should also be collimated at the beam exit so that the foci of the light sheets are not at different distances from the lens.

[0021] A compact design can be achieved when the beam entrance and exit coincide, meaning the light rays enter the retroreflector at the same point where they exit the retroreflector. With such a design, a beam splitter can be provided between the beam exit and the light-sheet optics. Light rays exiting the retroreflector are preferentially redirected by the beam splitter toward the light-sheet optics. Light rays directed toward the beam entrance can pass through the beam splitter.

[0022] According to a further advantageous embodiment, the common point can coincide with the beam entrance. This allows the dimensions of the beam entrance to be kept small. The common point can, in particular, be located on a mirror surface of the retroreflector. The common point preferably lies on the optical axis of the optical subsystem, which preferably coincides with the optical axis of the light-sheet optics.

[0023] For a compact design of the optical device or retrofit kit, it is advantageous if, for at least some of the light beams, a part of the light beam entering the retroreflector ending at the beam inlet and a part of the same light beam exiting the retroreflector beginning at the beam outlet are congruent.

[0024] According to a particularly simple and compact design, the retroreflector can have two flat mirrors and / or two mirrors tilted relative to one another by only one spatial direction. The light rays can have a reversal point in the retroreflector at which the direction of propagation of the light rays is reversed. In this embodiment, the light rays are reflected in the retroreflector up to the reversal point, initially away from the beam inlet and then, from the reversal point, back to the beam inlet. The mirrors can be spaced apart from one another at any point. The mirrors are preferably spaced closer together at the reversal point than at the beam inlet and / or the beam outlet. To keep the overall size small, the beam inlet and beam outlet can be arranged at the same end of the retroreflector. The reversal point is spaced apart from the beam inlet and beam outlet towards the other end.The distance of the reversal point from the beam entrance and / or beam exit can depend on the angle of incidence of the light beam.

[0025] In order to generate the largest possible path lengths or path length differences in the retroreflector, the angle by which the mirrors are tilted relative to one another is preferably smaller than the angle between the furthest apart light rays. For example, the angle by which the mirrors are tilted relative to one another can be less than 10 -2 rad and / or greater than 10 -4 rad. In another embodiment, the angle by which the mirrors are tilted relative to one another is less than 10 degrees or less than 5 degrees. The angle by which the mirrors are tilted relative to one another determines the path length difference between the light rays in the retroreflector. The path length difference, and thus the angle by which the mirrors are tilted relative to one another, is in most cases adjusted depending on the coherence length of the light from the light source.

[0026] According to a further embodiment, it can be provided that the angle of incidence of at least some, preferably all, light rays is a different integer multiple of the angle by which the mirrors are tilted relative to each other. With such an embodiment, the light rays entering the retroreflector at the beam inlet and those leaving the retroreflector at the beam outlet are congruent.

[0027] The optical device or retrofit kit can comprise a particularly motorized adjustment device designed to adjust the angle between the mirrors. An electronic control unit can be provided to control the adjustment device. The adjustment device can comprise a drive element, for example a motor or other actuator, which acts on at least one mirror. The adjustment device allows the relative position and / or orientation and / or the light rays incident on the light sheet optics and / or the path lengths and / or the path length differences in the retroreflector to be adapted to the respective requirements.For example, the angle by which the two mirrors of the retroreflector are tilted relative to each other can be automatically changed by means of the adjustment device depending on a coherence length of the light of the light rays, a spectrum of the light of the light rays and / or the number, orientation and / or position of the light sheets to be generated.

[0028] Between the two mirror surfaces, the retroreflector can have a volume filled with a gaseous medium or a vacuum, which can be sealed to the outside. Alternatively, the light rays in the retroreflector can also extend through glass. For example, the retroreflector can be made of glass, in particular from a single glass block, for example, in a monolithic construction. Mirrors can be applied to two opposing surfaces of the glass block, or two opposing surfaces of the glass block can be mirrored.

[0029] The common point toward which the light rays converge is preferably located in a rear (light source-side) focal plane or an optically conjugate plane of the light-sheet optics, in particular a cylindrical lens of the light-sheet optics. The cylindrical lens can be located at the end of the light-sheet optics facing the retroreflector, i.e., at its entrance. The cylindrical lens can be located, in particular, between the retroreflector and a microscope objective.

[0030] The optical device and the retrofit kit can be used to generate the light sheets from originally coherent light beams and to superimpose them coplanarly without interference. Such an overlap can, for example, serve to avoid shadows. According to an advantageous embodiment, this can be achieved by ensuring that the shortest difference between the path lengths of different light beams is greater than the coherence length of the light of the light beams. To avoid shadows, the light sheets are preferably coplanar.

[0031] The light source may be part of the optical device.

[0032] It is further advantageous if the light source is designed to generate light pulses, or if the light source is a pulsed light source. In this design, the optical device, in particular the retroreflector, is designed to generate temporally successive light pulses along the light beams from originally synchronous light pulses along the light beams at the beam inlet due to the different path lengths in the retroreflector at the beam exit. The time interval between the successive light pulses results from the path length difference in the retroreflector. The light sheet optics are designed to generate temporally successive, pulsed light sheets from the temporally successive light pulses propagating along the light beams. The light pulses along different light beams are offset from one another in time at the beam exit of the retroreflector.The light sheets are generated from light pulses that reach the light sheet optics one after the other. This allows a sample to be scanned using multiple consecutive light sheets without the need for error-prone mechanical devices.

[0033] The light source is preferably a laser, for example a gas laser or a diode laser.

[0034] The optical subsystem can be configured to split an input beam, for example, a laser beam, into light beams. For example, the optical subsystem can comprise a particularly linear lens arrangement, in particular a microlens arrangement, and / or one or more beam splitters, such as gratings or semi-transparent mirrors, which can also be arranged in a cascade. The lenses of the lens arrangement can be cylindrical lenses. The use of cylindrical lenses in the optical subsystem is not necessary if the light-sheet optics comprises a cylindrical lens.

[0035] At the output of the optical subsystem, the light rays are preferably located next to each other in one plane.

[0036] The optical subsystem may have a lens or a lens system at its output through which the light rays pass and which ensures collimation of the light rays and deflects the individual light rays according to their distance from the optical axis so that they pass through the common point on the optical axis.

[0037] In order to generate collimated light beams, the optical subsystem may comprise a collimation device.

[0038] The optical device in one of the above-described embodiments can be part of a microscope and, in particular, can be arranged in the illumination beam path. The microscope can have detector optics whose optical axis is preferably aligned perpendicular to the plane of the light sheets generated by the light sheet optics.

[0039] In a further embodiment, the microscope may comprise a light source configured to generate light with a predetermined coherence length, wherein the light rays are generated from the light of the light source.

[0040] The invention is explained below using an embodiment as an example with reference to the drawings. In the description and the drawings, the same reference numerals are used for features that correspond to one another in terms of structure and / or function.

[0041] Subject to the above explanations, individual features implemented in the exemplary embodiment may be omitted if their technical effect is not important for a specific application. Conversely, features from the above description of the exemplary embodiment may be added if the technical effect associated with these features is important for a specific application.

[0042] They show: Fig. 1 is a schematic representation of an embodiment of an optical device; Fig. 2 is a schematic representation of the optical device in the viewing direction II-II of the Fig. 1 ; Fig. 3 a schematic plan view of the optical device of the Fig. 1 along arrow III; Fig. 4 shows a schematic representation of a flow chart for a method for producing light sheets.

[0043] The structure and function of an optical device 100 are described below with reference to Fig. 1 to 3 explained.

[0044] The optical device 100 serves to generate a plurality of light sheets 102. Preferably, the optical device 100 serves to generate coplanar and incoherent light sheets 102, which have a different propagation direction 126, from light beams 108, in particular light pulses 158, 158a, 158b. A light sheet 103 is generated from each light beam 108. Alternatively, the optical device 100 can also be used to generate parallel and spaced-apart light sheets 102 from the light beams 108.

[0045] The optical device 100 comprises an optical subsystem 104, which has a plurality of collimated light beams 108 at its output 106, which converge toward a common point 110. A light beam 108 represents an optical axis along which a collimated beam of rays travels. The light beams are preferably arranged adjacent to one another in a plane at the output of the optical subsystem, where they leave the optical subsystem toward the retroreflector 112.

[0046] At its output 106, the optical subsystem 104 may have a lens 107 which ensures that the light rays 108 leaving the optical subsystem 104 toward the retroreflector 112 are collimated and converge toward the point 110.

[0047] The optical device 100 further comprises a retroreflector 112. The light rays 108 are coupled into the retroreflector 112 at a beam inlet 114 of the retroreflector 112. The light rays 108 exit the retroreflector 112 again at a beam outlet 116. Between the beam inlet 114 and the beam outlet 116, the light rays travel a path length 118 in the retroreflector, which depends on an angle of incidence 120 of the respective light beam at the beam inlet 114.

[0048] Fig. 1 shows two light beams as an example. However, the number of light beams 108 can be arbitrarily large and depends, for example, on the respective application of the optical device 100 and the number of required light sheets 102. The path lengths 118 are in Fig. 1They are shown unrolled to the right of the retroreflector 112 to facilitate comparison of their path lengths. In fact, the path length 118 is determined by the zigzag-shaped beam path of the respective light beam 108 in the retroreflector 112.

[0049] The optical device 100 further includes a light sheet optic 122 into which the light rays 108 extend from the beam output 116 of the retroreflector 112. The light sheet optic 122 generates differently oriented light sheets 102 from the light rays 108 at its output 124.

[0050] The optical device 100 can be part of a light sheet microscope 180 and, for example, form an illumination beam path 182 of the light sheet microscope 180 or be arranged in the illumination beam path.

[0051] The optical device 100 can also be configured as a retrofit kit for a light sheet microscope 180 that is not yet equipped with an optical device 100. The retrofit kit comprises the optical device 100 or its components that are yet to be assembled and is configured to be arranged in the illumination beam path 182 of the light sheet microscope.

[0052] The light sheet microscope 180 can be equipped with a detector optics 184 whose optical axis 186 is aligned perpendicular to the optical axis 188 of the light sheet optics 122.

[0053] The optical device 100 may include a light source 152. The light source 152 may be a pulsed light source that generates light pulses 158. For example, the light source may be a laser, such as a gas laser or a diode laser.

[0054] The light source 152 preferably generates light with a coherence length 154, which depends on the design and / or operating mode of the light source.

[0055] In the illustrated variant, the optical subsystem 104 is configured to generate a plurality of light beams 108 from an input light beam 170. For this purpose, an optical device 160 for splitting the light beam can be provided, for example, a particularly linear lens arrangement 162, such as a microlens arrangement, and / or an arrangement of beam splitters, such as gratings or partially transparent mirrors. The beam splitters can also be arranged in a cascade. Fig. 1 A microlens array is shown merely as an example. The lenses 163 of the lens array 162 can be cylindrical lenses. In this case, the light rays are focused in the plane of the drawing and collimated perpendicularly to it.

[0056] If lenses 163 of lens arrangement 162 are cylindrical lenses, then the sole use of a lens 107 would focus the rays collimated perpendicular to the plane of the drawing (approximately to point 110), which is undesirable. Therefore, in this case, another (cylindrical) lens or an arrangement of (cylindrical) lenses can advantageously be provided on the source side of lens 107, which focus in the direction perpendicular to the plane of the drawing into the rear (light source-side) focal plane of lens 107, but focus more strongly than lens arrangement 162 or its lenses 163 in the plane of the drawing, so that a light sheet is created in the sample.

[0057] If a light pulse 158 is generated by the light source 152 along the input light beam 170, it is split by the optical device 160 into different light pulses 158a, 158b, which can in particular be synchronous with one another and propagate along the different light beams 108.

[0058] As can be seen from the Fig. 1 and 3 As can be seen, the individual light beams 108 lie at least in sections, preferably over the entire illumination beam path 182, but at least before entering the light sheet optics 122 next to each other in a plane 300, which in Fig. 3 perpendicular to the plane of the drawing sheet and indicated by a dashed line. In particular, the light rays 108 between the beam exit 116 of the retroreflector 112 and the light sheet optics 122 also lie in a plane, preferably the plane 300, or a plane rotated thereto.

[0059] The light sheet optics 122 has a rear focal plane 150 or a plane optically conjugate thereto, in which the point 110 is located, toward which the collimated light rays 108 generated by the optical subsystem 104 converge.

[0060] The light sheet optics 122 may include a cylindrical lens 164. The point 110 may, in particular, be located in the rear focal plane 150 or a plane optically conjugate thereto of this cylindrical lens 164.

[0061] Furthermore, the light sheet optics 122 may have an objective 166, which may also be referred to as a microscope objective. In a pupil 200 ( Fig. 2 ) of the lens 166, the light rays 108 lie next to each other. The light propagating along the light rays 108 has an elliptical cross-section 202 at each light ray 108 in the pupil 200.

[0062] The light sheets 122 generated by the light sheet optics intersect. The light sheets 102 are preferably arranged coplanar to one another and have a different propagation direction 126. The propagation directions 126 of the light sheets 102 thus lie in a common plane. The light sheets then preferably intersect in a sample volume 168, which can in particular lie on the optical axis 186 of the detector optics 184. This is the case, for example, when the plane 300 runs parallel to a plane 190 in which the cylindrical lens 164 focuses. Fig. 1 this is the drawing sheet layer.

[0063] The cylindrical lens 164 produces elliptical foci, as in Fig. 2The elliptical cross-section of the foci rotates 90 degrees as they pass through lens 166. The light sheets then lie on top of each other and are more strongly focused, i.e., thinner, in the direction along the long axis of the ellipses. This can also be described as several light sheets with elliptical cross-sections lying parallel to each other in the rear focal plane of the lens, i.e., on the light source side. The ellipses are rotated 90 degrees after passing through lens 166 and then lie on top of each other in the focal plane of the lens.

[0064] Coplanar and mutually pivoted light sheets 102 avoid stripe artifacts caused by shadowing and refraction of a light sheet due to objects in the sample volume 168. The sample volume 168 is illuminated from different angles, but coplanarly, by the light sheets 102, so that shadows are minimized.

[0065] When overlapping light sheets 102, care should be taken to ensure that the individual light sheets 102 are incoherent with each other to avoid interference. This is achieved simply by ensuring that the smallest path length difference 156 between all light beams 108 used to generate light sheets 102 is greater than the coherence length 154 of the light of the light beams 108.

[0066] For example, if the light source 152 generates a temporal, t, sequence of input light pulses 158 with a coherence length 154, the individual light pulses 158a, 158b used to generate light sheets 102, into which an input light pulse 158 is split by the optical subsystem 104, should be spaced apart from each other in time by at least one coherence length 154.

[0067] The retroreflector 112 thus serves to generate mutually incoherent light beams 108 at the beam output 116 from mutually coherent light beams 108 at the beam input 114.

[0068] This is achieved by coupling the light rays 108 into the retroreflector 112 at different angles of incidence 120, and the path length 118 in the retroreflector 112 is dependent on the angle of incidence 120. The retroreflector 112 thus converts a difference in the angle of incidence 120 into a path length difference 156. The light propagating along the light rays 108 is incoherent if all path length differences 156 between the light rays 108 in the retroreflector 112 are greater than the coherence length 154.

[0069] In principle, the retroreflector 112 can have any desired design, for example, as a triple mirror or triple prism, as a cat's eye, or as a Lüneburg lens. However, it is preferred that the retroreflector be configured to generate large path length differences 156 between adjacent light beams even with small changes in the angle of incidence of these light beams. Furthermore, it is preferred that the angular relationships that exist between the individual collimated light beams at the beam inlet 114 are also maintained at the beam outlet 116. The retroreflector 112 should therefore not change the relative position and orientation of the individual light beams 108 to one another. Finally, it would be advantageous if the beam inlet 114 were not far from the beam outlet 116 of the retroreflector 112, so that a compact design remains possible.

[0070] The Fig. 1The retroreflector 112 shown as an example meets these requirements.

[0071] In the illustrated embodiment, the retroreflector 112 has two plane mirrors 138, 140 that are tilted relative to one another from their parallel position by an angle 144, which is preferably between 10 -4 and 10 -2 radians. Angles of less than 10 degrees or less than 5° are also possible. The axis about which the two mirrors 138, 140 are tilted relative to one another is perpendicular to the plane 300 and runs parallel to the mirror planes. The volume 192 between the two mirrors can be filled with gas or air and sealed to the outside. Alternatively, the retroreflector 112 can also be made from a glass block, so that the light rays 108 in the retroreflector 112 extend through glass. In this case, the mirrors 138, 140 are formed by two opposing surfaces of the glass block that are tilted relative to one another.

[0072] In the illustrated embodiment, the beam entrance 114 is located on the surface 132 of a mirror 138. A center plane 148 between the two mirrors 138, 140, which is equally spaced from the opposing mirrors 138, 140, is perpendicular to the plane 300 and runs obliquely to the illumination beam path 182.

[0073] The point 110, to which the collimated light beams 108 converge, can be located in front of or inside the retroreflector 112. In the Fig. 1 In the embodiment shown, point 110 is located on the mirror surface 132, i.e. at the beam entrance 114. The beam exit is also located at this point.

[0074] In Fig. 1 the beam paths of two light beams 108 in the retroreflector 112 are shown schematically.

[0075] The light rays 108 are reflected back and forth between the two mirrors 138, 140. As the distance between the two mirrors decreases in the direction away from the beam entrance, the light rays 108 are reflected away from the beam entrance into the reflector 112. Due to the angle 144, the angle of incidence decreases increasingly with each reflection from one of the mirrors 138, 140. As the number of reflections increases, the light rays 108 fall increasingly steeply onto the mirrors 138, 140 until, at a reversal point 142, the direction of the light beam 108 reverses in the retroreflector 112, and the light beam 108 is reflected back to the beam entrance 114.

[0076] On the path from the reversal point 142 to the beam entrance 114, the angle of incidence on the mirrors 138, 140 increases again with each reflection from one of the mirrors 138, 140. At the beam entrance 114, the retroreflected light beam 108 leaves the retroreflector 112 again.

[0077] At the Fig. 1 In the embodiment shown, beam inlet 114 and beam outlet 116 therefore spatially coincide.

[0078] If the zigzag reflection of the light rays 108 in this retroreflector 112 is considered a spatial wave, the frequency of this spatial wave increases until the reversal point, before decreasing again. Due to the very small angle 144, a high number of reflections occurs, so that the path length difference 156 can be adjusted to the coherence length 154 by adjusting the angle 144.

[0079] If the angle of incidence of a light beam 108 at the beam entrance 114 is an integer multiple of the angle 144, the light beam 108 is reflected back congruently in the retroreflector 112. In one embodiment of the optical device 100, all angles of incidence 120 of the light beams are therefore an integer multiple of the angle 144. The light beam 134, 108 incident on the retroreflector 112 is thus congruent with the retroreflected light beam 136, 108.

[0080] A beam splitter 130 in the illumination beam path 182 reflects the light beams 108, 136 coming from the beam exit 116 to the light sheet optics 122, while the light beams 108, 134 propagating in the direction of the beam entrance 114 pass through the beam splitter 130.

[0081] Due to the different lengths of reflection paths in the retroreflector 112, the light rays 108 entering the light sheet optics 122 are offset in time from one another or decoherent, as already explained above.

[0082] According to Fig. 4 To generate light sheets, in a first step 400, a plurality of collimated light pulses 158a, 158b converging toward the common point 110 are coupled into a retroreflector 112. In step 402, the light pulses travel a path length 118 in the retroreflector 112 that depends on their angle of incidence 120.

[0083] They are then decoupled from the retroreflector 112 in a step 404 and each transformed into a light sheet 102. The light sheets 102 can be generated in a step 406 in a coplanar manner and with different propagation directions that intersect in a sample volume 168.

[0084] 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 acting on at least one of the mirrors 138, 140, for example, a motor or actuator, and a control device 198 controlling the drive element 196. By adjusting the angle 144, the number of light sheets 102 or the path length difference 156, for example, can be adjusted.

[0085] The term "and / or" includes all combinations of one or more of the related listed elements and may be abbreviated as " / ".

[0086] Although some aspects have been described in the context of a device, it is clear that these aspects also represent a description of the corresponding method, with a block or device corresponding to a method step or a function of a method step. Analogously, aspects described in the context of a method step also represent a description of a corresponding block, element, or property of a corresponding device. Reference symbol

[0087] 100optical device 102light sheet 104optical subsystem 106output of the optical subsystem 107lens at the output of the optical subsystem 108light beam 110common point towards which light rays converge 112retroreflector 114beam entrance of the retroreflector 116beam exit of the retroreflector 118path length of a light beam in the retroreflector 120angle of incidence of a light beam into the retroreflector 122light sheet optics 124exit of the light sheet optics 126direction of propagation of a light sheet 130beam splitter 132mirror surface 134section of the light beam 136section of the light beam 138mirror 140mirror 142point of reversal 144angle by which mirrors are tilted relative to each other 146time offset 148center plane 150rear focal plane of the light sheet objective orof the light sheet optics 152Light source 154Coherence length 156Path length difference 158Input light pulse 158a, 158bLight pulses generated from the input light pulse 160Optical device for splitting a light beam 162Lens arrangement 163Cylindrical lens of the lens arrangement 164Cylindrical lens 166Objective lens 168Sample volume 170Input light beam 180Light sheet microscope 182Illumination beam path 184Detector optics 186Optical axis of the detector optics 188Optical axis of the light sheet optics 190Plane focused in the cylindrical lens 192Volume between the mirrors 194Adjustment device 196Drive element 198Control device 200Pupil 202Elliptical cross-section 300Plane of the light rays 400Coupling of the Light rays 402Reflecting light rays depending on the angle of incidence 404Creating a light sheet 406Creating coplanar, intersecting light sheets.

Claims

1. Optical apparatus (100) for producing light sheets (102), with an optical subsystem (104) having at its outlet (106) a plurality of collimated light beams (108), converging to a common point (110), with a retroreflector (112) having a beam inlet (114) at which the light beams (108) are coupled into the retroreflector (112) and a beam outlet (116) at which the light beams (108) exit from the retroreflector (112), wherein the path length (118), traveled in the retroreflector (112) by the light beams (108) between the beam inlet (114) and the beam outlet (116), is dependent on the respective angle of incidence (120) of the light beam at the beam inlet (114), and with a light sheet optic (122) into which the light beams (108) emanating from the beam outlet (116) of the retroreflector (112) extend, wherein at an outlet (124) of the light sheet optic (122) a differently oriented light sheet (102) is formed from each light beam (108).

2. The optical apparatus (100) according to claim 1, wherein the light beams (108) have different path lengths (118) in the retroreflector (112).

3. The optical apparatus (100) according to claim 1 or 2, wherein the light beams (108) lie at least partially in a plane (300) between the optical subsystem (104) and the light sheet optic (122).

4. The optical apparatus (100) according to any one of claims 1 to 3, wherein the part of the light beams (108) directed from the beam outlet (116) to the light sheet optic (122) emanates from the common point (110).

5. The optical apparatus (100) according to any one of claims 1 to 4, wherein the light sheets (102), produced from the different light beams (108), have different propagation directions (126).

6. The optical apparatus (100) according to any one of claims 1 to 5, wherein the light sheets are coplanar.

7. The optical apparatus (100) according to any one of claims 1 to 6, wherein the beam input (114) and the beam outlet (116) coincide.

8. The optical apparatus (100) according to any one of claims 1 to 7, wherein the common point (110) coincides with the beam inlet (114).

9. The optical apparatus (100) according to any one of claims 1 to 8, wherein for at least some of the light beams (108), a part (134) of the light beam (108) entering the retroreflector (112) ending at the beam inlet (114) and a part (136) of the same light beam (108) exiting from the retroreflector (112) beginning at the beam outlet (116) are congruent.

10. The optical apparatus (100) according to any one of claims 1 to 9, wherein the retroreflector (112) has two mirrors (138, 140) tilted relative to one another, and the light beams (108) in the retroreflector (112) have a reversal point (142) in which the direction of the light beams (108) is reversed.

11. The optical apparatus (100) according to any one of claims 1 to 10, wherein the common point (110) to which the light beams (108) converge lies in a rear focal plane (150) or a plane of the light sheet optic (122) that is optically conjugate thereto.

12. The optical apparatus (100) according to any one of claims 1 to 11, wherein the light of the light beams (108) has a coherence length (154) which is smaller than the shortest difference (156) between the path lengths (118) of the light beams (108).

13. The optical apparatus (100) according to any one of claims 1 to 12, wherein the optical subsystem (104) comprises an optical apparatus (160), configured to split an input beam into the light beams (108).

14. The optical apparatus (100) according to claim 13, wherein the optical apparatus (160) comprises a lens arrangement (162) with at least one cylindrical lens (163).

15. Light sheet microscope (180) with an optical apparatus (100) according to any one of claims 1 to 14 in the illumination beam path (182).

16. Retrofit kit for a light sheet microscope (180), with an optical subsystem (104) having at its outlet (106) a plurality of collimated light beams (108), converging to a common point (110), with a retroreflector (112) having a beam inlet (114) at which the light beams (108) are coupled into the retroreflector (112) and a beam outlet (116) at which the light beams (108) exit the retroreflector (112), wherein the path length (118), travelled in the retroreflector (112) by the light beams (108) between the beam inlet (114) and the beam outlet (116), is dependent on the respective angle of incidence (120) of the light beam at the beam inlet (114), and wherein the retrofit kit is configured to be arranged in the illumination beam path (182) of the light sheet microscope (184) such that the beam outlet (116) of the retroreflector (112) is located in front of the light sheet optic (122) of the light sheet microscope (184).

17. Method for producing light sheets (102), preferably using an optical apparatus (100) according to one of claims 1 to 14, in which a plurality of collimated light pulses (158a, 158b) converging to a common point, are coupled into a retroreflector (112) and travel a path length (118) in the retroreflector (112) which depends on the angle of incidence (120) into the retroreflector (112) before they are coupled out of the retroreflector (112) and each converted into a light sheet (102).