Abstract:
A light-scanning microscope including a scan optics for generating a pupil plane conjugate to the pupil plane of the microscope objective, and a variably adjustable beam deflection unit in the conjugate pupil plane. An intermediate image lies between the microscope objective and the scan optics. The scan optics image a second intermediate image (Zb 2 ) into the first intermediate image via the beam deflection unit, wherein the second intermediate image is spatially curved. The deflection unit is not arranged in a collimated section of the beam path, but is instead arranged in a convergent section. Then, in terms of the optical properties and quality thereof, the scan optics needs rather to correspond merely to an eyepiece instead of a conventional scanner objective.

Description:
[0001]    The present application claims priority from International Patent Application No. PCT/EP2015/058328 filed on Apr. 16, 2015, which claims priority from German Patent Application No. 10 2014 005 880.8 filed on Apr. 17, 2014, the disclosures of which are incorporated herein by reference in their entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    It is noted that citation or identification of any document in this application is not an admission that such document is available as prior art to the present invention. 
         [0003]    The invention relates to a light-scanning microscope comprising an optical system, which defines an illumination beam path and comprises the following components: a light source, which provides a spatially restricted light distribution, a microscope objective comprising a (light-source-side) pupil plane and an (objective-side) focus, a scan optics (also referred to as “scan lens”) for generating a pupil plane conjugate to the pupil plane of the microscope objective, and (in respect of the deflection direction) a variably adjustable beam deflection unit (for displacing the focus transversely in relation to an optical axis of the microscope objective), wherein the illumination beam path images at least one point of the light distribution and one point of the focus on one another, wherein the beam deflection unit is arranged in the conjugate pupil plane (optically between the light distribution and the scan optics) and an intermediate image lies optically between the microscope objective and the scan optics. 
         [0004]    The invention moreover relates to a light-scanning microscope comprising an optical system which defines an detection beam path and comprises the following components: a microscope objective comprising an (output) pupil plane and an (objective-side) focus, a scan optics for generating a pupil plane conjugate to the pupil plane of the microscope objective, (in respect of the deflection direction) a variably adjustable beam deflection unit, and an optoelectronic transducer, wherein the detection beam path images at least one point of the focus and at least one respective point of the transducer on one another, wherein the (reflecting surface of the) beam deflection unit is arranged in the conjugate pupil plane (optically between the light distribution and the transducer) and an intermediate image lies optically between the microscope objective and the scan optics. 
         [0005]    The invention moreover relates to similar light-scanning microscopes, in which the scan optics collimates beams coming from the first intermediate image in a conventional manner. 
         [0006]    Within the meaning of the invention, the light is any form of electromagnetic radiation which is manipulable by optical means, in particular including infrared and ultraviolet radiation. For the purposes of providing the light distribution, the light source may comprise, in particular, an optical waveguide and/or a beam shaper. It may moreover comprise an intensity modulator. In particular, the optoelectronic transducer may comprise a stop that is confocal with the focus of the microscope objective. The deflection unit is also referred to as scanner. 
         [0007]    In the prior art, such light-scanning microscopes are known, for example from “Confocal Scanning Optical Microscopy and Related Imaging Systems” by T. R. Corle and G. S. Kino (Academic Press, 1996, Section 2.2.7, FIG. 2.2). Therein, the scan optics is referred to as “scan objective”. It provides a collimated conjugate pupil plane at the location of the deflection unit. The combination of scan optics and tube lens is referred to as transfer optics. 
         [0008]    Moreover, a second variably adjustable beam deflection unit is arranged in a further pupil plane in WO 90/00755 A1, said further pupil plane being generated from a relay optics consisting of concave mirrors. A corresponding arrangement with a micro-electromechanical drive of the deflection unit is known from e.g. US 2013/107338 A1. 
         [0009]    Arranging the deflection unit(s) in a (respective) conjugate object pupil advantageously renders possible the provision of a resting beam cross section in further conjugate pupils. As a result of this, manipulations of the wavefront with a high accuracy are possible, like in US 2003/230710 A1 or in WO 2008/037346 A1. Moreover, the marginal ray stop down by vignetting at the optics is minimal in this way. 
         [0010]    However, the light-scanning microscopes described above are disadvantageous in that the scan optics, which is required for generating the conjugate pupil plane, is complicated and not light efficient since it needs to compensate various image aberrations, such as field curvature and transverse chromatic aberration, in order to allow a high imaging quality. Moreover, there is little available installation space for the deflection unit due to the small distance between the conjugate pupil plane and the scan optics. 
       SUMMARY OF THE INVENTION 
       [0011]    The invention is based on the object of improving a microscope of the type set forth at the outset such that the scan optics can have a simpler design and it is possible to provide more installation space for the deflection unit. 
         [0012]    According to the invention, provision is made for the scan optics to image a second intermediate image into the first intermediate image via the (reflecting surface of the) beam deflection unit or for the scan optics to image the first intermediate image into the second intermediate image via the (reflecting surface of the) beam deflection unit, wherein the second intermediate image is spatially curved in both cases. Therefore, in contrast to the prior art, the (reflecting surface of the) deflection unit is no longer arranged in a collimated section of the detection beam path, but in a convergent section instead. A virtual object lies downstream of the beam deflection unit due to the reflection at the reflecting surface of the deflection unit. The spatial curvature of the intermediate image allows the provision of the conjugate pupil plane by means of a scanning optics which has been significantly simplified in comparison with the conventional, collimating scanning objectives, in particular without correction of the curvature of field, with, nevertheless, the same imaging quality of the overall optical system. This makes it possible to dispense in particular with the (near field) lenses with negative focal distance/refractive power which were previously conventional for planarization (W. J. Smith: “Modern Lens design”, McGraw-Hill, 1992, chapter 22, page 411). In terms of the optical properties and quality thereof, such a scan optics needs rather to correspond merely to an eyepiece instead of a conventional scanner objective. The radius of curvature of the second intermediate image then preferably corresponds to the distance between the deflection unit and the focal position of the first intermediate image. Additionally, the correction of the transverse chromatic aberration can also be divided among the scan optics and the tube lens within the meaning of a compensation system, meaning a further simplification of the scan optics. Expediently, the microscope can have such an embodiment that the scanning optics and the tube lens compensate one another in respect of the transverse chromatic aberration. 
         [0013]    This arrangement is particularly advantageous in the case of a nonlinear interaction of the excitation radiation with the sample. Here, the quadratic dependence (in the case of the two-photon excitation) or cubic dependence (in the case of the excitation of the third harmonic or the three-photon excitation) of the light emission in the sample on the intensity in the case of the conventional arrangement of a plurality of beam deflection units in a respective pupil in such a way that the deflection units are not imaged on one another leads to problems in the image field illumination. The physical distance of the deflection units upstream of the scan objective will be imaged into the objective pupil with an axial magnification which increases quadratically with a lateral magnification. This leads to a non-stationary pupil, which results in a field-dependent excitation intensity. These problems in nonlinear optics (NLO) can be avoided by arranging the beam deflection unit in a non-collimated pupil since this allows good imaging of the deflection units on one another in a light-efficient arrangement. Typically, the detection of the fluorescence in this case is not brought about by way of the beam deflection unit, but already upstream in the so-called “non-descanned” beam path section. However, since the arrangement is equally effective in the excitation direction as in the detection direction, clean imaging of the pupils is also obtained in this case. 
         [0014]    Preferably, the second intermediate image is spherically curved or at least substantially spherically curved, in particular with a radius of curvature between the single focal length and twice the focal length of the scan optics. Preferably, the radius of curvature of the intermediate image is identical to a distance between (a center point of the reflecting surface of) the deflection unit and the second intermediate image. 
         [0015]    Advantageously, a center of the curvature of the second intermediate image may lie in a beam deflection unit, in particular on a reflecting surface of the relevant beam deflection unit. 
         [0016]    Expediently, the light-scanning microscope may comprise an illumination optics for imaging the light distribution into an intermediate image, in particular into the second intermediate image or into a third or further intermediate image, and/or a detection optics for imaging an intermediate image, in particular the second intermediate image or a third or further intermediate image, into the transducer. 
         [0017]    In particular, the optical system may comprise a beam splitter which is arranged in the illumination beam path and in the detection beam path in such a way that light coming from the focus is decoupled to the optoelectronic transducer from the illumination beam path. 
         [0018]    Expediently, the optical system may comprise a collimation optics (in the illumination beam path or in the detection beam path) on a side of the beam deflection unit distant from the scan optics. In this manner, further manipulations on the beams and the final detection are possible with little outlay. 
         [0019]    Preferably, (exactly) one concave mirror, the center of curvature of which lies in the conjugate pupil plane, lies optically between the beam deflection unit and the light source or the transducer, in particular as a collimation optics. The concave mirror has an achromatic effect. In this manner, a further conjugate pupil plane can be provided with little optical outlay, in particular with a small number of interfaces. By arranging the concave mirror at the distance of the radius of curvature thereof from the first conjugate pupil, it is possible to provide (via a curved second intermediate image) a highly precise image at the same distance, independently of the field angle. 
         [0020]    Advantageously, a radius of curvature R H  of the concave mirror may be twice the size of a radius of curvature R ZB  of the second intermediate image such that plane wavefronts are present downstream of the concave mirror (on the transducer side). In this way, the second conjugate pupil lies in a collimated beam path section and the beam diameters in the two conjugate pupils are the same. Expediently, the concave mirror is then arranged in such a way that rays coming from the focus of the microscope objective (through the second intermediate image) extend parallel to one another downstream of the concave mirror, preferably also parallel to a plane within which the first deflection unit is able to deflect incoming light, and at an angle in relation to a central axis of the concave mirror. The distance A between concave mirror and the curved intermediate image then equals the radius of the intermediate image R H :R H =2·R ZB =2·A. Thus, in conjunction with the curved second intermediate image, a particularly high imaging quality of the optical system is possible with little outlay. However, there may also be wavefront curvatures differing from zero downstream of the concave mirror if the concave mirror radius of curvature R H  deviates from twice the intermediate image radius R ZB  by a difference D. For the concave mirror radius R H =2·R ZB +D, the distance A between concave mirror and intermediate image is A=R ZB +D and the second deflection unit is arranged at the center of curvature of the concave mirror, i.e. at a distance R H  therefrom. Furthermore, the beam diameters on the first beam deflection unit and on the second beam deflection unit may be unequal, for example in the case of an imaging scale not equal to 1:1. 
         [0021]    However, the radius of curvature R H  of the concave mirror may also deviate from twice the radius of curvature R ZB  of the intermediate image. A concave mirror with the radius of curvature R H =A is then arranged at the distance A/2 from the curved intermediate image such that the light on the optical axis is collimated (when the beam deflection units are in the mid-positions thereof) and the light outside extends in a slightly divergent or convergent manner. 
         [0022]    Preferably, the concave mirror, in particular the reflecting surface thereof, has a toric form (surface form of a toroidal section), with the invention also comprising other forms. As a result, the astigmatism resulting from oblique incidence can be reduced. Here, the concave mirror preferably has a first radius of curvature, which is smaller than twice the radius of curvature of the intermediate image by a factor cos (angle of incidence), and a second radius of curvature, which is greater than twice the radius of curvature of the intermediate image by a factor cos(angle of incidence). Preferably, the first curvature belonging to the first radius of curvature extends about an axis which is parallel to an axis of rotation of the first beam deflection unit and the curvature belonging to the second radius of curvature is orthogonal to the first curvature. 
         [0023]    A second aspect of the invention relates to a light-scanning microscope of the type set forth at the outset, in which the scan optics collimates beams, which come from the first intermediate image and originate from the focus, like in the prior art. It solves the problem of being able to set the position of a conjugate objective pupil relative to the beam deflection unit. Under this aspect, the invention provides for a converging optics to be optically arranged between the beam deflection unit and the transducer or the light source, said converging unit focusing the collimated beam coming from the beam deflection unit into a second intermediate image, wherein the scan optics and the converging optics are displaceable along an optical axis of the detection beam path. Here, the scan optics and the converging optics form a finite relay optics. Here, the displaceability renders possible the above-described advantages of adaptability to different microscope objectives; however, the correction of curvature and lateral chromatic aberrations is expedient, like in the prior art. An electric drive for displacing the scan optics and/or the converging optics may be provided. In particular, these may be separate drives for scan optics and converging optics. Here, provision may be made of a control unit which is configured to displace the scan optics and the converging optics in the same sense, in particular over the same distance, in particular in a synchronous or simultaneous manner. 
         [0024]    Advantageous embodiments which are able to be used in all aspects of the invention are described below. 
         [0025]    In preferred embodiments, a second variably adjustable beam deflection unit or a variably adjustable wavefront modulator is arranged in a further conjugate pupil plane between the first beam deflection unit and the transducer, for example like in WO 2008/037346 A1. In particular, the further conjugate pupil plane can be the second pupil plane generated by a concave mirror, or a third pupil plane. The second beam deflection unit may have an axis of rotation which differs from an axis of rotation of the first beam deflection unit. As a result, a two-dimensional field can be scanned on the sample side. Alternatively, the axis of rotation of the second beam deflection unit may be parallel to an axis of rotation of the first beam deflection unit. As a result, one of the two beam deflection units can serve for an approximate setting and the other one can serve for a fine setting of the beam deflection. Moreover, already the first beam deflection unit, optionally the second beam deflection unit too, may provide a variable deflection in two dimensions. Alternatively, both beam deflection units may each be adjustable about precisely one respective axis of rotation in advantageous embodiments, in particular by way of drives that differ from one another or by way of the same drives in different modes of operation. By way of example, both beam deflection units may be embodied as galvanometric scanners, of which only one is operated with resonant oscillation. 
         [0026]    By way of example, precisely one of the two beam deflection units may comprise a resonantly oscillating mirror (“resonance scanner”). In this way, it is possible to scan a line on the sample by means of the resonantly oscillating mirror, which line may be scanned additionally in the longitudinal or transverse direction by means of the other beam deflection unit or in the longitudinal and transverse direction in the case of two-dimensional adjustability. 
         [0027]    An adjustment of the sample-side focal plane along the optical axis (in the z-direction) and hence scanning of a sample in the depth is possible by means of the wavefront modulator within the maximum modulation lift provided thereby. In conjunction with a two-dimensionally variable first beam deflection unit, this enables a three-dimensional displacement of the measurement location and hence three-dimensional scanning of the sample. As an alternative to the displacement of the focus along the optical axis, a spatially resolved adjustable wavefront modulator may also be used to compensate location-dependent imaging aberrations, which e.g. arise from local variations of one or more sample properties. 
         [0028]    To this end, the light-scanning microscope may comprise a control unit which records at least one image of a sample and establishes manipulated variables for the wavefront modulator (and sets the wavefront modulator accordingly) on the basis of at least one predetermined property of the sample which influences the image, in particular an actual distribution of a property in the sample, and on the basis of the image. In particular, the control unit can establish a measured distribution of the sample property on the basis of the image and establish the manipulated values in such a way that a deviation between the measured distribution and the actual distribution is minimal, for example by means of curve fitting. 
         [0029]    Configurations in which some, or all, of the scan optics is displaceable along an optical axis of the detection beam path are particularly preferred. In particular, they may comprise an electric drive for displacing the displaceable part of, or the entire, scan optics. As a result of the axial displacement, the position of the conjugate pupil relative to the first deflection unit is able to be set with little outlay, whereas, previously, the position of the scan objective was only set and fixed once on the beam deflection unit for adjusting the focal position and hence for adjusting the collimation. As a result of this, it is possible, in particular, to compensate a pupil shift, which occurs e.g. when interchanging the microscope objective. Here, the axial position of the conjugate pupil varies with the square of the imaging scale between first deflection unit and objective pupil. Here, the focal position in the intermediate image plane, and hence also in the object plane, are largely maintained. 
         [0030]    Preferably, the scan optics is embodied in such a way that the imaging thereof (from the first intermediate image into the second intermediate image) has a magnification factor of between 0.8 and 1.2, in particular of between 0.9 and 1.1, in particular of exactly 1. In this way, the position of the first intermediate image, and hence the sample-side focal plane, remains constant with a high accuracy. The focus is maintained best in the case of 1:1 imaging of the scan optics from the virtual object to the first intermediate image (parabolic extent of the focal offset). 
         [0031]    Embodiments in which the microscope objective is arranged in a manner displaceable along the optical axis and/or in an objective changer, in particular comprising an electric drive for displacing the microscope objective and/or for interchanging the microscope objective, are advantageous. As a result, great flexibility when measuring with an unchanging high imaging quality is rendered possible in conjunction with the adaptability to the different pupil positions of different objectives. 
         [0032]    Preferably, the first beam deflection unit and/or the second beam deflection unit have/has a micro-electromechanical system for setting the beam deflection. Like in U.S. Pat. No. 7,295,726 B1, this may provide rotatability about two different axes, in particular with the position of the (stationary) point of intersection of these axes in a reflecting surface (deflecting the beam coming from the scan optics), in particular with the arrangement of this point of intersection on the optical axis of the detection beam path. MEMS-based scanners have a significantly lower mirror mass and, as a result thereof, have the advantage of being able to be tilted quickly in any way and with high accuracy. By way of example, one of the beam deflection units may be a MEMS-based mirror which is only adjustable about exactly one axis of rotation and the other beam deflection unit may be a galvanometric scanner. Here, the galvanometric scanner may also be operated resonantly. 
         [0033]    In particular, the invention also comprises light-scanning microscopes with a light source, the light of which is able to be coupled or is coupled optically into the microscope objective via the first beam deflection unit by means of a beam splitter arranged in the detection beam path. Expediently, the light source is a laser. By way of example, it may be a tunable laser. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0034]      FIG. 1  shows a light-scanning microscope. 
           [0035]      FIG. 2  shows a simplified scan optics as scan objective. 
           [0036]      FIG. 3  shows a complete transfer optics. 
           [0037]      FIGS. 4A, 4B, and 4C  show, in three different views, an extended transfer optics with an additional pupil plane. 
           [0038]      FIG. 5  shows a scan optics with a finite relay optics. 
       
    
    
       [0039]    In all of the drawings, parts that coincide bear the same reference signs. 
       DETAILED DESCRIPTION OF EMBODIMENTS 
       [0040]    It is to be understood that the figures and descriptions of the present invention have been simplified to illustrate elements that are relevant for a clear understanding of the present invention, while eliminating, for purposes of clarity, many other elements which are conventional in this art. Those of ordinary skill in the art will recognize that other elements are desirable for implementing the present invention. However, because such elements are well known in the art, and because they do not facilitate a better understanding of the present invention, a discussion of such elements is not provided herein. 
         [0041]    The present invention will now be described in detail on the basis of exemplary embodiments. 
         [0042]      FIG. 1  is a schematic illustration of a light-scanning microscope  10  (“LSM”) which is controlled by means of the control unit  34 . The LSM  10  is put together in a modular manner from two illumination modules L with lasers  23 , a scanning module S, a detection module D and the microscope unit M with the microscope objective  21 . The microscope unit M comprises e.g. an objective revolver for swiveling in different microscope objectives  21 . 
         [0043]    The light from the lasers  23  can be influenced by light doors  24  and attenuators  25  by way of the control unit  34  before it is fed into, and unified in, the scanning unit S by way of fiber optical waveguides  22  and coupling optics  20 , for example in the form of collimation optics. The combination of each laser  23  with the optics up to the respective fiber optical waveguide  22  can be considered to be a respective light source, which provides a confocal, punctiform light distribution, which is imaged in the sample P, at the end of the relevant fiber optical waveguide  22 . 
         [0044]    By way of the principal beam splitter  33  and the beam deflection unit  30 , which is variably adjustable in X-and Y-direction and has a single mirror with an MEMS drive (not depicted here), the excitation light reaches the microscope objective  21 , which focuses the light in the sample P in the measuring location (not depicted here). Excitation light scattered back from the sample P or emitted fluorescence light reaches the detection module D through the microscope objective  21 , the tube lenses  27  and the scan optics  35 , via the deflection unit  30 , through the collimation optics  36  and the principal beam splitter  30 . For the purposes of the fluorescence detection, the principal beam splitter  30  may be embodied e.g. as a dichroic color splitter (“principal color splitter”) such that the back-scattered excitation light is mirrored out in the direction of the lasers  23 . 
         [0045]    Downstream of a detection optics  38 , for example a converging lens, the detection module D comprises a plurality of detection channels, each with a pinhole  31 , a filter  28  and a photomultiplier  32  as an optoelectronic transducer, which are spectrally separated by color splitters  29  (“secondary color splitters”). It is also possible to use slot diaphragms (not depicted here) instead of pinholes  31 , for example in the case of a line-shaped illumination. The detection optics  38  focuses the previously collimated beams onto the confocal pinholes  31 . The confocal pinholes or slot diaphragms  31  serve to discriminate sample light which does not originate from the focus volume at the measurement location. Therefore, the photomultipliers  32  only detect light from the focal volume and thus define the measurement location in the sample P, from which light is recorded and detected at the detection location in the respective light-sensitive layer of the photomultipliers  32 . Alternatively, it is also possible to use other light-sensitive sensors known from the prior art, such as avalanche diodes. 
         [0046]    The measurement volume of the sample P, which is recorded and illuminated confocally, is able to be moved over the sample P by means of the deflection unit  30  in order to record an image pixel-by-pixel by virtue of the MEMS mirror of the deflection unit  30  being twisted in a targeted manner. Both the movement of the MEMS mirror  30  and the switching of the illumination by means of the light doors  24  or the attenuators  25  are controlled directly by the control unit  34 . Recording data from the photomultipliers  32  is effected by the control unit  34 . 
         [0047]    The microscope objective  21  has an infinite back focal length such that e.g. a collimated beam path is present up to the tube lens  27 . Situated within the microscope objective  21  is the (output) pupil plane PE thereof. The tube optics  27  generates a first intermediate image Zb 1 , which is imaged into a second intermediate image Zb 2  by the scan optics  35 . The pupil plane PE′ conjugate to the pupil plane PE lies on the beam deflection unit  30 . As a result, the beam deflection unit  30  lies in a convergent section of the detection beam path. Subsequently, the collimation optics  36  images the second intermediate image Zb 2  to infinity such that only collimated beams are present at the principal beam splitter  33 . In alternative embodiments (not depicted here), convergent or divergent beams may be present at the principal beam splitter  33 . The coupling optics  20  in the scanning module S and the detection optics  29  should then be adapted appropriately. 
         [0048]    By way of example, the scan optics  35  is displaceable along the optical axis of the unified detection and illumination beam path by means of a drive. As a result of this, the position of the conjugate pupil plane PE′ can be kept axially on the beam deflection unit  30 , even in the case of a change in the pupil plane PE in the case of an interchange, or an axial displacement, of the microscope objective  21 . 
         [0049]    A module N (“NLO detection module”) for detecting fluorescence after the nonlinear interaction in the case of the excitation is connected to an additional output provided by a beam splitter  39  (also referred to as “NLO beam splitter”). It is possible to connect the NLO detection module N and use the latter for the measurement as an alternative, or in addition, to the detection module D. In alternative embodiments (not depicted here), an independent NLO detection module with a dedicated microscope objective may be arranged on the opposite side of the sample, and used for the detection, as an alternative, or in addition, to the NLO detection module N. 
         [0050]      FIG. 2  depicts the beam paths around the scan optics  35 , which replaces a conventional, complicated scan objective by virtue of imaging the first intermediate image Zb 1  into a second intermediate image Zb 2 , in detail for three different positions of the beam deflection unit  30 . The scan optics  35  is free from a curvature-of-field correction and has an imaging scale of 1:1. It is possible to identify that the second intermediate image Zb 2  is spatially curved on the basis of the virtual object V behind the beam deflection unit  30  arranged in the conjugate pupil PE′. 
         [0051]      FIG. 3  shows the complete transfer optics which, in addition to the scan optics  35  and the beam deflection unit  30  from  FIG. 2 , also comprises a tube optics  27 . The beam paths from the actual pupil plane PE of the microscope objective (not depicted here) to the second intermediate image Zb 2  are once again depicted for three different positions of the deflection unit  30 . The tube optics  27  focuses the collimated beam coming from the pupil PE into the first intermediate image Zb 1 , which images the scan optics  35  into the spatially curved second intermediate image Zb 2  via the beam deflection unit  30 , which is arranged in the conjugate pupil PE′. 
         [0052]      FIG. 4  depicts, in three different views ( FIGS. 4A, 4B, 4C ), an extended transfer optics with a second conjugate pupil plane PE″ and a second variably adjustable beam deflection unit  30 B. This extended transfer optics replaces e.g. the afocal relay optics according to Kessler, known from the literature, as described in e.g. US 2010/0208319 A1 or WO 90/00755 A1. 
         [0053]    By way of example, the first beam deflection unit  30 A is a single mirror with a MEMS drive, which is rotatable about two mutually orthogonal, stationary axes. The stationary point of rotation of the mirror lies in the reflecting surface of the mirror on the optical axis of the transfer optics. By way of example, the second beam deflection unit  30 A is a single mirror with a galvanometric drive, i.e. it has only exactly one axis of rotation. By way of example, it can be operated in resonant oscillation. Alternatively, it is also possible to insert galvanometric beam deflection units, of which one can move the light in the sample in the x-direction and the other one can move it in the y-direction, into both conjugate pupil planes PE′ and PE″. 
         [0054]    The additional pupil plane PE″ is provided by a collimation optics  36 , which e.g. is configured as a toric concave mirror and arranged optically between the first beam deflection unit  30 A and the second beam deflection unit  30 B. The first center of curvature of the concave mirror lies in the first conjugate pupil plane PE′ on the reflecting surface of the first beam deflection unit  30 A (distance R between concave mirror and conjugate pupil PE′) and the associated radius of curvature of the concave mirror is twice the size of the radius of curvature of the second intermediate image Zb 2 . As a result, firstly, there is a perfect, plane image of the first conjugate pupil PE′ (at the identical distance R) in the second conjugate pupil PE″, independently of the respective field angle, and, secondly, the rays in the second conjugate pupil PE″ are collimated in such a way that plane wavefronts are present there. As a result, handling the rays in the further course of the detection beam path is simple. In alternative embodiments (not depicted here), the radii of curvature of concave mirror and second intermediate image may deviate from one another such that non-planar wavefronts are present in the second pupil PE″. 
         [0055]    Since the concave mirror  36  would image the first conjugate plane PE′ onto itself in the case of perpendicular light incidence, said concave mirror is tilted perpendicular to the plane in which the second beam deflection unit  30 B acts. As a result of the oblique incidence onto the concave mirror, the latter generates an astigmatism, which is compensated to the greatest possible extent by the toric form. For this purpose, the radius of curvature along the y-axis is reduced in relation to the radius of curvature of the second intermediate image Zb 2  by the factor cos (angle of incidence) and the radius of curvature along the x-axis is increased in relation to the radius of curvature of the second intermediate image Zb 2  by the same factor. 
         [0056]    Instead of the second beam deflection unit  30 B, a wavefront modulator  30 B may be arranged in the second conjugate pupil plane PE″ or, preferably, in a third conjugate pupil plane (not depicted here). 
         [0057]    As an alternative to the toric form, the concave mirror  36  may have a spherical form, in which the first center of curvature and second center of curvature are identical. Then, a cylindrical optics  41 , for example in the form of a weak cylindrical lens, may be arranged on the side of the concave mirror  36  distant from the scan optics  35  for the purposes of compensating the astigmatism resulting from the oblique incidence on the concave mirror  36 . Preferably, the cylindrical optics  41  may be arranged on the side of the second beam deflection unit  30 B distant from the scan optics  35 , i.e. in the so-called “de-scanned” beam path section. The cylindrical optics  41  may be dispensed with in the case of a toric concave mirror  36 . 
         [0058]    If the first beam deflection unit is two-dimensional, i.e. adjustable for deflection in the x-direction and y-direction, the collimation optics may be e.g. a simple lens. 
         [0059]    Finally,  FIG. 5  shows an alternative transfer optics. The beams are collimated like in the prior art in the region of the beam deflection unit  30 , which is arranged in a conjugate pupil plane PE′. The scan optics  35  and the converging optics  37  disposed downstream of the beam deflection unit  30  form a finite relay optics, which images the first intermediate image Zb 1  into the second intermediate image Zb 2 . A collimation optics  36  is arranged in the further course such that e.g. collimated beams are present at the principal beam splitter  33 . In other embodiments (not depicted here), a plurality of principal beam splitters may, for example, only follow after a further converging optics. 
         [0060]    The scan optics  35  and the converging optics  37  are axially displaceable for adapting to the pupil shift when changing or displacing the microscope objective  21 . The displacement of both optics  35 ,  37  is performable by means of a control unit, for example always in the same sense and over the same distance, optionally also in a synchronous manner. 
         [0061]    The described arrangement of the beam deflection unit in a non-collimated beam path section may be used for further applications, for example for optical manipulation of the sample or for deflection of beams which are generated by means of a beam shaping optics, for example a spatial light modulator (SLM), for example Bessel beams or Mathieu beams. 
         [0062]    In alternative embodiments (not depicted here), the object-side focus may have a form deviating from that of a point. By way of example, it may have the form of a line. 
         [0063]    While this invention has been described in conjunction with the specific embodiments outlined above, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art. Accordingly, the preferred embodiments of the invention as set forth above are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the inventions as defined in the following claims. 
       LIST OF REFERENCE SIGNS 
       [0000]    
       
           10  Light-scanning microscope 
           20  Coupling optics 
           21  Microscope objective 
           22  Fiber optical waveguide 
           23  Laser 
           24  Light door 
           25  Attenuator 
           26  Fiber coupler 
           27  Tube lens 
           28  Filter 
           29  Color splitter 
           30  Beam deflection unit 
           31  Stop 
           32  Photomultiplier 
           33  Principal beam splitter 
           34  Control unit 
           35  Scan optics 
           36  Collimation optics 
           37  Converging optics 
           38  Detection optics 
           39  NLO beam splitter 
           40  NLO detector 
           41  Cylindrical optics 
         D Detection module 
         L Illumination module 
         M Microscope unit 
         N NLO detection module 
         P Sample 
         PE(′/″) (Conjugate) pupil plane 
         R Distance 
         S Scan module 
         V Virtual object 
         Zb 1 / 2  Intermediate image plane