Compact raman spectrometer with integrated light source

Abstract

A Raman spectrometer comprises a support structure (10) of several molded, interconnected support elements (12 – 24). A light source (26) emits light at an excitation wavelength range and is arranged on the support structure (10). illumi- nation optics (28a – 28d) mounted in the support structure (10) projects light from the light source (26) through a sensing port (30) onto a target (8) where Raman scattering occurs. Some of the Raman-scattered light is fed through a filter assembly (32, 78, 80, 82a, 82b) arranged in the support structure (10), which blocks light in the excitation wavelength range. The light is collimated in collimation optics (34a – 34c) arranged in the support structure (10). A spatial heterodyne spectrometer (36) arranged in the support structure (10) receives the collimated and filtered light for spectral analysis. Lenses (28a – 28d) of the illumination optics may be of glass while lenses (34a, 34b) of the collimation optics (34a – 34c) may be of plastics.

Description

[0001] Compact Raman spectrometer with integrated light source

[0002] Technical Field

[0003] The invention relates to a Raman spectrometer with a light source, illumination optics, collimation optics, and a spatial heterodyne spectrometer.

[0004] Background Art

[0005] US10908023B2 and US11719626B2 describe devices for performing spatial heterodyne spectrometry (SHS) suitable for Raman spectroscopy applications. They are adapted to analyze the spectral composition of Raman-scattered light.

[0006] SHS spectrometers comprise a beam splitter dividing the incoming light between 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 diffracted light returns to the beam splitter where it is overlapped with its counterpart from the other arm.

[0007] 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.

[0008] Disclosure of the Invention

[0009] The problem to be solved by the present invention is to provide a Raman spectrometer that can be compact and is well-suited for mass production, such as consumer-scale mass production, e.g., as a component in a wearable device.

[0010] This problem is solved by the spectrometers according to the independent claims.

[0011] Hence, in a first aspect, a Raman spectrometer is provided that comprises at least the following elements: - A support structure of several molded, interconnected support elements: The support structure forms the framework for holding the following components in place.

[0012] - A light source arranged on the support structure: The light source may be used to generate excitation light in an excitation wavelength range.

[0013] - A sensing port: The sensing port is adapted for the passage of light towards and from a target.

[0014] - Illumination optics arranged in the support structure: The illumination optics is adapted to project light from the light source through the sensing port towards the target.

[0015] - A filter assembly arranged in the support structure and positioned to receive light returning from the target: The filter assembly is adapted to block light in the excitation wavelength range, thereby preventing all or most of it from reaching the spectrometer (see below).

[0016] - Collimation optics arranged in the support structure: The collimation optics is adapted to collimate the light returning from the target.

[0017] - A spatial heterodyne spectrometer arranged in the support structure. The spectrometer is positioned to receive collimated and filtered light after the light has passed through the collimation optics and the filter assembly.

[0018] This design is on the concept of integrating all of the light source, illumination optics, filter assembly, collimation optics, and SHS spectrometer in a common support structure, thereby making the device easier to handle during manufacturing and when mounting into a surrounding device, even at large volumes. For its potential of robustness and compactness, the design is particularly suited for wearable devices.

[0019] The spectrometer may have a dichroic beam splitter arranged in the support structure along a path of the light from the light source towards sensing port and along a path of the returning light from the sensing port towards the collimation optics. The dichroic beam splitter is adapted to direct Raman-scattered light in the returning light towards the collimation optics but not light with a wavelength that is within the excitation wavelength range. Hence, the beam splitter forms part of the filter assembly and, at the same time, controls the splitting of light between the light source, the target, and the collimation optics.

[0020] At least one of the support elements of the support structure may comprise an interior space extending along an axial direction of the support element, and it may hold several optical components arranged in the interior space along the element axis. This design can be used to efficiently align the optical components along the axial direction, and it also protects the components.

[0021] In a second aspect, a Raman spectrometer is provided that may or may not heave the features of the first aspect. It comprises at least the following elements:

[0022] - A light source: The light source may be used to generate excitation light in an excitation wavelength range.

[0023] - A sensing port: The sensing port is adapted for the passage of light towards and from a target.

[0024] - Illumination optics: The illumination optics is adapted to project light from the light source through the sensing port towards a target. It comprises at least one illumination lens.

[0025] - A filter assembly positioned to receive light returning from the target: The filter assembly is adapted to block light with wavelengths within in the excitation wavelength range, thereby preventing all or most of it from reaching the spectrometer (see below).

[0026] - Collimation optics: The collimation optics is adapted to collimate the light returning from the target. It comprises at least one collimation lens.

[0027] - A spectrometer positioned to receive collimated and filtered light after having passed through the collimation optics and the filter assembly.

[0028] The filter assembly comprises a first filter element arranged between the sensing port and the collimation optics.

[0029] Further, in this second aspect, every illumination lens is of glass. In addition, at least one collimation lens is of plastics. If there are several collimation lenses, all of them may optionally be of plastics.

[0030] This design is based on the understanding that a spectrometer of this type can, advantageously, combine glass and plastic lenses. The glass lenses are used in the collimation optics where the intensity of the light from the light source is high. Glass as a lens material reduces the risk of generating large amounts of undesired Raman scattering in the lenses. On the other hand, cheaper and easier-to-shape plastic lenses may be applied after the first filter element because, there, the intensity of the excitation light is much lower and, therefore, the risk of generating Raman radiation of a significant level in the lenses is lower.

[0031] Brief Description of the Drawings The invention will be better understood and objects other than those set forth above will become apparent when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings, wherein:

[0032] Fig. 1 shows a sectional view of an embodiment of a Raman spectrometer,

[0033] Fig. 2A and 2B show embodiments of an end section of a first support element,

[0034] Fig. 3 shows a sectional view of the end section of the first support element of Fig. 2B and a matching part of a second support element,

[0035] Fig. 4 shows a sectional view of a support element,

[0036] Fig. 5 shows a sectional view of embodiments of an arm support element and the components it holds, and

[0037] Fig. 6 shows a sectional view of embodiments of a sensing port.

[0038] Modes for Carrying Out the Invention

[0039] Definitions

[0040] The term "transversal" is to be understood as "non-parallel".

[0041] The term "prism beam splitter" designates a beam splitter formed at the interface of two prism-shaped elements, such as a cube beam splitter.

[0042] Raman Spectrometer

[0043] Fig. 1 illustrates the design of some embodiments of a Raman spectrometer.

[0044] The shown spectrometer comprises functional sections including an illumination section 2, a collimator section 4, and a spectrometer section 6.

[0045] Illumination 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 include Raman-scattered light.

[0046] Collimation section 4 is adapted to collimate the returning light, preparing it for entry into spectrometer section 6.

[0047] Spectrometer section 6 is adapted to spectrally analyze the light from collimator section 4. The spectrometer further comprises a support structure 10 including several molded, interconnected support elements 12 - 24.

[0048] In the following sections, the functional sections 2 - 6 as well as the support structure 10 are described in more detail.

[0049] Illumination Section

[0050] Illumination section 2 comprises a light source 26 emitting light at an excitation wavelength range.

[0051] The excitation wavelength range is centered around a center excitation wavelength Ao and has a full-width-half-maximum range A2.

[0052] For Raman spectroscopy, AX may be small for good resolution, such as smaller than 5 nm or even smaller than 1 nm.

[0053] Ao depends on the application.

[0054] For glucose detection, for example, Ao 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 ').

[0055] In another example, Ao may be between 825 and 835 nm, such as 830 nm, where cost-effective lasers are available and lay 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 ').

[0056] It may also be useful to extend the spectral analyzation range, e.g., up to 3000 cm1in order to use further parts of the Raman spectrum to improve the quality of the sensor signal (e.g., of a biomarker, such as using the water peak to determine the excited tissue volume).

[0057] 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.

[0058] Light source 26 may, e.g., be a vertical -cavity surface-emitting laser (VCSEL) for its compact size, narrow bandwidth, mass-production capabilities, and large light power.

[0059] Illumination section 2 further comprises illumination optics 28a - 28d, which is adapted to project light from light source 26 through a sensing port 30 towards target 8 in order to generate Raman scattered light in the target.

[0060] Note that the number of lenses in the illumination optics 28a - 28d depends on implementation and may also differ from four. For example, only a single lens may be used before and / or after the beam splitter. Sensing port 30 may be formed by an opening in support structure

[0061] 10.

[0062] Sensing port 30 may be closed by a window 34 that is transparent for the light from light source 26 as well as for the Raman-scattered light from target 8. Window 34 may be held by support structure 10, in particular by the second illumination support element 14 as described in more detail below.

[0063] To reduce undesired Raman scattering, window 34 may be of glass or of another material with low Raman scattering.

[0064] In the shown type of embodiments, part of illumination optics 28a - 28d (namely the lenses 28c, 28d in the shown embodiment) process both the light from light source 26 on its way to target 8 as well as the scattered light returning from target 8. Therefore, illumination section 2 further comprises a dichroic beam splitter 32 for separating light in the excitation wavelength range from the returning Raman- scattered light.

[0065] In the shown type of embodiments, dichroic beam splitter 32 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 section 4.

[0066] 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 26 and collimator section 4 may be swapped in their positions.

[0067] 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 32 may be dispensed with.

[0068] If a dichroic beam splitter 32 is used, as shown, a first part 28a, 28b of the illumination optics may be arranged on the path of the light between light source 26 and dichroic beam splitter 32, and a second part 28c, 28d of the illumination optics may be arranged on the path of the light between dichroic beam splitter 32 and sensing port 30. The first part 28a, 28b is adapted to collimate the light from light source 26 at dichroic beam splitter 32 while the second part 28c, 28d is adapted to focus the light from dichroic beam splitter 32 to a focal point 33 at sensing port 30.

[0069] It must be noted that this collimation and focusing, as it is implemented by illumination optics 28a - 28d, will not be perfect because light source 26 is an extended light source, e.g., with an area in a range between 0.1 x 0.1 mm2and 2 x 2 mm2(as compared to an aperture diameter Da of the illumination optics of, e.g., between 3 and 6 mm).

[0070] As mentioned, the illumination optics 28a - 28d may be adapted to focus the light from the light source 28 at a focal point 33. For safety reasons, and as shown in Fig. 6, focal point 33 may be located within an exterior side 30a of the sensing port, i.e., within the convex hull of the section of the support structure 10 that forms the sensing port 30 (i.e., within the convex hull of second end 14b of second illumination support element). This reduces the risk of excessively high radiation on target 8 because the light leaving the spectrometer is divergent.

[0071] Illumination section 2 may further comprise a bandpass filter for excitation wavelength / lo, i.e. for the excitation wavelength range, such as a Fabry Perrot filter, for narrowing, if desired, the spectral width of the excitation light if a wider- wavelength light source 26 is used. Such a bandpass filter may, e.g., be formed by beam splitter 32, thereby making dichroic beam splitter 32 even more wavelength-selective.

[0072] Collimation Section

[0073] Collimation section 4 receives Raman-scattered light from illumination section 2. In the shown embodiment, it comprises collimation optics 34a - 34c, with 34a, 34b being convex lenses and 34c being a pinhole. The distances between pinhole 34c and each lens 34a and 34b are equal to the focal lengths of the lenses 34a, 34b, respectively.

[0074] Collimation optics 34a - 34c 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 section 6.

[0075] To do so, the already partially collimated light entering collimator section 4 is focused at pinhole 34c, which spatially filters out the poorly collimated light components, whereupon it is again collimated by lens 34b.

[0076] The aperture diameter of pinhole 34c may, e.g., be less than 3 mm or even less than 1 mm. In other embodiments, pinhole 34c may be annular to collect light from a ring area at the skin and not necessarily from the focal spot.

[0077] In a compact design, collimation axis Ac may extend transversally, in particular perpendicularly, to the illumination axis Ai of illumination section 2, with the illumination axis Ai being defined as extending from light source 26 to sensing port 30. Spectrometer Section

[0078] Spectrometer section 6 is adapted to analyze the spectrum of the light from collimator section 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.

[0079] In a typical example, the spectral analyzation range may be between 239 cm1and 2213

[0080] Spectrometer section 6 comprises a spatial heterodyne spectrometer 36. This type of spectrometer has a compact design with good resolution and does not need any moving parts. Such interferometers 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

[0081] US5059027A or US10908023B2.

[0082] Spatial heterodyne spectrometers are, for their compactness, robustness, and lack of movable parts, well suited for compact, wearable devices.

[0083] 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.

[0084] The spectrometer may further comprise two field-widening prisms 44a, 44b, with one prism arranged in each arm 42a, 42b between spectrometer beam splitter 38 and the grating 40a and 40b, respectively.

[0085] 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.

[0086] Each grating 40a, 40b may be arranged in first-order Littrow-con- figuration for a wavelength Ai. lying in the spectral analyzation range, 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.

[0087] The prisms 44a, 44b improve, as known, the quality of the reconstructed spectrum and allow more throughput (etendue, especially angle of incidence). 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.

[0088] The diffracted components may pass optional camera optics 46 and arrive at a camera 48, where they generate interference patterns.

[0089] The interference patterns of the different pairs of diffracted components of equal wavelength have different spatial frequencies along camera 48.

[0090] As, for example, described in the above article by C.-A. Stbckling et al. as well as the prior art cited earlier, a spectral analysis of the spatial spectral components in the image recorded by camera 46 allows to determine the spectral components of the light arriving in spatial heterodyne spectrometer 36.

[0091] Camera optics 46, which may be a simple lens, allows to increase the overlap of the pairs of diffracted components arriving at camera 48. It projects the region of the gratings 40a, 40b onto the plane of camera 48. As mentioned, camera optics 46 is, however, optional.

[0092] The images recorded by camera 48 are processed by a computing device (not shown), which determines the spectrum of the light arriving at spatial heterodyne spectrometer 36.

[0093] Support Structure

[0094] As mentioned, the spectrometer may comprise a support structure 10 including several molded, interconnected support elements 12 - 24. Possible aspects of the design of this support structure and its elements are discussed in the following.

[0095] Support structure 10 may include several features that, alone and / or in combination, simplify the manufacturing process and allow to build a highly compact spectrometer.

[0096] For example, building a support structure of several molded support elements and, optionally, other parts, streamlines the manufacturing process because molded support elements are easy to manufacture in large numbers even if they have complex shape.

[0097] In the following, the support elements of the various functional sections 2, 4, and 6 are described in more detailed.

[0098] In the shown embodiment, illumination section 2 has three illumination support elements 12, 14, and 16.

[0099] For example, there may be a first illumination support element 12 holding a first part 28a, 28b of the illumination optics. This first part may, as shown, be the lenses 28a, 28b of the illumination optics that are arranged along the light path between light source 26 and dichroic beam splitter 32.

[0100] At a first end 12a, first illumination support element 12 may be connected to light source 26. In the shown example, the first end 12a of first illumination support element 12 is connected to a carrier member 50, such as a plate, that holds light source 26.

[0101] Further, there may be a second illumination support element 14 holding a second part 28c, 28d of the illumination optics. This second part may, as shown, be the lenses 28a, 28b of the illumination optics that are arranged along the light path between dichroic beam splitter 32 and sensing port 30.

[0102] Further, there may be a third illumination support element 16 holding dichroic beam splitter 32. The third illumination support element 16 may be arranged (along the light path from light source 26) between the first and second support elements 12, 14.

[0103] If dichroic beam splitter 32 is used in transmission for the light from light source 26, the first and the second illumination support elements, 12, 14 are mounted to opposite sides of the third illumination support element 16.

[0104] The first and second illumination support elements 12, 14 may have cylindrical or at least rotationally symmetric outer surfaces and / or be provided with screw connectors for connecting them to third illumination support element 16 and / or carrier member 50.

[0105] On the other hand, third illumination support element 16 may have one or more substantially planar outer surfaces, e.g., on its side facing collimator section 4. The wall 16a on that side may have an opening 16b for the passage of the scattered light from target 8. This simplifies connecting third illumination support element 16 to collimator section 4 as described below.

[0106] In particular if dichroic beam splitter 32 is a prism beam splitter, third illumination support element 16 may have four substantially flat walls extending, e.g., parallel to illumination axis Ai, between the first and second illumination support elements 12, 14.

[0107] Collimation section 4 may have a single collimation support element 18 holding the collimation optics 34a, 34b, 34c.

[0108] Collimation support element 18 may be directly mechanically mounted to third illumination support element 16, which simplifies mutual alignment.

[0109] Collimation support element 18 may have a cylindrical or at least rotationally symmetric outer surface and / or be provided with a screw connector at a first end 18a for connecting it the illumination section 2, e.g., to the third illumination support element 16 as shown in Fig. 1. In addition or alternatively thereto, collimation support element 18 may be provided with a screw connector at a second end 18b for connecting it to spectrometer section 6. More details about such connectors are provided below.

[0110] Collimation support element 18 may hold the two collimation lenses 34a, 34b as well as pinhole 34c between them for ease of assembly and accurate mutual alignment.

[0111] Spectrometer section 6 may have an analyzer support element 20 that holds the spatial heterodyne spectrometer 10.

[0112] Collimation support element 18 and analyzer support element 20 may be directly mechanically mounted to each other, which simplifies mutual alignment.

[0113] Analyzer support element 20 may hold spectrometer beam splitter 38.

[0114] The support structure of spectrometer section 6 may further comprise two arm support elements 22a, 22b, each of which holds one grating 40a, 40b and one prism 44a, 44b, thereby allowing to separately assembly, in accurate mutual alignment, each grating 40a, 40b and its respective prism 44a, 44b. More details on the arm support elements 22a, 22b are provided below.

[0115] Alternatively, the prisms and / or gratings may be directly mounted to analyzer support element 20 and / or to spectrometer beam splitter 38.

[0116] The support structure of spectrometer section 6 may further comprise a camera support element 24, which is mounted to analyzer support element 20, e.g., screwed thereto.

[0117] Camera support element 24 may hold camera 48 as well as (if present) camera optics 46. A camera holder 52 may be provided for mounting camera 48 and connecting it to camera support element 24.

[0118] Support Element Interconnections and Design

[0119] As mentioned, support structure 10 comprises a number of molded, interconnected support elements.

[0120] To simplify manufacturing and assembly, at least some of these support elements may be single pieces, i.e., not assembled from separate pieces but cast as one piece. For example, the following support elements may be single piece elements: first, second, and third illumination support elements 12, 14, 16, collimation support element 18, arm support elements 22a, 22b, and / or camera support element 24. Analyzer support element 20 may, e.g., be assembled from several pieces. However, it also may be a single-piece element.

[0121] For reduced cost and weight, at least some, or all, of the support elements 12 - 24 may of a plastic.

[0122] The support elements may be glued or welded to each other, but other fastening mechanisms may be used as well. Gluing provides a very simple type of connection. Hence, in some embodiments, at least two of the support elements 12 - 24 are glued to each other.

[0123] For good performance, special measures may be provided for ensuring a proper mutual alignment of the support elements. For example, maintaining the correct distance between the first illumination support element 12 (and the lenses 28a, 28b therein) and light source 26 improves the light collimation at beam splitter 32. Similarly, a correct angular alignment between collimation support element 18 and illumination section 2 improves the efficiency of collimator section 4.

[0124] One measure to implement efficient alignment is illustrated in Fig. 2A, and another one is illustrated in Figs. 2B and 3, for the example of end section 18b of collimation support element 18. Even though the figures show the concepts for end section 18b, the same concept may also be used for, e.g., any of the following end sections:

[0125] - The rear end section 12a of first illumination support element 12.

[0126] - Front end section 12b of first illumination support element 12, i.e., the section connected to third illumination support element 16,

[0127] - The rear end section 14a of second illumination support element 14, i.e., the section connected to third illumination support element 16.

[0128] - Front end section 14b of second illumination support element 14, i.e., the section at sensing port 30.

[0129] - Rear end section 18a of collimation support element 18, i.e., the section connected to third illumination support element 16.

[0130] - Rear end section 24a of camera support element 24, i.e., the section connected to analyzer support element 20.

[0131] - Front end section 24b of camera support element 24, i.e., the section connected to camera holder 52.

[0132] Similar designs may also be used for the arm support members 22a, 22b, see below.

[0133] In the embodiment of Fig. 2A, as can be seen, end section 18b comprises three projections 54a (i.e., three protrusions), 54b, 54c axially projecting over the end surface 56, with each of these projections having an axial end surface area much smaller (e.g., at least ten times smaller) than the area of end surface 56, thereby forming three contact points.

[0134] When end section 18b is axially held (such as by glue) against a surface of a next support element, e.g., against analyzer support element 20, the projections or contact points 54a, 54b, 54c will define the relative angular and axial alignment of the two support elements 18, 20. The two elements can then be fixed together, e.g., by means of gluing or welding.

[0135] During manufacturing, it is tested, at least on some manufactured parts, if the relative angular and axial alignment of the two support elements 18, 20, as governed by the location of the three contact points, are within the desired specifications, e.g., by measuring the optical performance of the parts. If it is found that the alignment does not match the desired specifications, the mold for support element 18 can be locally corrected at the contact points, e.g., user laser ablation, mechanical machining, or plating techniques, to adjust the length of the projections. Hence, the relative alignment of the two support elements 18, 20 can be tuned without a need to rework the complete mold(s).

[0136] In the embodiment of Fig. 2B and 3, end section 18b comprises screw thread 58, e.g., an outer screw thread as shown.

[0137] The next support element, in this case analyzer support element 20, comprises a recess or opening 60, e.g., an annular recess, with a matching screw thread 62, e.g., an inner screw thread, which is dimensioned to receive end section 18b and to form a screw connection therewith.

[0138] In that case, end surface 56 will define the relative angular and axial alignment of the two support elements 18, 20. Again, end surface 56 may be optimized, by treating the mold, as mentioned for the projections 54a - 54c above.

[0139] In a further example, the embodiments of Figs. 2A and 2B may be combined by equipping end section 18b with both the projections 54a - 54c and the screw thread 58. In this case, collimation support element 18 can be screwed into analyzer support element 20. When the screw connection is tightened, collimation support element 18 will be axially held against analyzer support element 20, with the projections or contact points 54a, 54b, 54c being pushed against a counter surface 64 of analyzer support element 20.

[0140] As will be understood, as long as the screw threads 58, 62 provide enough clearance, it will be the exact length of the projections 54a, 54b, 54c that will define the relative angular and axial alignment of the two support elements 18, 20.

[0141] After screwing the two support elements 18, 20 of Figs. 2B and 3 together, they may be glued and / or welded for stabilizing the connection. A similar technique can also be used without screw threads. This is illustrated in Fig. 5. That figure, which will be described in more detail below, is a sectional view of one of the arm support element 22a, which holds grating 40a and (optionally) prism 44a. Its first end 66a facing spectrometer beam splitter 38, has three projections (two of which, 54a, 54b are shown in Fig. 5) forming three contact points. These projections rest against a surface of spectrometer beam splitter 38.

[0142] Arm support element 22a is axially biased against spectrometer beam splitter, e.g., by means of an elastically compressed spring member between second end 66b of arm support element 22a and analyzer support element 20.

[0143] Hence, again, the alignment of parts 22a and 38 is controlled by exactly three contact points, the position of which can easily be corrected by locally tuning the mold of arm support element 22a.

[0144] Hence, in more general terms, for accurately aligning a support member with an adjoining part of the spectrometer, at least one of the support elements may be axially biased against at least the adjoining part and axially contacts the adjoining part at exactly three contact points 54a, 54b, 54c. This design can, e.g., be used to provide an accurate alignment between two support elements if the adjoining part is another one of the support elements.

[0145] The three contact points may, e.g., be formed by three projections on the one support element.

[0146] Fig. 4 illustrates some of the possible design aspects of one or more of the support elements 12 - 24. Again, the figure shows these aspects for collimation support element 18, but the same concepts may, e.g., be readily used for the first and second illumination support elements 12, 14, the arm support elements 22a, 22b, and / or the camera support element 24.

[0147] Here, the support element 18 forms an interior space 70 radially surrounded by the support element 18 and extending along axial direction A of the support element 18.

[0148] The interior space 70 may extend between two openings 72a, 72b at opposite ends 18a, 18b of support element 18, which form the passages for the light passing through the support element.

[0149] The presence of such an interior space 70 simplifies the alignment of the optical components held therein, and it keeps them aligned and protects them from external influences, such as humidity and / or dust.

[0150] If support element 18 surrounding interior space 70 is non-transparent at least for light in the spectral analyzation range, it may improve measurement accuracy by keeping out undesired stray light. For ease of manufacturing, interior space 70 may be formed by an integral support element, i.e., the support element surrounding interior space 70 is of a single piece.

[0151] At least some of the optical components 34a, 34b, 34c within interior space 70 may be stacked against each other by means of spacers 74a - 74c. In the shown embodiment, where the optical components 34a - 34c are of plastics, the spacers 74a - 74c may be integral parts of the optical components. Alternatively, though, such as when at least some of the optical components are of glass, separate spacers may be used.

[0152] During assembly, the spacer elements 74a, 74b, 74c are movable along axial direction A in interior space 70, and they are locked in place after assembly, e.g., when the support element 18 is mounted to another part of the spectrometer.

[0153] Support element 18 may comprise at least one ledge 76 acting as an axial abutment for at least one of the optical components 34a - 34c and / or spacers 74a - 74c.

[0154] In a compact design, support element 18 may have a cylindrical wall surrounding interior space 70. Alternatively or in addition thereto, such a cylindrical wall may, e.g., also be used for the support elements 12, 14, 22a, 22b, and / or 24.

[0155] Arm Support Elements

[0156] As mentioned, the spectrometer may comprise arm support elements 22a, 22b. Fig. 5 shows some aspects that may, in some embodiments, be included in such arm support elements.

[0157] Each arm support element 22a, 22b may hold one grating 40a, 40b and one prism 44a, 44b, such that a grating and its prism may be prefabricated, optionally be tested, and only then be inserted into analyzer support element 20.

[0158] For example, steps in the arm support elements 22a, 22b may form ledges to position the components, and / or spacers may be used, and a retainer cap 67 may be provided to fix the grating 40a, 40b. The components may also be glued in place.

[0159] For example, the grating 40a, 40b and its prism 44a, 44b may be glued to each other and then be inserted into the respective arm support element 22a, 22b as shown.

[0160] Alternatively, in particular if prism 44a, 44b is of a plastics material, it may also be of a single piece with arm support element 22a, 22b if arm support element 22a, 22b is of a transparent material. In other embodiments, prism 44a, 44b may be of glass, in which case a design such as shown in Fig. 5 may be used.

[0161] In other embodiments, grating 40a, 40b can be directly mounted to the surface of prism 44a, 44b that faces away from spectrometer beam splitter 38.

[0162] Also, prism 44a, 44b may be an integral part of beam splitter 38.

[0163] Filter Assembly

[0164] As mentioned, the spectrometer comprises a filter assembly arranged in the support structure 10, which is positioned to receive light returning from target 8 and adapted to block light in the excitation wavelength range, i.e., to block light from light source 26.

[0165] There are various sections in the spectrometer where elements of the filter assembly may be located. For a good suppression of the light in the excitation wavelength, several such elements may be arranged in series. Some such elements are described in the following - they may be used individually or in combination.

[0166] These elements may not only block light in the excitation wavelength range. They may also block light at other wavelengths if these wavelengths fall outside the spectral analyzation range. For example, they may block visible light or far-infrared light if the spectral analyzation range is in the near infrared.

[0167] However, the filter assembly should be adapted to pass light in the spectral analyzation range of the spectrometer.

[0168] One element of the filter assembly may be the dichroic beam splitter 32. As mentioned, it is designed to prevent light in the excitation wavelength range from entering collimator section 4.

[0169] Since dichroic beam splitter 32 may not be able to prevent all light in the excitation wavelength and / or in other undesired wavelength ranges from entering collimator section 4, further elements may be added to the filter assembly.

[0170] If dichroic beam splitter 32 is a prism beam splitter, one such element may, e.g., be a filter coating 78 (see Fig. 1) arranged on the exit surface 32a of the dichroic beam splitter 32, with the exit surface 32a being the surface facing collimation optics 34a, 34b, 34c. Such a filter coating obviates the need to separately install a filter component.

[0171] In addition, or alternatively, such a filter coating 80 (Fig. 1) may be arranged on any of the surfaces of spectrometer beam splitter 38, such as on entry side surface 38a. In addition, or alternatively, such a filter coating may also be arranged on any of the surfaces of the spectrometer beam splitter 38.

[0172] In addition or alternatively thereto, the filter assembly may comprise separately mounted filter elements 82a, 82b, e.g., arranged in collimator section 4, as shown in dashed lines in Fig. 1.

[0173] Lens Material

[0174] As mentioned, the various lenses of the spectrometer may be glass or plastics.

[0175] To reduce an undesired generation of large amounts of Raman-scattered light within the lenses, any lenses arranged before the first filter of the filter assembly may be of glass. Such lenses are more expensive to manufacture and integrate in the device, but they are less prone to generate Raman scattering.

[0176] A glass material with very low Raman scattering is sapphire, and, therefore, the glass for these lenses may be sapphire glass.

[0177] Hence, at the lens or lenses 28a - 28d of the illumination optics, i.e., the illumination lens(es), may be of glass.

[0178] On the other hand, the lenses after the first filter element (which, in the embodiment of Fig. 1, is the dichroic beam splitter 32), may be of plastics, which reduces costs and offers a larger choice of non-spherical surfaces.

[0179] Hence, at least some of the lenses 34a, 34b of the collimation optics (i.e., the collimation lenses) may be of plastics, with the first filter element being arranged between sensing port 30 and the collimation optics.

[0180] Every one of the collimation lenses 34a, 34b may be of plastics.

[0181] Notes

[0182] As mentioned, various techniques may be used to properly align one of the support elements 12 - 24 with a neighboring part of the spectrometer, such as with another support element, e.g., using the projections 54a, 54b, 54c (contact points) as described above.

[0183] If alignment is crucial, active actuators may be provided between a support element at its adjacent part. For example, and as indicated in Fig. 1, one or more electrically controllable actuators 84 may be located between camera support element 24 and camera 48. The actuator(s) 84 may, e.g., be controlled to optimize the contrast of an interference pattern as it appears on the image of camera 48. As mentioned, the support elements 12 - 24 may be welded or glued to each other and / or to other parts of the spectrometer.

[0184] During assembly, machine vision may be used to automatically align parts, e.g., using markers affixed to the parts. 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 Raman spectrometer comprising a support structure (10) of several molded, interconnected support elements (12 - 24), a light source (26) emitting light at an excitation wavelength range and being arranged on the support structure (10), a sensing port (30) adapted for passage of light towards and from a target, illumination optics (28a - 28d) arranged in the support structure (10) and adapted to project light from the light source (26) through the sensing port (30) towards a target, a filter assembly (32, 78, 80, 82a, 82b) arranged in the support structure (10) and positioned to receive light returning from the target and adapted to block light in the excitation wavelength range, collimation optics (34a - 34c) arranged in the support structure (10) and adapted to collimate the light returning from the target, a spatial heterodyne spectrometer (36) arranged in the support structure (10) and positioned to receive collimated and filtered light after having passed through the collimation optics (34a - 34c) and the filter assembly (32, 78, 80, 82a, 82b).

2. The spectrometer of claim 1 wherein the sensing port (30) is formed by an opening in the support structure (10).

3. The spectrometer of any of the preceding claims further comprising a window (34) arranged at the sensing port (30).

4. The spectrometer of claim 3 wherein the window (34) is arranged in the support structure (10).

5. The spectrometer of any of the preceding claims further comprising a dichroic beam splitter (32) arranged in the support structure (10) along a path of the light from the light source (26) towards sensing port (30) and along a path of the returning light from the sensing port (30) towards the collimation optics (34a - 34c), wherein the dichroic beam splitter (32) is adapted to direct Raman-scattered light inthe returning light towards the collimation optics (34a - 34c) but not light in the excitation wavelength range.

6. The spectrometer of claim 5 wherein the dichroic beam splitter (32) passes light at the excitation wavelength range and reflects Raman-scattered light from the target towards the collimation optics (34a - 34c).

7. The spectrometer of any of the claims 5 or 6 wherein the dichroic beam splitter (32) is arranged in a light path between a first and a second lens (28a, 28b; 28c, 28d) of the illumination optics (28a - 28d).

8. The spectrometer of any of the claims 5 to 7 wherein the dichroic beam splitter (32) is a prism beam splitter and wherein the filter assembly (32, 78, 80, 82a, 82b) comprises a filter coating (78) on an exit surface (32a) of the prism beam splitter facing the collimation optics (34a - 34c).

9. The spectrometer of any of the claims 5 to 8 wherein a first part (28a, 28b) of the illumination optics (28a - 28d) is arranged on a path of light between the light source (26) and dichroic beam splitter (32), and a second part (28c, 28d) of the illumination optics (28a - 28d) is arranged on a path of light between the dichroic beam splitter (32) and the sensing port (30), wherein the first part (28a, 28b) is adapted to collimate the light from the light source (16) at the dichroic beam splitter (32) while the second part (28c, 28d) is adapted to focus the light from the dichroic beam splitter (32) to a focal point (33) at the sensing port (30)10. The spectrometer of any of the preceding claims wherein an illumination axis (Ai) extending from the light source (26) to the sensing port (30) extends transversally, in particular perpendicularly, to a collimation axis (Ac) of the collimation optics (34a - 34c).

11. The spectrometer of any of the preceding claims wherein at least one of the support elements (12 - 24) forms an interior space (70) extending along an axial direction (A) of the support element (12 - 24) and holds, in the interior space (70), several optical components (34a, 34b, 34c) along the axial direction (A).

12. The spectrometer of claim 11 wherein the interior space (70) is formed by an integral support element.

13. The spectrometer of any of the claims 11 or 12 wherein, in the interior space (70) at least some of the optical components (34a, 34b, 34c) are stacked against each other via spacer elements (74a - 74c), wherein the spacer elements (74a - 74c) are movably arranged within the interior space (70).

14. The spectrometer of any of the preceding claims comprising a first illumination support element (12) holding at least part (28a, 28b) of the illumination optics (28a - 28d).

15. The spectrometer of claim 14 comprising a second illumination support element (14) holding part (28c, 28d) of the illumination optics (28a - 28d).

16. The spectrometer of the claims 5 and 15 comprising a third illumination support element (16) holding the dichroic beam splitter (32), wherein the third illumination support element (16) is arranged between the first and the second illumination support elements (12, 14).

17. The spectrometer of any of the preceding claims comprising a collimation support element (18) holding the collimation optics (34a - 34c).

18. The spectrometer of claim 17 wherein the collimation optics (34a - 34c) comprises a pinhole (34c) between at least two collimation lenses (34a, 34b), wherein the pinhole (34c) and the collimation lenses (34a, 34b) are arranged in the collimation support element (18).

19. The spectrometer of the claim 16 and of any of the claims 17 or 18 wherein the third illumination support element (16) and the collimation support element (18) are directly mechanically mounted to each other.

20. The spectrometer of any of the preceding claims further comprising an analyzer support element (20) holding the spatial heterodyne spectrometer21. The spectrometer of any of the claims 18 or 19 and of claim 20 wherein the collimation support element (18) and the analyzer support element (20) are directly mechanically mounted to each other22. The spectrometer of any of the preceding claims wherein the spatial heterodyne spectrometer (10) comprises a spectrometer beam splitter (38).

23. The spectrometer of claim 22 wherein the filter assembly (32, 78, 80, 82a, 82b) comprises a filter coating (80) on a surface of the spectrometer beam splitter (38).

24. The spectrometer of any of the claims 22 or 23 wherein the spatial heterodyne spectrometer (36) comprises two gratings, two prisms (40a, 40b), and two arm support elements (22a, 22b), wherein each arm support elements (22a, 22b) holds one grating (40a, 40b) and one prism (44a, 44b), and wherein the arm support elements (22a, 22b) are biased against the spectrometer beam splitter (38).

25. The spectrometer of any of the preceding claims wherein the illumination optics (28a - 28d) is adapted to focus the light from the light source (26) at a focal point (33) wherein the focal point (33) lies within an exterior side (30a) of the sensing port (30).

26. The spectrometer of any of the preceding claims wherein at least two of the support elements (12 - 24) are glued to each other.

27. The spectrometer of any of the preceding claims wherein at least a one of the support elements (12 - 24) is axially held against at least an adjoining part of the spectrometer and axially contacts the adjoining part at exactly three contact points (54a, 54b, 54c).

28. The spectrometer of claim 27 wherein the adjoining part is another one of the support elements (12 - 24).

29. The spectrometer of any of the preceding claims further comprising at least one electrically controllable actuator (84) arranged between a support element and a neighboring part of the spectrometer.

30. A Raman spectrometer, in particular of any of the preceding claims, comprising a light source (26) emitting light at an excitation wavelength range, a sensing port (30) adapted for passage of light towards and from a target, illumination optics (28a - 28d) comprising at least one illumination lens (28a - 28d) and being adapted to project light from the light source (26) through the sensing port (30) towards a target, a filter assembly (32, 78, 80, 82a, 82b) positioned to receive light returning from the target and adapted to block light in the excitation wavelength range, and collimation optics (34a - 34c) comprising at least one collimation lens (34a, 34b) and being adapted to collimate the light returning from the target, a spectrometer (36) positioned to receive collimated and filtered light after having passed through the collimation optics (34a - 34c) and the filter assembly (32, 78, 80, 82a, 82b). wherein the filter assembly (32, 78, 80, 82a, 82b) comprises a first filter element (32, 78, 82a) arranged between the sensing port (30) and the collimation optics (34a - 34c) and wherein every illumination lens (28a - 28d) is of glass and at least one collimation lens (34a, 34b) is of plastics.

31. The spectrometer of claim 30 wherein every collimation lens (34a, 34b) is of plastics.

32. The spectrometer of any of the claims 30 or 31 wherein the first filter element is a dichroic beam splitter (32).

33. The spectrometer of any of the preceding claims further comprising a bandpass filter (32) for the excitation wavelength range, and in particular wherein the bandpass filter (32) is formed by a beam splitter of the illumination optics.

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