Beam Splitting Device

Abstract

The beam splitting device (202, 402, 502) for separating the illumination light (204) and the detection light (206) in the optical apparatus (200) includes a light supply unit (208) configured to supply the illumination light (204) including a first illumination light (212) having a wavelength within a first wavelength range and a second illumination light (214) having a wavelength within a second wavelength range, with the first wavelength range and the second wavelength range separated from each other; The optical system includes an acousto-optical component (216) that is adjustable to diffract at least one spectral component of the bright light (212) to generate at least one illumination light beam (234) of a predetermined diffraction order while transmitting second illumination light (214) within a second wavelength range without diffraction, and a light combining unit (218, 418, 518) configured to couple the first illumination light (212) and the second illumination light (214) from the light providing unit (208) into the acousto-optical component (216). The light providing unit (208) is configured to provide the first illumination light (212) and the second illumination light (214) collinearly to the light combining unit (218, 418, 518). The optical combining unit (218, 418, 518) is configured to spatially separate the first illumination light (212) and the second illumination light (214) and direct the first illumination light (212) and the second illumination light (214) to the acousto-optical component (216) along different optical propagation directions.

Description

[Technical field]

[0001] The present invention relates to a beam splitting device for separating illumination light and detection light in an optical apparatus, and further to an optical apparatus comprising a beam splitting device. [Background technology]

[0002] In the field of microscopy, it is often necessary to separate illumination and detection light, each having different wavelengths and propagating along a common optical path. For example, in fluorescence applications, it may be desirable to filter out certain color bands of both the excitation and fluorescence emissions. For this purpose, beam splitting devices based on dichroic optics, colored filters and mirrors can be used. A wide variety of such optical elements are available, but they are limited in terms of flexibility in wavelength selection.

[0003] Recently, acousto-optical components have been used as beam splitters, as disclosed in EP 1055144, EP 1281997 and EP 1421427. Such acousto-optical components can be made of materials such as glass or quartz or crystalline materials. For example, the material can be tellurium dioxide TeO. 2 The acousto-optical component may consist of a piezoelectric transducer that is electrically controllable to generate sound waves in the material, which can be thought of as a periodically moving surface that expands and contracts to change the refractive index. Light incident on the crystal is diffracted by the resulting periodic index modulation, resulting in interference similar to Bragg diffraction. Thus, the acousto-optical component can be arbitrarily tuned to diffract one or more components of light incident on the crystal, where the diffracted light components exit the crystal in a direction different from the propagation direction of the undiffracted light. This allows for convenient spatial separation of the light.

[0004] However, typical acousto-optical components are limited in terms of their spectral width, i.e. in terms of the range of wavelengths of light that can be processed by the acousto-optical components. Currently, the spectral width of acousto-optical components typically covers a range of less than an octave, for example, a range of about 440 nm to 800 nm. If light outside of this standard range is not required, the entire light can be fed into the acousto-optical component through a single port. However, extending the wavelength beyond the standard range is technically very difficult to achieve. Therefore, if additional light with a wavelength outside the standard range is required, this additional light must be coupled into the system through a second port that bypasses the acousto-optical component. Using more than one port to feed the entire light into the system has the disadvantage that the different light components must be spatially aligned with each other with respect to their respective light propagation directions. Summary of the Invention [Problem to be solved by the invention]

[0005] SUMMARY OF THE DISCLOSURE It is an object of the present invention to provide a beam splitting device which allows for the separation of illumination light and detection light in an optical system in a reliable and compact manner. [Means for solving the problem]

[0006] The above mentioned object is achieved by the subject matter of claim 1. Advantageous embodiments are defined in the respective dependent claims and in the following description.

[0007] The beam splitting device for separating the illumination light and the detection light in the optical apparatus comprises a light supplying unit configured to supply illumination light including a first illumination light having a wavelength within a first wavelength range and a second illumination light having a wavelength within a second wavelength range, with the first and second wavelength ranges separated from each other. The beam splitting device further comprises an acousto-optical component that is adjustable to diffract at least one spectral component of the first illumination light having a selected wavelength within the first wavelength range to generate at least one illumination light beam of a predetermined diffraction order, while transmitting the second illumination light within the second wavelength range without diffraction. The beam splitting device further comprises a light combining unit configured to couple the first and second illumination lights from the light supplying unit into the acousto-optical component. The light supplying unit is configured to supply the first and second illumination lights to the light combining unit collinearly. The light combining unit is configured to spatially separate the first illumination light and the second illumination light and direct the spatially separated first illumination light and second illumination light along different light propagation directions to the acousto-optical component.

[0008] The beam splitting device allows the entire light, including the first and second illumination light, to be introduced through a single port into the illumination light path leading to the sample to be imaged. For this purpose, the entire illumination light is guided through an acousto-optical component, which is controlled to diffract only the first illumination light while leaving the second illumination light undiffracted. The light combining unit serves to couple the first and second illumination lights along different propagation paths into the acousto-optical component, where each propagation path is selected such that the first and second illumination lights emerging from the acousto-optical component are combined as desired to illuminate the sample together.

[0009] Thus, in contrast to conventional approaches using spatially separated ports, e.g. optical fibers each introducing different spectral components into the illumination path, the beam splitting device proposed herein allows the first and second illumination light to be guided through the same optical component. This ensures that adverse effects due to drift or misalignment caused by thermal expansion are avoided. In particular, lateral deviations between the focal points of the illumination light originating from one port and the other port are prevented. Instabilities and color-dependent offsets of the focal points between the respective illumination foci are thus avoided.

[0010] In addition, compared to conventional approaches, by providing only one port for coupling illumination light into the system, fewer optical components, mounting and adjustment elements are required in the illumination path up to the point where the illumination light is coupled in, such as optical fibers, lenses, mirrors, etc. Thus, the cost of implementing the proposed configuration is relatively low.

[0011] The spatial separation of the first illumination light and the second illumination light caused by the light combining unit does not have to be strictly understood as the first wavelength range and the second wavelength range must be completely separated from each other, i.e. only the light of the first wavelength range propagates along the first direction to the acousto-optical component and only the light of the second wavelength range propagates along the second direction to the acousto-optical component. Although such a complete light separation may be desirable, from a practical point of view, it may be sufficient if the light combining unit is configured to spatially separate the first illumination light and the second illumination light at least to a major extent from each other. Thus, for example, if the light combining unit uses dichroic elements that provide light separation by reflecting and transmitting different spectral components, it may not be possible to achieve a complete separation, especially if the spectral components to be separated from each other are spectrally close. For example, a major extent of separation is feasible if the light combining unit can separate the first illumination light and the second illumination light to a degree of more than 50%, preferably to a degree of more than 70%, and even better to a degree of more than 90%. In this case, less than 50%, less than 30% or less than 10% of the intensity of each illumination light is separated into a false channel, i.e., actually propagates to the acousto-optical component along the direction intended for the other illumination light. Solely for the sake of simplicity, perfect separation will be assumed in the following description, keeping in mind that the first and second illumination lights need only be separated to a major or major extent.

[0012] The light supply unit is a component that introduces illumination light into the illumination light path of the optical device. For this purpose, the supply unit can comprise one or more optical fibers and / or one or more light sources, in particular a laser source that emits illumination light into the fiber. The laser source can be coupled to a module contained in the supply unit. Furthermore, a so-called white light laser (supercontinuum laser) source that emits laser light with a continuous spectrum may be included in the supply unit. Apart from the above-mentioned components, the supply unit may also comprise other types of further elements, such as one or more optical filters, a scanner, etc.

[0013] Although not intended to be limiting, beam splitting devices may be advantageously used in microscopes, particularly laser scanning microscopes, where illumination light is shone onto a sample to excite fluorescence which is then detected to image the sample.

[0014] In a preferred embodiment, the light supply unit includes a single optical fiber configured to emit the first illumination light and the second illumination light collinearly toward the light combining unit, the optical fiber may be a single mode fiber, and the optical output end thereof can be effectively used as a single point light source.

[0015] Preferably, the acousto-optical component is configured to transmit the detection light without diffraction, in which case the acousto-optical component can be used as a passive element with respect to the second illumination light and the detection light, i.e. as an actively non-controlled element that only affects the light by refraction and not by diffraction.

[0016] The light combining unit may include an optical element configured to reflect the first and second illumination lights along different propagation directions to the acousto-optical component, for example, the optical element may be formed by a prism having a suitable geometry to allow different incidence directions of the first and second illumination lights to the acousto-optical component.

[0017] In a particular embodiment, the light combining unit may have a front surface facing the light supply unit and a rear surface facing away from the supply unit. The front surface includes a first front portion having a dichroic layer configured to reflect one of the first light and the second light toward the acousto-optical component and transmit the other of the first light and the second light toward the rear surface by refraction. The rear surface may include a first rear surface portion configured to reflect the other of the first light and the second light back toward the front surface. The front surface may include a second front surface portion spatially separated from the first front surface portion and configured to transmit the other of the first light and the second light reflected back from the first rear surface portion toward the acousto-optical component by refraction. The first rear surface portion may be non-parallel to at least one of the first front surface portion and the second front surface portion.

[0018] By using the non-parallel surface portions of the front and rear surfaces of the light-coupling unit, the design of the light-coupling unit can be easily and accurately adjusted to different incident directions of the first illumination light and the second illumination light to the acousto-optical component, and the difference in the two illumination directions is mainly caused by the manufacturing precision of the light-coupling unit.

[0019] It should be noted that the dichroic layer need not be limited to the first front portion, rather, the dichroic layer may cover the entire front surface of the light combining unit to simplify manufacturing.

[0020] Preferably, the first rear surface portion includes a reflective coating, such as a metallic or dielectric coating, configured to reflect the other of the first and second light back to the second front surface portion, the dielectric or metallic coating being suitable for reflecting the respective light back to the front surface of the light-combining unit and at the same time usable to adjust the polarization state of the reflected light, if required.

[0021] The front surface, including the first front portion and the second front portion, may be formed by a single flat surface, where the first rear portion is non-parallel to the flat front surface, and the inclination angle of the rear portion relative to the flat front surface may be precisely selected depending on the desired difference between the directions in which the first and second illumination light propagate towards the acousto-optical component.

[0022] According to another embodiment, the rear surface including the first rear surface portion is formed by a single flat surface, where one of the first front surface portion and the second front surface portion is non-parallel to the flat rear surface, while the other of the first front surface portion and the second front surface portion is parallel to the flat rear surface. This embodiment also allows the intended difference between the directions in which the first and second illumination lights propagate towards the acousto-optical component to be precisely adjusted. Again, the difference in the two illumination directions is mainly caused by the manufacturing precision of the light combining unit.

[0023] The rear surface may include a second rear surface portion parallel to one of the first front surface portion and the second front surface portion.

[0024] According to a preferred embodiment, the optical element is configured to transmit the detection light through the parallel front and rear surface portions of the optical element, and since the detection light passes through the parallel surface portions of the light coupling unit, the light coupling unit only causes a translational movement of the detection light, which makes it easy to configure the light detection path.

[0025] Preferably, the light combining unit and the acousto-optical component are adapted to one another in such a way that the at least one diffracted illumination light beam of the first illumination light and the second illumination light transmitted without diffraction are emitted collinearly or at least parallel from the acousto-optical component, in particular if the emitted light components are combined collinearly, any defocusing of the illumination light in the sample can be avoided.

[0026] In a preferred embodiment, the beam splitting device comprises optical means configured to change the polarization state of at least one of the first and second illumination lights so that at least one diffracted illumination light beam of the first illumination light and the second illumination light leave the acousto-optical component with the same polarization state. The aforementioned means for changing the polarization state may comprise, for example, a reflective coating applied to the rear surface of the light combining unit. Alternatively, a wave plate may be used that rotates the polarization direction of one of the first and second illumination lights by a predetermined amount, for example 90°, with respect to the other illumination light. The wave plate may be located upstream of the position where the first and second illumination lights enter a common optical fiber and emit light towards the light combining unit.

[0027] The light-combining unit and the acousto-optical component may be adapted to each other to compensate for dispersion. Illumination light propagating between the front and rear faces of the light-combining unit is scattered. Therefore, when the illumination light is incident from the light-combining unit towards the acousto-optical component, a wavelength-dependent angular division of the illumination light may occur. On the other hand, the acousto-optical component may also cause dispersion and thus an angular division of the light. This can be taken into account when selecting a suitable material for the light-combining unit to compensate for the unfavorable dispersion effect.

[0028] The beam splitting device may have an additional acousto-optical component that transmits the detection light towards the detector, the additional acousto-optical component being configured to compensate for the prism effect caused by the acousto-optical component. The additional acousto-optical component may be structurally identical to the other acousto-optical components and may be oriented in the opposite direction to these other acousto-optical components. The additional acousto-optical component may form a passive element in terms of diffraction. However, the additional acousto-optical component may also be used as a second active element to further or additionally suppress certain wavelengths or polarization components.

[0029] According to another aspect, there is provided an optical apparatus comprising the beam splitting device disclosed herein. The optical apparatus may be a microscope, in particular a laser scanning microscope.

[0030] In the following, specific embodiments will be described with reference to the drawings. [Brief description of the drawings]

[0031] [Figure 1] 1 is a schematic diagram of a laser scanning microscope including a beam splitting device according to a comparative example. [Diagram 2] FIG. 1 is a schematic diagram illustrating a laser scanning microscope including a beam splitting device according to one embodiment. [Diagram 3] 3 is a schematic diagram showing the laser scanning microscope of FIG. 2 based on different views of the light path provided by the beam splitting device. [Figure 4] FIG. 1 is a schematic diagram illustrating a laser scanning microscope including a beam splitting device according to another embodiment. [Diagram 5] FIG. 1 is a schematic diagram illustrating a laser scanning microscope including a beam splitting device according to another embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] A comparative example is first described to illustrate a conventional arrangement for separating illumination light and detection light in an optical device with reference to Fig. 1. Then, specific embodiments are described with reference to Figs. 2 to 5, which show the differences of the technical solution proposed in this specification compared to the conventional arrangement.

[0033] It should be noted that Figures 1-5 are used only to illustrate features that may aid in understanding the mode of operation in the context of the present disclosure. Of course, the particular configurations shown in Figures 1-5 may include additional components that are not shown in Figures 1-5. In particular, Figures 1-5 show a microscope as an example. It is clear that the microscope herein, when used in practice, includes additional elements such as lenses, filters, light sources, and the like.

[0034] FIG. 1 illustrates a conventional laser scanning microscope 100 as an example of an optical apparatus that uses a conventional beam splitting device 102 to separate illumination light irradiated onto a sample (not shown in FIG. 1) from detection light emitted from the sample.

[0035] The comparative beam splitting device 102 includes a light supply unit formed by two optical fibers 104 and 106. The first optical fiber 104 is used to supply a first illumination light 108 to an illumination light path of the laser scanning microscope 100 through a lens 110. By way of example only, it may be assumed that the first illumination light 108 has a wavelength within a first wavelength range of approximately 440 nm to 800 nm. Here, the direction in which the first illumination light 108 propagates through the laser scanning microscope 100 is indicated by a dashed-dotted arrow. The second optical fiber 106 is used to supply a second illumination light 112 to the light illumination path through a lens 114. In this example, it may be assumed that the second illumination light 112 has a wavelength within a second wavelength range of approximately 400 nm to 410 nm. Here, the direction in which the second illumination light 112 propagates through the laser scanning microscope 100 is indicated by a dashed-dotted arrow.

[0036] The beam splitting device 102 comprises an acousto-optical component 116 formed by a crystal with a piezoelectric transducer (not shown in FIG. 1) that can be electrically adjusted to generate acoustic waves in the crystal acting as a diffraction grating. In this comparative example, it is assumed that the acousto-optical component 116 and its driving electronics are limited in terms of spectral width to a first wavelength range of 440 nm to 800 nm. The acousto-optical component 116 is thus configured to have an active effect by diffraction only on the first illumination light 108 and not on the second illumination light 112. The beam splitting device 102 is therefore designed to feed only the first illumination light 108 into the illumination path via the acousto-optical component 116, whereas the second illumination light 112 bypasses the acousto-optical component when introduced into the illumination path. In other words, the beam splitting device 102 shown in FIG. 1 couples a first illumination light 108 and a second illumination light 112 into an illumination path using two spatially separated ports represented by two optical fibers 104 and 106, where the port represented by optical fiber 106 bypasses the acousto-optical components.

[0037] Specifically, the first illumination light 108 emitted from the optical fiber 104 is reflected by the mirror 118 towards the acousto-optical component 116. The acousto-optical component 116 is configured to diffract spectral components of the first illumination light 108 to generate a first diffraction order illumination light beam 120 that exits the acousto-optical component 116 along an optical axis of an illumination path leading to the sample. The direction in which the first illumination light 108 reflected by the mirror 118 enters the acousto-optical component 116 is tilted such that the first diffraction order of the first illumination light 108 generated by the acousto-optical component 116 is deflected in line with, i.e., collinearly with, the optical axis O of the illumination path. After passing through the dichroic mirror 122, the illumination light beam 120 formed from the first diffraction order of the illumination light 108 propagates along the optical axis O towards the sample.

[0038] The second illumination light 112 emitted from the optical fiber 106 is reflected by the dichroic mirror 122 along the optical axis O, so that the second illumination light 112 is spatially combined with the first illumination light 108. As a result, the sample is illuminated with light composed of the light components formed by the first illumination light 108 and the second illumination light 112.

[0039] The beam splitting device 102 is further configured to guide the detection light 124 from the sample to a detector 126 of the laser scanning microscope 100 in a direction opposite to the propagation direction of the first illumination light 108 and the second illumination light 112 illuminating the sample. Here, the direction of propagation of the detection light 124 in the laser scanning microscope 100 is indicated by the dashed arrow in FIG. 1. The detection light 124 enters the acousto-optical component 116 through the dichroic mirror 122 and remains unaffected in terms of diffraction by the acousto-optical component 116 while passing through it. Thus, the detection light 124 leaves the acousto-optical component 116 without being diffracted by the acousto-optical component 116. After propagating through the mirror 118, the detection light 124 enters an additional acousto-optical component 128 provided to compensate for the prism effect caused by the acousto-optical component 116. For this purpose, the additional acousto-optical component 128 is structurally identical to the acousto-optical component 116, but is oriented in an opposite direction to the acousto-optical component 116. The additional acousto-optical component 128 thus forms a passive element in terms of diffraction, such that the detection light 124 passes through the acousto-optical component 128 towards the detector 126 without diffraction.

[0040] It should be noted that acousto-optical component 116 is shown in a highly simplified manner in Figure 1. In particular, acousto-optical component 116 will not typically have a parallelepiped shape as shown in Figure 1, with its light input and output faces shown as parallel faces. Rather, acousto-optical component 116 may be provided with light inlet and outlet faces that are inclined relative to one another.

[0041] In the comparative example shown in FIG. 1, the disadvantage must be considered that the first illumination light 108 and the second illumination light 112 are provided to the illumination path by two spatially separated ports represented by the optical fibers 104, 106. Thus, the spatially separated light coupling to the illumination path requires the first illumination light 108 and the second illumination light 112 to be guided through various optical components that may drift or misalign due to, for example, thermal expansion. Furthermore, there may be a lateral shift of the focus of the illumination light from one optical fiber relative to the other optical fiber. This may result in instability between the illumination foci and a color-dependent offset of the foci. In addition, providing two separate ports for coupling the illumination light into the system requires separate optical components, such as optical fibers, lenses, mirrors, mounting elements, and adjustment elements, to the point in the illumination path where the illumination light is coupled. Thus, the cost of implementing such an arrangement is high.

[0042] Below, specific embodiments are described that are suitable for overcoming the above-mentioned shortcomings.

[0043] In figures 2 and 3 a laser scanning microscope 200 is shown with a beam splitting device 202 used to separate the illumination light 204 directed to the sample (not shown in figures 2 and 3) and the detection light 206 emerging from the sample. Figures 2 and 3 show the same arrangement, differing only in the illustrated manner of light propagation. Figure 3 shows light in the form of beams, whereas in figure 2 only the main or central ray of each beam (corresponding to figure 1) is shown. The beam splitting device 202 of the laser scanning microscope 200 includes a light supply unit 208 which can be formed by a single optical fiber. The light supply unit 208 is arranged to supply the illumination light 204 through a lens 210 into the illumination light path of the laser scanning microscope. If the comparative example of FIG. 1 is adopted, it can be assumed that the illumination light 204 includes a first illumination light 212 having a wavelength within a first wavelength range of about 440 nm to 800 nm and a second illumination light 214 having a wavelength within a second wavelength range of about 400 nm to 410 nm. Thus, the first wavelength range and the second wavelength range are spectrally separated from each other. Needless to say, the above-mentioned wavelength ranges should be understood as merely examples. Furthermore, the spectral separation of the wavelength ranges is not limited to the case where the wavelength ranges are separated from each other by a spectral gap of 410 nm to 440 nm in this embodiment. Rather, the spectral separation of the wavelength ranges also includes the case where the first wavelength range and the second wavelength range are adjacent to each other without a gap, whereby the entire illumination light 204 including the first illumination light 212 and the second illumination light 214 is understood to represent a provideable continuous spectrum that can be emitted into the optical fiber 208 by, for example, a white light laser. 1, the directions of the first illumination light 212 and the second illumination light 214 propagating through the laser scanning microscope 200 are indicated by dashed and long dashed arrows, respectively. Similarly, the light propagation direction of the detection light 206 is indicated by a dashed arrow.

[0044] The beam splitting device 202 includes an acousto-optical component 216 that substantially corresponds to the comparative acousto-optical component 116 shown in FIG. 1. The acousto-optical component 216 may thus be formed by a crystal with an electrically adjustable piezoelectric transducer that generates acoustic waves in the crystal acting as an optical grating so that light is transmitted through the crystal. As in the comparative example, it is assumed that the acousto-optical component 216 and its driving electronics are limited in terms of spectral width to a first wavelength range of 440 nm to 800 nm. The acousto-optical component 216 is therefore only configured to actively tune wavelengths between 440 nm and 800 nm by diffraction. Wavelengths outside this range are not intended to be diffracted by the acousto-optical component 216.

[0045] Similarly, the acousto-optical component 216 is shown in a highly simplified manner, i.e., the acousto-optical component 116 does not typically have a parallelepiped shape in which the light input and output faces of the acousto-optical component 216 are shown as parallel faces, as shown in Figure 2. Rather, the acousto-optical component 216 may be provided with light entrance and exit faces that are inclined relative to one another.

[0046] The beam splitting device 202 includes a light combining unit 218 configured to couple the first illumination light 212 and the second illumination light 214 from a single optical fiber 208 into the acousto-optical component 216. The light combining unit 218 thus allows the entire illumination light 204 to be fed into the illumination path via one port represented by the optical fiber 208. In particular, the optical fiber 208 can be used to emit the first illumination light 212 and the second illumination light 214 collinearly towards the light combining unit 218. Thus, as will be explained in more detail below, the light combining unit 218 spatially separates the first illumination light 212 and the second illumination light 214 from each other and guides the first illumination light 212 and the second illumination light 214 to the acousto-optical component 216 along different optical propagation directions. Therefore, in contrast to the comparative example of FIG. 1, in which the second illumination light 112 bypasses the acousto-optical component 116, the embodiment shown in FIG. 2 allows not only the first illumination light 212 but also the second illumination light 214 to pass through the acousto-optical component 216.

[0047] The light combining unit 218 may include an optical element configured to reflect the first illumination light 212 and the second illumination light 214 along different propagation directions to the acousto-optical component 216. According to the embodiment shown in Fig. 2, the optical element may be a prism having a front surface 220 facing the light output end of the optical fiber 208 and a rear surface 222 facing away from the optical fiber 208. The front surface 220 includes a first front surface portion 224 and a second front surface portion 226 spatially separated from the first front surface portion 224. Similarly, the rear surface 222 includes a first rear surface portion 228 and a second rear surface portion 230 spatially separated from the first rear surface portion 228.

[0048] According to the embodiment shown in Fig. 2, the front surface 220 of the light-combining unit 218 is formed by a single flat surface. Thus, the first front surface portion 224 and the second front surface portion 226 are coplanar. In contrast, the first rear surface portion and the second rear surface portion are not coplanar, i.e. are inclined by an angle α relative to each other. Furthermore, the first rear surface portion 228 is oriented non-parallel to the flat front surface 220. In contrast, the second rear surface portion 230 is oriented parallel to the flat front surface 220.

[0049] The first front portion 224 may be provided with a dichroic layer 232 having spectral characteristics adapted to the wavelengths of light propagating through the laser scanning microscope 200. In particular, the dichroic layer 232 is configured to transmit the first illumination light 212 and the detection light 206 and to reflect the second illumination light 214. Thus, the first illumination light 212 is refracted by the dichroic layer 232 as it enters the light combining unit 218 towards the first rear portion 228.

[0050] The front surface 220 of the light combining unit 218 is oriented to reflect the second illumination light 214 toward the acousto-optical component 216. According to the configuration shown in Fig. 2 and Fig. 3, the surface normal of the front surface 220 is inclined with respect to the incident direction of the first illumination light 212 and the second illumination light 214 in the light combining unit 218. Therefore, the surface normal of the front surface 220 is also inclined with respect to the direction along which the second illumination light 214 is reflected by the front surface 220 toward the acousto-optical component 216. Furthermore, the first rear surface portion 228 is configured to reflect the first illumination light 212 refracted by the dichroic layer 232 back to the front surface 220, where the first illumination light 212 is deflected by refraction so as to exit the light combining unit 218 toward the acousto-optical component 216 along a propagation direction different from the propagation direction of the second illumination light 214 and enter the acousto-optical component 216. In particular, the propagation directions of the first illumination light 212 and the second illumination light 214 towards the acousto-optical component 216 are mutually inclined at an angle corresponding to the mutual inclination angle α of the first rear surface portion 228 and the second rear surface portion 230. To reflect the first illumination light 212 back to the front surface 220, the first rear surface portion 228 may be provided with a reflective coating 238, for example a metallic or dielectric coating.

[0051] The acousto-optical component 216 is adjustable by suitable driver electronics to diffract at least one spectral component of the first illumination light 212 having a selected wavelength to generate at least one illumination light beam 234 of a predetermined diffraction order, while transmitting the second illumination light 214 without diffraction. According to the embodiment shown in Figures 2 and 3, the acousto-optical component 216 is configured to diffract the first illumination light 212 in the first diffraction order. Furthermore, the light combining unit 218 and the acousto-optical component 216 are adapted to each other with respect to the light propagation direction in which the first illumination light 212 and the second illumination light 214 are deflected by the light combining unit 218 towards the acousto-optical component 216, so that the at least one illumination light beam 234 of the first illumination light 212 and the second illumination light 214 transmitted without diffraction are emitted from the acousto-optical component 216 collinearly or at least parallel. Therefore, the first illumination light 212 and the second illumination light 214 are combined by the acousto-optical component 216 to ensure that the illumination of the sample is performed using spatially coincident light in a wide wavelength range consisting of the first illumination light 212 and the second illumination light 214.

[0052] The acousto-optical component 216 is further configured to guide the detection light 206 from the sample in a direction opposite to the propagation direction of the first illumination light 212 and the second illumination light 214. Again, the direction in which the detection light 206 propagates in the laser scanning microscope 200 is indicated by the dashed arrow in FIG. 2. The detection light 206 remains unaffected by the acousto-optical component 216 as it passes through it. Thus, the detection light 206 leaves the acousto-optical component 216 without diffraction at the acousto-optical component 216. The detection light 206 passes through the light combining unit 218 while being laterally shifted by refraction at the front surface 220 and the second rear surface portion 230 parallel thereto. After passing through the light combining unit 218, the detection light 206 enters an additional acousto-optical component 236 provided to compensate for the prism effect caused by the acousto-optical component 216. 1, the additional acousto-optical component 236 is structurally identical to the acousto-optical component 216 and is oriented in an opposite direction to the acousto-optical component 216. The acousto-optical component 236 thus forms a passive element in terms of diffraction, such that the detected light 206 propagates without diffraction towards the detector (not shown in FIGS. 2 and 3).

[0053] The beam splitting device 202 may include optical means configured to change the polarization state of at least one of the first illumination light 212 and the second illumination light 214, so that the illumination light beam 234, i.e. the first order diffraction generated by the acousto-optical component 216 from the first illumination light and the second illumination light 214, exits the acousto-optical component 216 with equal polarization states. The aforementioned optical means for ensuring equal polarization states may include, for example, a reflective coating 238 applied to the first rear surface portion 228 of the light combining unit 218, which reflects the first illumination light 212 back to the front surface 220. The reflective coating 238 may be realized in such a way that no phase shift occurs upon reflection of the first illumination light 212. This may be achieved, for example, by having the reflective coating 238 include or consist of alternating thin dielectric layers each having a different refractive index (e.g., alternating low and high refractive index), where one of the layers is in contact with the glass body of the light-coupling unit 218 and exhibits a lower refractive index than that of the glass body of the light-coupling unit 218. During reflection at the interface, the light waves do not exhibit a phase shift. For this type of reflective coating 238, maximum reflectance of the illumination light 212 at a single wavelength may be achieved with each layer having a thickness of ¼ of the wavelength of the illumination light 212.

[0054] The above-mentioned implementations of the reflective coating 238 are merely examples. Other suitable implementations of the reflective coating 238 that reflect illumination light without a phase shift may, for example, include multiple layers having different refractive indices and thicknesses different from ¼ wavelength.

[0055] Considering such characteristics of the reflective coating 238, the illumination light 204 emitted from the optical fiber 208 can be linearly polarized, selected such that the polarization direction of the illumination light 204 is rotated by an angle of 45° with respect to the plane of incidence of the illumination light 204 on the front surface 220 of the light combining unit 218. Thus, the polarization direction of the second illumination light 214 reflected at the front surface 220 is rotated by an angle of 90°. As a result, the first illumination light 212 and the second illumination light 214 emitted from the light combining unit 218 have polarization directions rotated by 90° with respect to each other. The polarization direction of the first illumination light 212 is then rotated by 90° by the acousto-optical component 216 when diffracted into the first diffraction order. As a result, the illumination light beam 234 derived from the first illumination light 212 and the second illumination light 214 are emitted from the acousto-optical component 216 in the same polarization state.

[0056] Of course, the control of polarization in the above manner should be understood as merely exemplary. For example, rather than using a reflective coating 238 that does not introduce a phase shift, the polarization direction of the first illumination light 212 may be rotated 90° relative to the polarization direction of the second illumination light 214 before coupling the first illumination light 212 into the optical fiber 208. Such a rotation of the polarization direction can be achieved by a wave plate, taking into account that a polarization-maintaining optical fiber can typically transmit not only a specific polarization direction, but also a polarization direction rotated by 90°.

[0057] The tolerance range of the angle α, which determines the difference between the propagation directions of the first and second illumination lights to the acousto-optical component 216, can be selected so that the lateral deviation of the optical focus within the sample is less than twice the half-width of the point spread function (PSF), preferably less than one time the half-width of the PSF, and even better less than one-half the half-width of the PSF.

[0058] Furthermore, it can be considered that the first illumination light 212 is dispersed during propagation between the front surface 220 and the first rear surface portion 228 and after reflection between the first rear surface portion 228 and the front surface 220, resulting in a wavelength-dependent angular split for the first illumination light 212 emerging from the light combining unit 218. Thus, a wavelength-dependent lateral offset of the illumination focus in the sample occurs. Furthermore, the crystal of the acousto-optical component 216 generally also generates a wavelength-dependent angular split due to its dispersion, and thus also a wavelength-dependent lateral offset of the illumination focus. Thus, the light combining unit 218 and the acousto-optical component 216 can be adapted to each other so that the dispersion that would otherwise cause a lateral offset of the illumination focus is compensated. In particular, by selecting an appropriate material for the light combining unit 218, it is possible to achieve an angular split caused by the light combining unit 218 that is equal or at least approximately equal to an angular split caused by the acousto-optical component 216.

[0059] As a mere example, if we assume that the acousto-optical component 216 has an angular dispersion of 0.9 mrad between wavelengths of 490 nm and 800 nm, then for the first order diffraction, the optical coupling unit 218 is made of glass material N-PK51 manufactured by SCHOTT (Abbe number v d =76.98), the surface normal of the front surface 220 of the light combining unit 218 presents an angle of 45° with respect to the directions of incidence of the first and second illumination lights 212, 214, and the first and second rear surface portions 228, 230 are mutually inclined by an angle α of 2°, the same angular dispersion can be achieved.

[0060] In general, the acousto-optical components 216, 236 are preferably designed to have a small angular dispersion between 490 nm and 800 nm wavelengths for the first diffraction order, i.e. preferably less than 1.5 mrad, more preferably less than 1.0 mrad, most preferably less than 0.8 mrad. The glass material of the light-coupling unit 218 preferably has an Abbe number greater than 50, more preferably greater than 60, most preferably greater than 70.

[0061] The light combining unit 218 may be oriented such that the direction of the angular dispersion of the light combining unit 218 is opposite to the direction of the angular dispersion of the acousto-optical component 216. Thus, by appropriately positioning the light combining unit 218 relative to the acousto-optical component 216, compensation for the wavelength-dependent angular splitting may be achieved.

[0062] Figure 4 illustrates another embodiment of a beam splitting device 402 that may be included in the laser scanning microscope 200. The beam splitting device 402 of Figure 4 differs substantially from the embodiment illustrated in Figures 2 and 3 in that the light combining unit 418 has been modified.

[0063] The light-combining unit 418 shown in FIG. 4 includes a front surface 420 having a first front portion 424 and a second front portion 426. In contrast to the embodiment shown in FIG. 2 and FIG. 3, the first front portion 424 and the second front portion 426 are not coplanar. Rather, the first front portion 424 and the second front portion 426 are inclined by an angle β relative to each other. Furthermore, the light-combining unit 418 includes a rear surface 422 having a first rear portion 428 and a second rear portion 430. According to the embodiment shown in FIG. 4, the rear surface 422 having the first rear portion 428 and the second rear portion 430 is formed by a single flat surface that is parallel to the first front portion 424 and non-parallel to the second front portion 426.

[0064] The first front portion 424 is provided with a dichroic layer 432 that transmits both the first illumination light 212 and the detection light 206 and reflects the second illumination light 214. Thus, when the first illumination light 212 enters the light combining unit 418, it is refracted by the dichroic layer 432 towards the first rear portion 428.

[0065] The first front surface portion 424 of the light combining unit 418 is oriented to reflect the second illumination light 214 towards the acousto-optical component 216. The surface normal of the first front surface portion 424 is inclined with respect to the incident direction of the first illumination light 212 and the second illumination light 214 at the light combining unit 218. Therefore, the surface normal of the front surface 424 is also inclined with respect to the direction in which the second illumination light 214 is reflected by the front surface 424 towards the acousto-optical component 216.

[0066] The first rear portion 428 of the light combining unit 418 is configured to reflect the first illumination light 212 refracted by the dichroic layer 432 back to the second front portion 426 at an inclination angle β with respect to the first front portion 424. When passing through the second front portion 426, the first illumination light 212 is deflected by refraction, so that it exits from the light combining unit 418 towards the acousto-optical component 216 along a propagation direction different from the propagation direction of the second illumination light 214 entering the acousto-optical component 216. Similar to the embodiment shown in Figures 2 and 3, the propagation directions of the first illumination light 212 and the second illumination light 214 towards the acousto-optical component 216 deviate from each other according to the angle β at which the first front portion 424 and the second front portion 426 are mutually inclined. The first rear portion 428 may be provided with a reflective coating 438 , for example a metallic or dielectric coating, to reflect the first illumination light 212 towards the second front portion 426 .

[0067] 2 and 3, the acousto-optical component 216 of the beam splitting device 402 is adjustable to diffract at least one spectral component of the first illumination light 212 to generate the at least one illumination light beam 234, while transmitting the second illumination light 214 without diffraction. The light combining unit 418 and the acousto-optical component 216 are adapted to each other such that the at least one illumination light beam 234 of the first illumination light 212 and the second illumination light 214 are emitted from the acousto-optical component 216 collinearly or at least parallel (as shown in FIG. 4) to illuminate the sample.

[0068] Similar to the embodiment shown in Fig. 2 and Fig. 3, the acousto-optical component 216 of the beam splitting device 402 is configured to guide the detection light 206 from the sample in a direction opposite to the propagation direction of the first illumination light 212 and the second illumination light 214. The detection light 206 remains unaffected in terms of diffraction when passing through the acousto-optical component 216. Thus, the detection light 206 leaves the acousto-optical component 216 without diffraction. Thus, the detection light 206 passes through the light combining unit 418 while being laterally displaced by refraction at the first front surface portion 424 and the second rear surface portion 430. Since the first front surface portion 424 and the second rear surface portion 430 are parallel to each other, the light combining unit 418 only causes a translational movement of the detection light 206. After passing through an additional acousto-optical component 236 used to compensate for the prism effect, the detection light 206 is incident on a detector (not shown in Fig. 4).

[0069] Figure 5 shows another embodiment of a beam splitting device 502 that may be included in the laser scanning microscope 200. The configuration shown in Figure 5 differs substantially from the embodiment of Figures 2 to 4 in that the optical combining unit 518 used in the beam splitting device 502 has been modified.

[0070] The light-combining unit 518 includes a front surface 520 having a first front portion 524 and a second front portion 526. The first front portion 524 and the second front portion 526 are not coplanar, i.e., are inclined at an angle γ relative to each other. Additionally, the light-combining unit 518 shown in FIG. 5 has a rear surface 522 formed by a single flat surface that is parallel to the second front portion 526 and non-parallel to the first front portion 524.

[0071] The first front portion 524 of the light combining unit 518 is provided with a dichroic layer 532 that transmits the first illumination light 212 and reflects the second illumination light 214. The rear surface 522 of the light combining unit 518 may be provided with a reflective coating adapted to reflect the first illumination light 212 transmitted by the dichroic layer 532 back to the second front portion 526. Furthermore, the reflective coating applied to the rear surface 522 is adapted to transmit the detection light 206.

[0072] 2-4, the acousto-optical component 216 of the beam splitting device 502 is adjustable to diffract at least one spectral component of the first illumination light 212 to generate the at least one illumination light beam 234, while transmitting the second illumination light 214 without diffraction. The light combining unit 518 and the acousto-optical component 216 are adapted to each other such that the at least one illumination light beam 234 of the first illumination light 212 and the second illumination light 214 are emitted collinearly from the acousto-optical component 216 to illuminate the sample.

[0073] Similar to the above-described embodiment, the acousto-optical component 216 of the beam splitting device 502 is configured to guide the detection light 206 from the sample to a detector (not shown in FIG. 5 ) via the optical coupling unit 518. The detection light 206 remains unaffected by diffraction when passing through the acousto-optical component 216. However, the detection light 206 may be deflected due to refraction by the acousto-optical component 216, as shown in FIG. 5 . The detection light 206 may pass through the optical coupling unit 518 along a direction opposite to the propagation direction in which the first illumination light 212 is reflected at the rear surface 522 towards the second front portion 526 of the optical coupling unit 518. Thus, the detection light 206 and the first illumination light 212 are incident on the same position on the rear surface 522, which is coated with the above-mentioned reflective coating that reflects the first illumination light 212 and transmits the detection light 206. After passing through additional acousto-optical components 236 used to compensate for the prism effect, the detected light 206 is incident on the detector. As already mentioned above, the detected light 206 may pass through several additional components not shown in FIG. 5, such as lenses, mirrors, filters, pinholes, etc., before reaching the detector.

[0074] To ensure that the illumination light beam 234, i.e. the first order diffraction generated by the acousto-optical component 216, originates from the first illumination light and that the second illumination light 214 exits the acousto-optical component 216 with an equal polarization state, the polarization direction of the first illumination light 212 can be rotated by 90° with respect to the polarization direction of the second illumination light 214 before coupling the first illumination light 212 into the optical fiber 208. As already mentioned above, such a polarization direction rotation can be performed by a wave plate.

[0075] As used in this specification, the term "and / or" includes any and all combinations of one or more of the associated listed items and may be abbreviated as " / ".

[0076] Although some aspects have been described in the context of an apparatus, it will be apparent that these aspects also represent a description of a corresponding method, where a block or apparatus corresponds to a step or feature of a step, and similarly, aspects described in the context of a step also represent a description of a corresponding block or item or feature of a corresponding apparatus. [Explanation of symbols]

[0077] 100 Laser Scanning Microscope 102 Beam splitting device 104,106 Optical fiber 108,112 Illumination 116 Acousto-optical components 118 Mirror 120 Illumination Light Beam 122 Dichroic Mirror 124 Detection Light 126 Detector 128 Additional Acousto-Optical Components 200 Laser Scanning Microscope 202 Beam splitting device 204 Illumination 206 Detection Light 208 Light supply unit 210 Lens 212,214 Illumination 216 Acousto-optical components 218 Optical coupling unit 220 Front 222 Rear 224,226 Front part 228,230 Rear part 232 Dichroic Layer 234 Illumination Light Beam 238 Reflective Coating 402 Beam Splitting Device 418 Optical coupling unit 420 front 424,426 Front part 428,430 Rear part 432 Dichroic Layer 438 Reflective Coating 502 Beam Splitting Device 518 Optical Coupling Unit 520 front 522 Rear 524,526 Front part 532 Dichroic Layer O optical axis α, β, γ angles

Claims

1. A beam splitting device (202, 402, 502) configured to separate illumination light (204) irradiated onto a sample and detection light (206) emitted from the sample in an optical apparatus (200), the beam splitting device (202, 402, 502) comprising: a light supply unit (208) configured to supply illumination light (204) including a first illumination light (212) having a wavelength within a first wavelength range and a second illumination light (214) having a wavelength within a second wavelength range, the first wavelength range and the second wavelength range being separated from each other; an acousto-optical component (216) tunable to diffract at least one spectral component of a first illumination light (212) having a selected wavelength within the first wavelength range to produce at least one illumination light beam (234) of a predetermined diffraction order, while transmitting a second illumination light (214) within the second wavelength range without diffraction; a light coupling unit (218, 418, 518) configured to couple the first illumination light (212) and the second illumination light (214) from the light providing unit (208) into the acousto-optical component (216); Equipped with the light providing unit (208) is configured to provide the first illumination light (212) and the second illumination light (214) collinearly to the light combining unit (218, 418, 518); the light combining unit (218, 418, 518) is configured to spatially separate the first illumination light (212) and the second illumination light (214) and direct the spatially separated first illumination light (212) and the second illumination light (214) along different light propagation directions to the acousto-optical component (216); A beam splitting device (202, 402, 502).

2. the light supply unit includes a single optical fiber (208) configured to emit the first illumination light (212) and the second illumination light (214) collinearly toward the light combining unit (218, 418, 518); The beam splitting device (202, 402, 502) of claim 1.

3. the acousto-optical component (216) is configured to transmit the detection light (206) without diffraction; A beam splitting device (202, 402, 502) according to claim 1 or 2.

4. the light combining unit includes an optical element (218, 418, 518) configured to reflect the first illumination light (212) and the second illumination light (214) along different propagation directions to the acousto-optical component (216); A beam splitting device (202, 402, 502) according to any one of claims 1 to 3.

5. The light coupling unit (218, 418, 518) has a front surface (220, 420, 520) facing the light providing unit (208) and a rear surface (222, 422, 522) facing the opposite side to the light providing unit (208), the front surface (220, 420, 520) includes a first front surface portion (224, 424, 524) having a dichroic layer (232, 432, 532) configured to reflect one of the first illumination light (212) and the second illumination light (214) toward the acousto-optical component (216) and transmit the other of the first illumination light (212) and the second illumination light (214) toward the rear surface (222, 422, 522) by refraction; the rear surface (222, 422, 522) includes a first rear surface portion (228, 428) configured to reflect the other of the first illumination light (212) and the second illumination light (214) back to the front surface (220, 420, 520); the front surface (220, 420, 520) includes a second front surface portion (226, 426, 526) that is spatially separated from the first front surface portion (224, 424, 524) and configured to transmit the other of the first illumination light (212) and the second illumination light (214) reflected back from the first rear surface portion (228, 428) toward the acousto-optical component (216) by refraction; the first rear surface portion (228, 428) is non-parallel to at least one of the first front surface portion (224, 424, 524) and the second front surface portion (226, 426, 526); A beam splitting device (202, 402, 502) according to any one of claims 1 to 4.

6. the first rear surface portion (228, 428) includes a reflective coating (238, 438) configured to reflect the other of the first illumination light (212) and the second illumination light (214) back to the second front surface portion (226, 426); The beam splitting device (202, 402) of claim 5.

7. the front surface (220), including the first front portion (224) and the second front portion (226), is formed by a single planar surface; the first rear surface portion (228) is non-parallel to the planar front surface; A beam splitting device (202) according to claim 5 or 6.

8. the rear surface (422, 522) including the first rear surface portion (428) is formed by a single flat surface; one of the first front portion (424, 524) and the second front portion (426, 526) is non-parallel to the planar rear surface, while the other of the first front portion (424, 524) and the second front portion (426, 526) is parallel to the planar rear surface; A beam splitting device (402, 502) according to claim 5 or 6.

9. the rear surface (222, 422, 522) includes a second rear surface portion (230, 430) parallel to one of the first front surface portion (224, 424, 524) and the second front surface portion (226, 426, 526); A beam splitting device (202, 402, 502) according to any one of claims 5 to 8.

10. The light coupling unit (218, 418, 518) has a front surface (220, 420, 520) facing the light supply unit (208) and a rear surface (222, 422, 522) facing the opposite side to the light supply unit (208), The optical element (218, 418, 518) is configured to transmit the detection light (206) through each surface portion of the front surface (220, 420, 520) and the rear surface (222, 422, 522) that are parallel to each other. The beam splitting device (202, 402, 502) of claim 4.

11. the light combining unit (218, 418, 518) and the acousto-optical component (216) are adapted to each other such that at least one diffracted illumination light beam (234) of the first illumination light (212) and the second illumination light (214) transmitted without diffraction are emitted from the acousto-optical component (216) collinearly or at least parallel. A beam splitting device (202, 402, 502) according to any one of the preceding claims.

12. the beam splitting device (202, 402) includes optical means (238, 438) configured to change the polarization state of at least one of the first illumination light (212) and the second illumination light (214) such that at least one diffracted illumination light beam (234) of the first illumination light (212) and the second illumination light (214) exit the acousto-optical component (216) with the same polarization state; A beam splitting device (202, 402) according to any one of claims 1 to 11.

13. the optical combining unit (218, 418, 518) and the acousto-optical component (216) are adapted to each other to compensate for dispersion; A beam splitting device (202, 402, 502) according to any one of claims 1 to 12.

14. the beam splitting device (202, 402, 502) includes an additional acousto-optical component (236) that transmits the detection light (206) toward a detector (126), the additional acousto-optical component (236) being configured to compensate for a prism effect caused by the acousto-optical component (216); A beam splitting device (202, 402, 502) according to any one of claims 1 to 13.

15. An optical arrangement (200) comprising a beam splitting device (202, 402, 502) according to any one of claims 1 to 14.

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