Solid-state spatial heterodyne spectrometer

Abstract

A spatial heterodyne spectrometer for spectrally analyzing incoming light in a spectral analyzation range comprises a spectrometer beam splitter (38), a first diffractive grating (40a), with a first arm (42a) of the spectrometer extending between the spectrometer beam splitter (38) and the first diffractive grating (40a), and a second diffractive grating (40b), with a second arm (42b) of the spectrometer extending between the spectrometer beam splitter (38) and the second diffractive grating (40b). The spectrometer beam splitter (38) splits the incoming light along a first axial direction (56a) into the first arm (42a) and along a second axial direction (56b) into the second arm (42b). Each arm (42a, 42b) comprises a solid, transparent body (48a, 48b) that is transparent over the spectral analyzation range and extends all the way from the spectrometer beam splitter (38) to the grating (40a, 40b). Each transparent body (48a, 48b) includes a first body section (50a, 50b) with a first refractive index and a second body section (52a, 52b) with a second, different refractive index. The second body sections (50a, 50b; 52a, 52b) are adjacent to each other and form a planar refractive interface (54a, 54b) between them, which is tilted in respect to the axial direction (56a, 56b). In each arm (42a, 42b), the grating (40a, 40b) is arranged adjacent to and along a distal surface of the transparent body (48a, 48b).

Description

[0001] Solid-state spatial heterodyne spectrometer

[0002] Technical Field

[0003] The invention relates to a spatial heterodyne spectrometer for spectrally analyzing incoming light in a spectral analyzation range.

[0004] Background Art

[0005] Spectrometers for spatial heterodyne spectrometry (SHS), such as, e.g., described in US10908023, comprise a beam splitter dividing the incoming light along two arms of an interferometer. At the end of each arm, the light is reflected by means of a tilted diffractive grating. Each spectral component of the light returns to the beam splitter, where it is overlapped with its counterpart from the other arm.

[0006] The pairs of diffracted spectral components generate interference patterns having different spatial frequencies. These interference patterns can be detected by a camera, and the one- or two-dimensional camera image can be subject to spectral analysis in order to detect the amplitudes of the different spatial frequencies and, thereby, the amplitudes of the diffracted spectral components.

[0007] As described in US10908023, each arm may comprise a field widening prisms to increase the overlap of the pairs of diffracted spectral components at the location of the camera located at the exit side of the beam splitter, and spacers may be used to hold the gratings at a distance from and at a suitable angle in respect to a remote surface of the prisms.

[0008] Disclosure of the Invention

[0009] The problem to be solved by the present invention is to provide a robust and compact type of such an SHS spectrometer.

[0010] This problem is solved by the spatial heterodyne spectrometer of claim 1.

[0011] Accordingly, the spatial heterodyne spectrometer for spectrally analyzing incoming light in a spectral analyzation range comprises at least the following elements: - A spectrometer beam splitter: The beam splitter may be used to split an incoming light beam to be analyzed into a first and a second part.

[0012] - A first diffractive grating. A first arm of the spectrometer extends between the beam splitter and the first diffractive grating.

[0013] - A second diffractive grating. A second arm of the spectrometer extends between the beam splitter and the second diffractive grating.

[0014] The spectrometer beam splitter is adapted to split the incoming light along a first axial direction into the first arm and along a second axial direction into the second arm.

[0015] Each arm comprises a solid, transparent body that is transparent over the spectral analyzation range and that extends from the spectrometer beam splitter to the grating.

[0016] Each transparent body comprises a first body section having a first refractive index and a second body section having a second refractive index different from the first refractive index. The first and the second body sections are adjacent to each other and form a planar refractive interface between them. The refractive interface tilted in respect to the axial direction of its arm in the sense that the angle between the normal vector of the refractive interface and the axial direction is larger than 0° and smaller than 90°. For example, the angle may be between 5° and 45°.

[0017] Further, in each arm, the grating is arranged adjacent to and along the distal surface of the transparent body.

[0018] This design is based on the understanding that a more compact and robust device can be created by replacing the prior art field widening prisms and spacers by a solid transparent body extending all the way from the beam splitter to the grating, with the tilted refractive interface taking over the role of the field widening prism, and the grating being directly arranged on the distal surface of the transparent body.

[0019] In an even more compact and robust design, the grating of each arm may be a surface grating at the distal side of the transparent body. This obviates the need for providing a separate grating element. It may also reduce undesired additional reflections at interfaces between different components.

[0020] Brief Description of the Drawings

[0021] The invention will be better understood and objects other than those set forth above will become apparent when consideration is given to the following de- tailed description thereof. Such description makes reference to the annexed drawings, wherein:

[0022] Fig. 1 shows a sectional view of an embodiment of a spectrometry device including an SHS spectrometer,

[0023] Fig. 2 shows a first class of embodiments of a spectrometer beam splitter and its arms,

[0024] Fig. 3 shows a second class of embodiments of a spectrometer beam splitter and its arms,

[0025] Fig. 4 shows a third class of embodiments of a spectrometer beam splitter and its arms,

[0026] Fig. 5 shows a first embodiment of a grating arranged at the remote side of the transparent body, and

[0027] Fig. 6 shows a second embodiment of a grating arranged at the remote side of the transparent body.

[0028] Modes for Carrying Out the Invention

[0029] Definitions

[0030] The term "transversal" is to be understood as "non-parallel".

[0031] A plane is "tilted" in respect to a direction if the plane is neither parallel nor perpendicular to the direction.

[0032] In the arms of the SHS spectrometer, "proximal" designates a side or direction facing the beam splitter and "distal" designates a side or direction facing away from the beam splitter.

[0033] The term "adjacent" is understood to indicate that there is no gap between two parts. In most examples, the distance between the two parts is smaller than one micrometer, i.e., in the order of the wavelength of the spectral analyzation range or less.

[0034] Example Design

[0035] Fig. 1 illustrates the design of some embodiments of a device with a spectrometer, such as it can, e.g., be used for Raman spectroscopy or other types of spectroscopy.

[0036] The shown device may comprise functional sections including an illumination and receiver section 2, a collimator 4, and a spectrometer 6. Illumination and receiver section 2 is adapted to send light at an excitation wavelength range onto a target 8 and to receive returning light scattered from target 8. The scattered light may, e.g., include Raman-scattered light, fluorescent light, or other light the spectral properties of which are to be analyzed.

[0037] Collimator 4 is adapted to collimate the returning light, preparing it for entry into spectrometer 6.

[0038] Spectrometer 6 is adapted to spectrally analyze the light from collimator 4.

[0039] The device may further comprise a support structure 10 holding the various elements in place.

[0040] It must be noted that other means than illumination and receiver section 2 and / or collimator 4 may be provided to feed a substantially collimated light field to spectrometer 6. For example, the light to be analyzed may come from an optical fiber with a collimation lens or from a measurement chamber analyzing a sample with collimated light in transmission.

[0041] However, a compact Raman spectrometry device of the type shown in Fig. 1 is one of the applications of the present spectrometer because the spectrometer is well-suited for compact, robust apparatus that may, e.g., be integrated in wearable devices, such as a smartwatch.

[0042] Hence, the components of such a spectrometry device of Fig. 1 are described in the following in more detail.

[0043] Illumination and receiver Section

[0044] The shown illumination and receiver section 2 comprises a light source 20 emitting light at an excitation wavelength range.

[0045] The excitation wavelength range is centered around a center excitation wavelength Ao and has a full-width-half-maximum range AA.

[0046] For Raman spectroscopy, AX may be small for good resolution, such as smaller than 5 nm or even smaller than 1 nm.

[0047] Ao depends on the application.

[0048] For glucose detection, for example, o may be between 780 and 790 nm, such as 785 nm, with a corresponding spectral analyzation range between 800 nm and 950 nm (corresponding to a Stokes shift of about 239 to 2213 cm ').

[0049] In another example, Ao may be between 825 and 835 nm, such as 830 nm, where cost-effective lasers are available and less parasitic fluorescence may be generated), and the spectral analyzation range may be between 845 nm and 960 nm (corresponding to a Stokes shift of about 214 to 1415 cm '). Other values of o may, e.g., be 795, 808, 830, or 850 nm because lasers are, e.g., available for these wavelengths.

[0050] A typical range of o may be between 750 and 880 nm.

[0051] In other examples, Ao may be in the UV for detecting resonance effects of proteins, or Ao may be around 1065 nm, again for reducing fluorescence, or it may be around 720 nm for resonance with hemoglobin.

[0052] Light source 20 may, e.g., be a vertical -cavity surface-emitting laser (VCSEL) for its compact size, narrow bandwidth, mass-production capabilities, and large light power.

[0053] Illumination section 2 further comprises illumination optics 22a - 22d, which is adapted to project light from light source 20 through a sensing port 24 towards target 8 in order to generate Raman scattered light in the target.

[0054] Note that the number of lenses in the illumination optics 28a - 28d depends on implementation and may differ from four. For example, only a single lens may be used before and / or after the beam splitter.

[0055] In the shown type of embodiments, part of illumination optics 22a - 22d (namely the lenses 22c, 22d in the shown embodiment) process both the light from light source 20 on its way to target 8 as well as the scattered light returning from target 8. Therefore, illumination section 2 may comprise a dichroic beam splitter 26 for separating light in the excitation wavelength range from the returning Raman- scattered light.

[0056] In the shown type of embodiments, dichroic beam splitter 26 passes light at the excitation wavelength range along the axis Ai of illumination section 2 while it reflects Raman-scattered light towards the collimation optics in collimator 4.

[0057] In alternative embodiments, though, dichroic beam splitter 32 may be adapted to reflect light at the excitation wavelength range while passing Raman- scattered light, in which case light source 20 and collimator 4 may be swapped in their positions.

[0058] In yet other embodiments, target 8 may, e.g., be illuminated from one direction while the Raman-scattered light is collected along another direction, in which case separate optics are used to project the excitation light towards the target and to receive the scattered returning light. In that case, dichroic beam splitter 26 may be dispensed with.

[0059] In yet other embodiments, the spectrometry device may not comprise an illumination section at all, and the light to be spectrally analyzed may be generated by other means. If a dichroic beam splitter 26 is used, as shown, a first part 22a, 22b of the illumination optics may be arranged on the path of the light between light source 20 and dichroic beam splitter 26, and a second part 22c, 22d of the illumination optics may be arranged on the path of the light between dichroic beam splitter 26 and sensing port 24. The first part 22a, 22b is adapted to collimate the light from light source 20 at dichroic beam splitter 26 while the second part 22c, 22d is adapted to focus the light from dichroic beam splitter 26 to a focal point at sensing port 24.

[0060] Collimator

[0061] Collimator 4 receives scattered light from illumination and receiver section 2 or from another source of radiation. In the shown embodiment, it comprises collimation optics 30a - 30c, with 30a, 30b being convex lenses and 30c being a pinhole. The distances between pinhole 30c and each lens 30a and 30b are equal to the focal lengths of the lenses 30a, 30b, respectively.

[0062] Collimation optics 30a - 30c is adapted to improve the collimation of the light scattered back from target 8 in order to send light of better collimation, along a collimation axis Ac, into spectrometer 6.

[0063] To do so, the already partially collimated light entering collimator section 4 is focused at pinhole 30c, which spatially filters out the poorly collimated light components, whereupon it is again collimated by lens 30b.

[0064] In a compact design, collimation axis Ac may extend transversally, in particular perpendicularly, to the illumination axis Ai of illumination and receiver section 2, with the illumination axis Ai being defined as extending from light source 20 to sensing port 24.

[0065] Spectrometer

[0066] Spectrometer 6 is adapted to analyze the spectrum of the light from collimator 4 within a spectral analyzation range. This range may, e.g., lie somewhere within Ao and Ao + 200 nm (with Ao being the center excitation wavelength as mentioned above) and have a spectral width of 50 and 150 nm. For example, if Ao = 785 nm, the spectral analyzation range may be from 800 nm to 950 nm.

[0067] In a typical example, the spectral analyzation range may be between 239 cm1and 2213

[0068] Spectrometer 6 is a spatial heterodyne spectrometer. Such spectrometers are, e.g., described by C.-A. Stbckling et al., " Optical Simulation and Design of Spatial Heterodyne Spectrometers for Remote Sensing Applications", EPJ Web of Conferences 238, 12018 (2020), For further references, see US5059027A or US10908023B2.

[0069] The spatial heterodyne spectrometer comprises a spectrometer beam splitter 38 and two gratings 40a, 40b. The spectrometer beam splitter 38 and the gratings 40a, 40b form a Michelson interferometer with two arms 42a, 42b.

[0070] The light from collimator section 4 enters through an entry side surface 38a of spectrometer beam splitter 38. In the beam splitter, the light is split equally between the two arms 42a, 42b. Beam splitter 38 may be achromatic over the spectral analyzation range. At the end of each arm 42a, 42b, the light is diffracted at the grating 40a and 40b respectively.

[0071] Each grating 40a, 40b may be arranged in first-order Littrow-con- figuration for a wavelength hi. lying in the spectral analyzation range Xmin ... Xmax of the spectrometer, i.e., light at said wavelength is first-order diffracted back parallel to the direction of the incoming light. This configuration reduces the angular spread of the diffracted components in respect to the axis of the arms.

[0072] The diffracted components from the gratings 40a, 40b travel back along the arms 42a, 42b. In beam splitter 38, half of their intensity is directed towards an exit 38b of beam splitter 38.

[0073] The diffracted components may pass optional camera optics (not shown) and arrive at a camera 44, where they generate interference patterns.

[0074] The interference patterns of the different pairs of diffracted components of equal wavelength have different spatial frequencies along camera 44.

[0075] Spectral analysis of the spatial spectral components in the image recorded by camera 44 allows to determine the spectral components of the light arriving in spatial heterodyne spectrometer 6.

[0076] The images recorded by camera 44 are processed by a computing device (not shown), which determines the spectrum of the light arriving at spatial heterodyne spectrometer 6.

[0077] Spectrometer 6 may comprise a spectrometer support 46 that holds spectrometer beam splitter 38, the elements in the arms 42a, 42b, and camera 44 in place.

[0078] In the shown embodiments, spectrometer 6 comprises, in each arm 42a, 42b, a transparent body 48a, 48b. These transparent bodies are described in the next section. Arm design

[0079] Each transparent body 48a, 48b is transparent over the whole spectral analyzation range in the sense that, in said range, it transmits less at least 75%, in particular less than 90%, of the light traveling forth and back along the arm, i.e., losses due to absorption, scattering, or reflection are small.

[0080] As can be seen from Figs. 1 and 2, each transparent body 48a, 48b extends all the way from beam splitter 38 to the grating 40a, 40b, with the grating 40a, 40b being arranged adjacent to and along the distal surface of the transparent body.

[0081] For a compact design and homogenous, reflection-free transmission, each transparent body 48a, 48b may be devoid of cavities and gaps in the whole region extending from the beam splitter 38 to the grating 40a, 40b.

[0082] Each transparent body 48a, 48b comprises at least a first body section 50a, 50b and a second body section 52a, 52b.

[0083] The body sections are of solid materials that are transparent for light in the spectral analyzation range.

[0084] Each body section may span a prismatic region of space.

[0085] In each arm, the first body section 50a, 50b is arranged adjacent to the proximal side of the second body section 52a, 52b. The distal side of the first body section 50a, 50b and the proximal side of the second body section 52a, 52b form a planar refractive interface 54a, 54b.

[0086] The interface 54a, 54b extends non-perpendicularly to the axial direction 56a, 56b of the respective arm. This axial direction 56a, 56b is defined as the direction of the incoming light as it is split by the semitransparent mirror 58 of beam splitter 38.

[0087] In each arm, the first body section 50a, 50b has, over the spectral analyzation range, a refractive index nl different from the refractive index n2 of the second body section. Hence the light from beam splitter 38 is refracted at interface 54a, 54b.

[0088] This refractive index difference allows the body sections 50a, 50b, 52a, 52b to act as field widening prisms as, e.g., described in US10908023B2.

[0089] For simple manufacturing (see below), the refractive interface 54a, 54b may extend, in all the directions perpendicular to the axial direction 56a, 56b, all the way through the transparent body 48a, 48b.

[0090] In each arm 42a, 42b, grating 40a, 40b is arranged adjacent to the distal surface of the transparent body 48a, 48b. In the embodiments shown, the grating 40a, 40b is arranged adjacent to the distal surface of the second body section 52a, 52b. This allows to robustly and compactly align the gratings 40a, 40b to the body sections 50a, 50b, 52a, 52b.

[0091] Fig. 2 shows the angle a between the planar refractive interface 54a, 54b and the axial direction 56a, 56b. The angle a is, as mentioned, larger than 0° and smaller than 90°, i.e., refractive interface 54a, 54b is tilted in respect to the axial direction in order to refract the light. Angle a may be selected according to the ratio nl / n2 of the refractive indices nl and n2 of the first and second body sections 50a, 50b and 52a, 52b to achieve the desired light refraction.

[0092] Often, angle a is between 5° and 45°.

[0093] Fig. 2 also shows the angle 0 between the surface normal of the distal side of the transparent body 48a, 48b and axial direction 56a, 56b. This angle 0 may be selected as a function of the grating spacing and the center wavelength of the spectral analyzation range.

[0094] In order to combine a good refraction at interface 54a, 54b with a small diffractive spread of the light at the gratings 40a, 40b, the (absolute value of) angle a may be larger than the (absolute value of) angle 0. The signs may, however, also be the same, in particular if high refractive index contrast and large grating spacings are used or if nl > n2 (see below).

[0095] The refractive indices nl, n2 of the first and second body sections 50a, 50b and 52a, 50b, respectively, may be selected according to the optical requirements. Generally, a large difference between nl and n2 allows to generate strong refraction without the need to strongly incline interface 54a, 54b in respect to axial direction 56a, 56b. Hence, the refractive indices nl, n2 of the first and second body sections may differ by at least 0.1, or even by at least 0.2, with this condition being fulfilled over the whole spectral analyzation range.

[0096] In some embodiments, as shown, e.g., in Figs. 2 and 3, nl may be selected to be smaller than n2. Using a larger refractive index n2 of the second body section 52a, 52b may allow to implement a more efficient grating at the distal surface of the second body section 52a, 52b. On the other hand, a lower refractive index nl will typically make the refractive index difference between the first body section 50a, 50b and the material of beam splitter 38 smaller, thereby reducing reflection at the interface (if any) between them.

[0097] In other embodiments (as shown, e.g., in Fig. 4) nl may be selected to be larger than n2, e.g., due to manufacturing reasons.

[0098] As shown in the embodiments of Figs. 2 - 4, beam splitter 38 may comprise a semitransparent mirror 58 formed at the interface of two splitter bodies 38a, 38b, and the first body sections 50a, 50b may be adjacent to distal surfaces of the two splitter bodies 38a, 38b, which allows to assemble the first and second body sections and the beam splitter in a robust, compact design.

[0099] In a very robust design, the first body sections 50a, 50b may be mounted (either integrally or, e.g., by adhesives) to the splitter bodies 38a, 38b.

[0100] To reduce strain and reflection at the interface between the first body sections 50a, 50b and the splitter bodies 38a, 38b, the splitter bodies 38a, 38b may be of the same material as the first body sections 50a, 50b.

[0101] In a very simple class of embodiments, illustrated in Fig. 3, the first body sections 50a, 50b may be integral with the splitter bodies 38a, 38b, i.e., the first body sections are formed by the distal regions of the splitter bodies 38a, 38b.

[0102] In the embodiments shown, each transparent body 48a, 48b includes one of the splitter body 38a, 38b, one of the first sections 50a, 50b, and one of the second sections 52a, 52b.

[0103] The transparent bodies 48a, 48b may, however, comprise further elements, such as additional prisms or plates integrated in the respective arms 42a 42b.

[0104] Gratings

[0105] In a simple design, as shown in Fig. 5, the gratings 40a, 40b may be surface gratings at the distal sides of the transparent bodies 48a, 48b.

[0106] In order to reduce the number of body sections in the transparent bodies 48a, 48b, the gratings 40a, 40b may be surface gratings at the distal sides of the second body sections 52a, 52b.

[0107] To enhance the efficiency of the gratings 40a, 40b, the distal side of the transparent bodies 48a, 48b may be coated with a reflective coating 60, such as a metallic coating.

[0108] In another class of embodiments, as illustrated in Fig. 6, the gratings 40a, 40b may be formed by or on grating carriers 62 separate from the second body sections 52a, 52b. The grating carriers 62 are mounted to the distal side of the second body section 52a, 52b. This allows to manufacture the gratings separate from the second body sections.

[0109] Hence, for some embodiments, in each arm, the grating 40a, 40b may be formed by a grating carrier 62 mounted to the distal side of the second body section 52a, 52b. Materials and manufacturing

[0110] The material of the first and second body sections 50a, 50b and 52a, 52 respectively, may be a polymer(s) to simplify manufacturing using one or more molding steps.

[0111] Suitable materials for the various body sections with the lower refractive index may, e.g., be one-component or two-component curable compounds, such as, e.g., available from Delo Industrie Klebstoffe GmbH & Co. KGAA, Germany.

[0112] As mentioned, the beam splitter 38 may comprise two splitter bodies 38a, 38b, which may also be of a polymer.

[0113] In other embodiments, glass may be used for some or all of these components.

[0114] In some embodiments, molding may be used to form one or both of the body sections 50a, 50b and / or 52a, 52b right on top of the proximal part next to it.

[0115] For example, in the embodiments of Fig. 2 and 4, the first body sections 50a, 50b may be molded onto the distal surfaces of the splitter bodies 38a, 38b, respectively, and the second body sections 52a, 52b may then be molded onto the distal sides of the first body sections 50a, 50b.

[0116] In the embodiment of Fig. 3, each splitter body 38a, 38b may be molded in one step, thereby also forming the first body section 50a, 50b. Then, the second body sections 52a, 52b may then be molded onto the distal sides of the first body sections 50a, 50b.

[0117] In the embodiment of Fig. 5, the grating 40a, 40b may be formed in the distal surface of the second body section 52a, 52b while molding the second body section. This can be accomplished by adding a suitable surface relief to the corresponding section of the mold.

[0118] Alternatively, the grating 40a, 40b may be applied after forming the second body section, e.g., using embossing or relief-stamping.

[0119] Alternatively, the grating 40a, 40b may be formed by machining the remote side of the second body section 52a, 52b after forming the second body section.

[0120] In yet another embodiment, the grating 40a, 40b may be manufactured separately, e.g., on a grating carrier 62 as shown in Fig. 6, and only then be applied to the second body section 52a, 52b. Notes

[0121] In the example above, the SHS spectrometer is used in a device for Raman spectroscopy. It may, however, also be used in other applications, e.g., for measuring fluorescence, luminescence, or phosphorescence or for assessing the spec- tral composition of other types of light.

[0122] While there are shown and described presently preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims.

Claims

Claims1. A spatial heterodyne spectrometer for spectrally analyzing incoming light in a spectral analyzation range comprising a spectrometer beam splitter (38), a first diffractive grating (40a), with a first arm (42a) of the spectrometer extending between the spectrometer beam splitter (38) and the first diffractive grating (40a), and a second diffractive grating (40b), with a second arm (42b) of the spectrometer extending between the spectrometer beam splitter (38) and the second diffractive grating (40b), wherein the spectrometer beam splitter (38) is adapted to split the incoming light along a first axial direction (56a) into the first arm (42a) and along a second axial direction (56b) into the second arm (42b), wherein each arm (42a, 42b) comprises a solid, transparent body (48a, 48b) that is transparent over the spectral analyzation range and extends from the spectrometer beam splitter (38) to the grating (40a, 40b), wherein each transparent body (48a, 48b) comprises a first body section (50a, 50b) having a first refractive index (nl) and a second body section (52a, 52b) having a second refractive index (n2) different from the first refractive index (nl), wherein the first and the second body sections (52a, 52b) are adjacent to each other and form a planar refractive interface (54a, 54b) between them, wherein the refractive interface (54a, 54b) is tilted in respect to the axial direction (56a, 56b), and wherein, in each arm (42a, 42b), the grating (40a, 40b) is arranged adjacent to and along a distal surface of the transparent body (48a, 48b).

2. The spectrometer of claim 1 wherein, in each arm (42a, 42b), the grating (40a, 40b) is a surface grating at the distal side of the transparent body (48a, 48b).

3. The spectrometer of claim 2 wherein the distal side is coated by a reflective coating (60), such as a metallic coating.

4. The spectrometer of any of the claims 2 or 3 wherein, in each arm (42a, 42b), the grating (40a, 40b) is a surface grating at a distal side of the second body section (52a, 52b).

5. The spectrometer of any of the claims 1 or 2 wherein, in each arm (42a, 42b), the grating (40a, 40b) is formed by a grating carrier (62) of the transparent body (48a, 48b) mounted to a distal side of the second body section (52a, 52b).

6. The spectrometer of any of the preceding claims wherein the refractive index (nl) of the first body sections (50a, 50b) is smaller than the refractive index (n2) of the second body sections (52a, 52b).

7. The spectrometer of any of the claims 1 to 5 wherein the refractive index (nl) of the first body sections (50a, 50b) is larger than the refractive index (n2) of the second body sections (52a, 52b).

8. The spectrometer of any of the preceding claims wherein the spectrometer beam splitter (38) comprises a semitransparent mirror (58) formed at an interface of two splitter bodies (38a, 38b), wherein the first body sections (50a, 50b) are adjacent to distal surfaces of the two splitter bodies (38a, 38b).

9. The spectrometer of claim 8 wherein the first body sections (50a, 50b) are mounted to the splitter bodies (38a, 38b).

10. The spectrometer of any of the claims 8 or 9 wherein the splitter bodies (38a, 38b) are the same material as the first body sections (50a, 50b).

11. The spectrometer of claim 10 wherein the first body sections (50a, 50b) are integral with the prism splitter bodies (38a, 38b).

12. The spectrometer wherein the refractive indices (nl, n2) of the first body sections (50a, 50b) and of the second body sections (52a, 52b) differ, over the spectral analyzation range, by at least 0.1, such as by at least 0.2.

13. The spectrometer of any of the preceding claims wherein, in each arm (42a, 42b), there is a first angle a between the axial direction (56a, 56b) and a surface normal of the refractive interface (54a, 54b) and a second angle 0 between the axial direction (56a, 56b) and a surface normal of the distal side, wherein the first angle a is larger than the second angle 0.

14. The spectrometer of any of the preceding claims wherein each transparent body (48a, 48b) is devoid of cavities and gaps in a whole region extending from the beam splitter (38) to the grating (40a, 40b).

15. The spectrometer of any of the preceding claims wherein, in each arm (42a, 42b), the refractive interface (54a, 54b) extends, in all directions perpendicular to the axial direction (56a, 56b) all the way through the transparent body (48a, 48b).

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