Spectrometer device with light source and spectral analyzer

Abstract

A spectrometer device comprises at least a first light source (10) emitting light in a first illumination wavelength range and at least a first spectral analyzer (26, 26a) adapted to analyze light in a first analyzer wavelength range. A dichroic first illumination mirror (16, 16a) is provided to reflect light in the illumination wavelength range from the first light source (10) towards a target (12). A dichroic first analyzer mirror (18, 18a) reflects light in the analyzer wavelength range that returns from the target towards the spectral analyzer (26, 26a). The first illumination mirror (16, 16a) is transmissive for light in the first analyzer wavelength range and the first analyzer mirror (18, 18a) is transmissive for light in the first illumination wavelength range. The first illumination mirror (16, 16a) intersects the first analyzer mirror (18, 18a).

Description

[0001] Spectrometer device with light source and spectral analyzer

[0002] Technical Field

[0003] The invention relates to a spectrometer device having a light source for illuminating a target and a spectral analyzer to spectrally analyze light scattered from the target.

[0004] Background Art

[0005] Spectrometer devices may comprise a light source for emitting excitation light into a sample and a spectral analyzer for analyzing the spectral composition of light returning from the sample. Such devices are, e.g., suitable for performing Raman spectroscopy and / or fluorescence spectroscopy.

[0006] R. Smith et al., "Raman spectroscopy: an evolving technique for live cell studies", Analyst, 2016, 141, 3590-3600, DOI: 10.1039 / c6an00152a describes such a spectrometer device using a dichroic mirror for reflecting light from a light source towards a target. The returning light from the target passes the mirror and is sent to a spectral analyzer.

[0007] This type of device is bulky and poorly suited for applications with strong spatial constraints, such as for applications in wearable or implantable devices.

[0008] Disclosure of the Invention

[0009] The problem to be solved by the present invention is to provide a spectrometer device with a design suited for applications with strong spatial constraints.

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

[0011] Accordingly, the spectrometer device comprises at least the following elements:

[0012] - At least a first light source adapted to emit light in a first illumination wavelength range: This light may be used as excitation light to be sent to the target. - At least a first spectral analyzer adapted to analyze light in a first analyzer wavelength range: The spectral analyzer may be used to spectrally analyze the light returning from the target.

[0013] - At least a dichroic first illumination mirror adapted to reflect light in the illumination wavelength range from the first light source towards the target.

[0014] - At least a dichroic first analyzer mirror adapted to reflect light in the analyzer wavelength range from the target towards the spectral analyzer.

[0015] The first illumination mirror is transmissive for light in the first analyzer wavelength range and the first analyzer mirror is transmissive for light in the first illumination wavelength range. Further, the first illumination mirror intersects the first analyzer mirror.

[0016] This design is based on the understanding that separate dichroic mirrors may be used for the excitation light and for the light returning from the target. One of them reflects the excitation light and the other reflects the light to be analyzed. This allows for a flexible placement of the light source and the spectral analyzer, taking into account the spatial requirements of a given application.

[0017] The (at least) two mirrors intersect, i.e., they can be arranged in substantially the same location, which again makes the design of the device more compact. However, such an overlap is only possible because the illumination mirror is transmissive for light in the first analyzer wavelength range and the analyzer mirror is transmissive for light in the first illumination wavelength range, thereby preventing the illumination mirror from shadowing the light returning from the target and preventing the analyzer mirror from shadowing the light from the light source.

[0018] In this context, "transmissive for light in a... wavelength range" may, in particular, be understood such that the respective mirror transmits at least 50%, in particular at least 75%, of the light in said wavelength range.

[0019] The spectrometer device may further comprise:

[0020] - A sensing port: The illumination mirror(s) is adapted to reflect light from the light source(s) through the sensing port, and the analyzer mirror(s) is adapted to reflect light from the sensing port towards the spectral analyzer(s). Hence, the sensing port may be used as an opening or window that forms an optical interface between the spectrometer device and the target.

[0021] - Focusing optics arranged between the sensing port and the mirrors.

[0022] In this case, the same optics may be used to focus the excitation light towards the sensing port (and therefore the target) and to pick up and process (e.g., substantially collimate) the returning light. This again helps to make the device more compact.

[0023] The device may have more than one light source, with the light sources operating at different illumination wavelength ranges, and with an illumination mirror attributed to each light source. Alternatively or in addition thereto, the device may have more than one spectral analyzer, with the spectral analyzers optionally operating a different analyzer wavelength ranges, and with an analyzer mirror attributed to each spectral analyzer.

[0024] The spectrometer device may, e.g., be used to perform Raman spectroscopy and / or fluorescence spectroscopy on the target, but, as mentioned below, it may also be used for other types of spectroscopic investigations.

[0025] Brief Description of the Drawings

[0026] 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:

[0027] Fig. 1 shows a sectional view of an embodiment of a spectrometer device with one light source and one spectral analyzer,

[0028] Fig. 2 is a schematic view of a spectrometer device with one light source and one spectral analyzer,

[0029] Fig. 3 illustrates embodiments of a mirror assembly for the device of Fig. 2,

[0030] Fig. 4 is another schematic view of a spectrometer device with one light source and one spectral analyzer,

[0031] Fig. 5 illustrates embodiments of a mirror assembly for the device of Fig. 4,

[0032] Fig. 6 is a schematic view of a spectrometer device with two light sources and one spectral analyzer,

[0033] Fig. 7 illustrates embodiments of a mirror assembly for the device of Fig. 6,

[0034] Fig. 8 is a schematic view of a spectrometer device with two light sources and two spectral analyzers,

[0035] Fig. 9 illustrates embodiments of a mirror assembly for the device of Fig. 8, Fig. 10 illustrates another type of embodiments of the mirror assembly,

[0036] Fig. 11 illustrates yet another type of embodiments of the mirror assembly,

[0037] Fig. 12 illustrates embodiments of the mirror assembly with mirror plates,

[0038] Fig. 13 illustrates a type of embodiments of the mirror assembly having triangular cross section and two mirrors, and

[0039] Fig. 14 illustrates a type of embodiments of the mirror assembly having triangular cross section and three mirrors.

[0040] Modes for Carrying Out the Invention

[0041] Definitions

[0042] The term "transversal" is to be understood as "non-parallel".

[0043] A plane is "tilted" in respect to a direction if the plane is neither parallel nor perpendicular to the direction.

[0044] The "vector" of a propagating light field (e.g., propagating from the light source towards the illumination mirror or from the analyzer mirror towards the spectral analyzer) is to be understood as the weighted average of the direction vectors of the planar light waves in the light field weighted by the intensity of said light planar light waves.

[0045] The "angle" between two vectors a, b is given by cos-1((a b) / (|a| |b|)), i.e., it is a quantity between 0° and 180°.

[0046] The "angle" between two intersecting planes, such as between two mirrors, is the smaller of the two angles between them, i.e., it is a quantity larger 0° and up to 90°.

[0047] Two mirrors "intersect" if they are non-parallel and intersect along a line of intersection.

[0048] A "dichroic mirror" is a mirror whose reflectance and transmission are different functions of the wavelength such that they reflect light in at least one spectral range while they transmit light at least in one other spectral range. The term also includes trichroic mirrors or multichroic mirrors. Example Design

[0049] Fig. 1 illustrates the design of some embodiments of a spectrometer device, such as it can, e.g., be used for Raman spectroscopy or other types of spectroscopy.

[0050] The shown device may comprise functional sections including an illumination section 2, a mirror section 4 with a mirror assembly 5, a probing section 6, and a spectral analyzer 8.

[0051] Illumination section 2 comprises a light source 10 generating light in an illumination wavelength range, and it is adapted to feed this light to mirror assembly 5. Mirror assembly 5 has at least a first illumination mirror 16 that reflects the light from illumination section 2 into probing section 6. Probing section 6 sends the illumination light to a target 12. Light returning from target 12 is collected by probing section 6 and sent back into mirror assembly 5. Mirror assembly 5 further comprises at least a first analyzer mirror 18 reflecting light in an analyzer wavelength range into analyzer 8. Analyzer 8 is adapted to analyze the optical spectrum of the light in the analyzer wavelength range.

[0052] As explained in more detail below, the device may comprise several illumination sections 2 (and light sources) and / or several analyzers 8, which are, e.g., designated as "first" or "second" illumination sections with respective "first" or "second" light sources and "first" or "second" analyzers. Unless specifically mentioned, any reference to a light source, analyzer, etc., designates properties of any of these light sources and analyzers and their attributed mirrors, respectively.

[0053] The following sections briefly describe examples of the light flow as it propagates along the device and the spectral analyzer. Then, examples of the mirror assembly 5 and the device geometry are described in more detail.

[0054] Light Flow

[0055] As mentioned, (each) illumination section 2 comprises a light source 10 that generates light in an illumination wavelength range.

[0056] The illumination wavelength range may be centered around a center excitation wavelength Ao and have a full-width-half-maximum range AA.

[0057] For Raman spectroscopy, AA may be small for good resolution, such as smaller than 5 nm or even smaller than 1 nm.

[0058] Ao depends on the application. 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 ').

[0059] In another example, o 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 ' ).

[0060] Other values of Ao may, e.g., be 795, 808, 830, or 850 nm because lasers are, e.g., available for these wavelengths.

[0061] A typical range of Ao may be between 750 and 880 nm.

[0062] 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.

[0063] Light source 10 may, e.g., be a vertical -cavity surface-emitting laser (VCSEL) for its compact size, narrow bandwidth, mass-production capabilities, and large light power.

[0064] Illumination section 2 further comprises an illumination collimator 14, which is arranged between light source 10 and illumination mirror 16. It is adapted to collimate the light from light source 10 and send it towards mirror assembly 5.

[0065] In Fig. 1, illumination collimator 14 comprises two lenses 14a, 14b, even though other embodiments may have a single lens only or more than two lenses.

[0066] The light from light source 10 travels along a first illumination vector vij as it arrives at illumination mirror 16.

[0067] Illumination mirror 16 reflects the light from light source 10 along a probing vector vp and into probing section 6.

[0068] Probing section 6 comprises focusing optics 20 arranged between mirror assembly 5 and a probing port 22.

[0069] Focusing optics 20 is adapted to focus the substantially collimated light from illumination mirror 16 at probing port 22. In Fig. 1, focusing optics 20 comprises two lenses 20a, 20b, even though other embodiments may have a single lens only or more than two lenses.

[0070] Probing port 22 may be an opening or window at the periphery of the spectrometer device transmissive for light in the illumination wavelength range(s) and the analyzer wavelength range(s). In operation, probing port 22 may, e.g., be placed adjacent to target 12. As a response to the excitation light sent into target 12, target 12 generates returning light, such as Raman-scattered light or fluorescent light. This light lies, at least partially, within the analyzer wavelength range of the spectral analyzer(s) 8.

[0071] The returning light is picked up by probing section 6, is, at least partially, collimated by focusing optics 20, and is sent back to mirror assembly 5.

[0072] The returning light travels opposite to probing vector vp and arrives at analyzer mirror 18, which reflects the light in the analyzer wavelength to travel along a first analyzer vector va | towards the spectral analyzer 8.

[0073] Spectral Analyzer

[0074] In some embodiments, as shown in Fig. 1, the at least one spectral analyzer 8 comprises an analyzer collimator 22.

[0075] Analyzer collimator 22 may, e.g., include collimation optics 24a - 24c, with 24a, 24b being convex lenses and 24c being a pinhole. The distances between pinhole 24c and each lens 24a and 24b are equal to the focal lengths of the lenses 24a, 24b, respectively.

[0076] Analyzer collimator 22 is adapted to improve the collimation of the light scattered back from target 12.

[0077] Spectral analyzer 8 further comprises an analyzer section 26 adapted to spectrally analyze the light in the analyzer wavelength range. This range may, e.g., lie somewhere within Xo and Ao + 200 nm (with Xo 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.

[0078] In a typical example, the spectral analyzation wavelength range may be between 239 cm1and 2213

[0079] Depending on the application, other analyzation wavelength ranges may be used.

[0080] Analyzer section 26 may be 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), https: / / doi.org / 10.1051 / epjconf / 202023812018. For further references, see US5059027A or US10908023B2. The spatial heterodyne spectrometer comprises a spectrometer beam splitter 30 and two gratings 32a, 32b. The spectrometer beam splitter 30 and the gratings 32a, 32b form a Michelson interferometer with two arms 34a, 34b.

[0081] The light enters through an entry side surface 30a of spectrometer beam splitter 30. In the beam splitter, the light is split equally between the two arms 34a, 34b. Beam splitter 30 may be achromatic over the spectral analyzation range. At the end of each arm 34a, 34b, the light is diffracted at the grating 32a and 32b respectively.

[0082] The diffracted components from the gratings 32a, 32b travel back along the arms 34a, 34b. In beam splitter 30, half of their intensity is directed towards an exit 30b of beam splitter 30.

[0083] The diffracted components may pass optional camera optics (not shown) and arrive at a camera 36, where they generate interference patterns.

[0084] The interference patterns of the different pairs of diffracted components of equal wavelength have different spatial frequencies along camera 36.

[0085] Spectral analysis of the spatial spectral components in the image recorded by camera 36 therefore allows to determine the spectral components of the light arriving in spatial heterodyne analyzer section 26.

[0086] The images recorded by camera 36 are processed by a computing device (not shown), which determines the spectrum of the light arriving at spatial heterodyne analyzer section 26.

[0087] In the shown embodiments, analyzer section 26 comprises, in each arm 34a, 34b, a field widening prism 38a, 38b as, e.g., described in US10908023B2 Analyzer section 26 may comprise a spectrometer support 40 that holds spectrometer beam splitter 30, the elements in the arms 34a, 34b, and camera 36 in place.

[0088] While Fig. 1 shows analyzer section 26 to be an SHS analyzer, which is a compact and robust type of analyzer with a good resolution. However, other types of spectral analyzers may be used, too, such as, e.g., prism-based spectrometers, where the light is refracted into spectral components, or normal diffractive grating spectrometers, where, e.g., the light is diffracted into its spectral components at a single grating.

[0089] Mirror Assembly

[0090] Mirror assembly 5 comprises, as mentioned at least one illumination mirror 16 and at least one analyzer mirror 18. Both these mirror types are dichroic mirrors, i.e., they reflect light in at least one spectral range while they transmit light at least in one other spectral range.

[0091] In the shown embodiment, the mirrors are flat, which makes it easier to optimize their spectral reflection and transmission properties in the substantially collimated light fields.

[0092] Some general concepts are now described with reference to Figs. 2 and 3. Fig. 2 schematically illustrates a three-dimensional arrangement of the illumination section 2, mirror section 4, probing section 6, and analyzer 8. Fig. 3 illustrates an embodiment of a mirror assembly 5 for the device of Fig. 2.

[0093] As can be seen from Fig. 3, the light from light source 10 travels along the direction of illumination vector vi | as it arrives at illumination mirror 16. The illumination mirror 16 is adapted to reflect the light from light source 10 arriving along illumination vector vij into the direction of probing vector vp. The analyzer mirror 18, on the other hand, is adapted to reflect the returning light from target 12 travelling against the direction of probing vector vp into the direction along the analyzer vector vaj.

[0094] Hence, on its path to target 12, the light from light source 10 has to cross analyzer mirror 18 once. Similarly, the returning light (from target 12) on its way to spectral analyzer 8 has to cross illumination mirror 16 once.

[0095] Hence, analyzer mirror 18 should be transmissive for light in the illumination wavelength range, and illumination mirror 16 should be transmissive for light in the analyzer wavelength range.

[0096] Fig. 3 illustrates that illumination mirror 16 and analyzer mirror 18 intersect, which allows to mount them in the same volume of space, thereby providing a compact design. It also allows to arrange illumination section 2 and analyzer 8 in a common plane extending transversally to probing vector vp, which allows to reduce the device extension along probing vector vp.

[0097] In the embodiments of Fig. 2 and 3, illumination vector vi^ and analyzer vector va | both extend transversally to probing vector vp, a geometry enabled by having separate illumination and analyzer mirrors.

[0098] For a very compact design, the angles between the probing vector vp and the illumination vector vi | as well as an angle between the probing vector vp and the analyzer vector va^ are both approximately equal to 90°, i.e., between 70° and 110°. This allows to shorten the extension of the spectrometer device along the direction of probing vector vp, e.g., for mounting the device in the flat housing of a wearable device. Mirror Assembly with Linear Geometry

[0099] In Figs. 2 and 3, the illumination vector vi^ and analyzer vector va^ are substantially collinear, i.e., the angle between them is about 180°, i.e., at least 160°, which allows for a narrow design of the spectrometer device in directions perpendicular to these vectors.

[0100] To achieve a substantially collinear arrangement of the illumination vector vi | and analyzer vector va^, the angle a between the illumination mirror 16 and analyzer mirror 18 is substantially 90°, i.e., at least 80°.

[0101] Mirror Assembly with Angled Geometry

[0102] Figs. 4 and 5 illustrate an example of a mirror assembly 5 for a device with angled geometry. Here, the illumination vector vi | and analyzer vector va | are not collinear, with the angle between them being smaller than 160°. In the shown example, the angle between the illumination vector vi^ and analyzer vector va^ is approximately equal to 90°, i.e., between 70° and 110°. This allows to reduce the linear extension of the spectrometer device.

[0103] However, the illumination vector vi | and analyzer vector va | may still both extend along an angle of approximately 90° to the probing vector vp.

[0104] To enable such a geometry, the angle a between the illumination mirror 16 and analyzer mirror 18 is substantially 60°, in particular between 45° and 75°.

[0105] Hence, in more general terms, to accommodate for angled or linear geometry, the angle a between the illumination mirror 16 and analyzer mirror 18 may be between 45° and 90°. Smaller (but non-zero) angles may be possible, though, if light source(s) and / or spectral analyzer(s) are to be placed very close to each other.

[0106] Similarly, to accommodate for angled or linear geometry, the angle between the illumination vector vi^ and the analyzer vector va^ may be between 45° and 180°, in particular between 70° and 180°. Again, smaller (non-zero) angles may be possible, though, if light source(s) and / or spectral analyzer(s) are to be placed very close to each other.

[0107] Mirror Assembly with More Than Two Mirrors

[0108] Mirror assembly 5 may comprise more than two dichroic mirrors. For example, it may comprise two or more intersecting illumination mirrors to receive excitation light from two or more light sources located at different locations, and / or it may comprise two or more analyzer mirrors to send light to two or more analyzers located at different locations.

[0109] Some examples of such embodiments are described in the following.

[0110] The examples of Figs. 6 and 7 show a spectrometer device having two illumination sections 2a, 2b and, therefore, two light sources 10a, 10b. A first one of the light sources, light source 10a, emits light in a first illumination wavelength range, and the second one of the light sources, light source 10b, emits light in a second illumination wavelength range. The two illumination wavelength ranges may, e.g., differ in that their central wavelengths differ by at least the smaller of their respective spectral half-widths.

[0111] Two or more different light sources at different illumination wavelength ranges may, e.g., be used to probe different resonances, vibrations, or absorption bands of the target. The two light sources may be operated sequentially, or, e.g., for probing multi-photon-interactions in target 12, simultaneously.

[0112] Each of the light sources has its own illumination mirror 16a, 16b, i.e., mirror assembly 5 comprises

[0113] - a dichroic first illumination mirror 16a adapted to reflect light in the first illumination wavelength range arriving along a first illumination vector vi | into the direction of probing vector vp, and

[0114] - a dichroic second illumination mirror 16b adapted to reflect light in the second illumination wavelength range arriving along a second illumination vector vi2 into the direction of probing vector vp.

[0115] In the example of Figs. 6 and 7, mirror assembly 5 further comprises at least a first dichroic analyzer mirror 18 similar to the embodiment of Figs. 4, 5.

[0116] In order to avoid undesired interactions between the mirrors and the light fields, the transmission of the mirrors may be selected as follows:

[0117] - the first illumination mirror 16a is transmissive for light in the second illumination wavelength range and the analyzer wavelength range,

[0118] - the second illumination mirror 16b is transmissive for light in the first illumination wavelength range and the analyzer wavelength range,

[0119] - the analyzer mirror(s) 18 is / are transmissive for light in the first and second illumination wavelength ranges.

[0120] In order to send and receive light along different directions, the second illumination mirror 16b intersects both the first illumination mirror 16a and the analyzer mirror 18, i.e., all three (or more) mirrors 16a, 16b, 18 intersect. For a flat design of the spectrometer device along the direction of the probing vector vp, all of the following conditions may be fulfilled:

[0121] - the angle between the probing vector vp and the first illumination vector vij,

[0122] - the angle between the probing vector vp and the second illumination vector vift, and

[0123] - the angle between the probing vector vp and the analyzer vector vai are between 70° and 110°.

[0124] In this case, the vectors vij, vi2, and va | and the respective components 2a, 2b, 8 may be arranged substantially in a plane perpendicular to probing vector vp.

[0125] In order to have ample room for both illumination assemblies 2a, 2b, the angle between the first illumination vector vi | and the second illumination vector vi2 may be between 45° an 180°, in particular between 70° and 180°.

[0126] In addition to, or alternatively to, having several light sources and illumination mirrors, the spectrometer device may comprise several spectral analyzers and several analyzer mirrors.

[0127] The examples of Figs. 8 and 9 show a spectrometer device having two analyzer sections 2a, 2b, and therefore two spectral analyzers. A first one of the spectral analyzers is adapted to analyze light in a first analyzer wavelength range, and the second one of the spectral analyzers 26a, 26b is adapted to analyze light in a second analyzer wavelength range. The two analyzer wavelength ranges may, e.g., differ in that their central wavelengths differ by at least the smaller of their respective spectral half-widths.

[0128] In addition, the embodiment of Figs. 8, and 9 comprises two light sources, as the embodiment of Figs., 6, 7, but it may also comprise, e.g., only a single light source as the embodiment of Figs, 4, 5 or 2, 3.

[0129] Each of the spectral analyzers 26a, 26b has its own analyzer mirror 18a, 18b, i.e., mirror assembly 5 comprises

[0130] - a dichroic first analyzer mirror 18a adapted to reflect light in the first analyzer wavelength range arriving along the direction opposite probing vector vp from the target 12 into a direction along a first analyzer vector va | towards the first spectral analyzer 26a, and

[0131] - a dichroic second analyzer mirror 18b adapted to reflect light in the second analyzer wavelength range arriving along the direction opposite probing vector vp from the target 12 along a second analyzer vector va2 towards the second spectral analyzer 26b.

[0132] In the example of Figs. 6 and 7, mirror assembly 5 further comprises a dichroic first illumination mirror 16a and a dichroic second illumination mirror 16b similar to the embodiment of Figs. 6, 7.

[0133] In order to avoid undesired interactions between the mirrors and the light fields, the transmission of the mirrors may be selected as follows:

[0134] - the first analyzer mirror 18a is transmissive for light in the second analyzer wavelength range, the first illumination wavelength range, and (if there are two light sources) the second illumination wavelength range,

[0135] - the second analyzer mirror (18b) is transmissive for light in the first analyzer wavelength range, the first illumination wavelength range, and (if there are two light sources) the second illumination wavelength range,

[0136] - the illumination mirror (16) is transmissive for light in the first and second analyzer wavelength ranges,

[0137] In order to send and receive light along different directions, the second analyzer mirror 18b intersects the first analyzer mirror 18a, the first illumination mirror 16a, and (if present) the second illumination mirror 16b, i.e., all three or four mirrors 16a, 16b, 18a, 18b intersect.

[0138] For a flat design of the spectrometer device along the direction of the probing vector vp, all of the following conditions may be fulfilled:

[0139] - the angle between the probing vector vp and the first analyzer vector va^,

[0140] - the angle between the probing vector vp and the second analyzer vector va2, and

[0141] - the angle between the probing vector vp and the illumination vectors) vi | (or vij, vi2) are between 70° and 110°.

[0142] In this case, the vectors va^, va2, and vi | (or vij, vi2) and the respective components 8a, 8b, 2 (or 2a, 2b) may be arranged substantially in a plane perpendicular to probing vector vp.

[0143] In order to have ample room for both spectral analyzers 26a, 26b, the angle between the first analyzer vector va | and the analyzer illumination vector va2 may be between 70° an 180°. Mechanical and Optical Mirror Assembly Design

[0144] In the embodiments of Figs. 1, 3, 5, 7, and 9, mirror assembly 5 comprises several polyhedral bodies, such as the bodies 42a, 42b, 42c, 42d shown in Figs. 3 or 5, with the mirrors 16, 18 being formed by coatings on the surfaces of the bodies.

[0145] The bodies are of one or more materials transparent in the illumination wavelength range(s) and the analyzer wavelength range(s).

[0146] This design helps to make the mirror assembly 5 robust and compact.

[0147] In the embodiments of Figs. 1, 3, 5, 7, and 9, the polyhedral bodies together form a convex shape, namely a cuboid. It must be noted, though, that no light is entering the topmost part of this shape. Hence, the body in that location may be omitted. This is illustrated in Figs. 10 and 11, which show the embodiments of Figs. 3 and 5 with the topmost body 42d omitted.

[0148] As shown, the polyhedral bodies may have several flat surfaces that are neither parallel nor perpendicular to each other. In the example of Fig. 3, for example, the polyhedral bodies are pyramids with a triangular base. In the embodiment of Fig. 5, two of the polyhedral bodies (bodies 42a, 42b) each have triangular surfaces only and two others (bodies 42c, 42d) have one rectangular surface and two triangular surfaces.

[0149] Instead of using polyhedral bodies assembled into a bulk mirror assembly, the mirrors 16, 18 may, e.g., also be formed by mirror plates 44a, 44b, 44c, 44d as illustrated in Fig. 12. In the shown embodiment, there are four such mirror plates 44a, 44b, 44c, 44d assembled into a cross shape and held by one or more holders 46.

[0150] The bodies 42a - 42d or plates 44a - 44d may be formed of glass to reduce Raman scattering when traversed by the potentially strong light from light source 10. They may, however, also be formed of plastics.

[0151] The mirrors may be formed, as mentioned, by coatings on the surfaces of the bodies or plates. Typically, multi-layer dielectric coatings are used to tune the reflection and transmission at the desired wavelength ranges. Conventional calculation tools may be used to design such coatings, such as RP Coating by RP Photonics AG, Switzerland or the Ray Optics Module by Comsol Inc., Burlington (USA). Non-Rectangular Geometries

[0152] As mentioned above, the angles between the illumination vector(s), probe vector, and analyzer vector(s) may be, approximately, integer multiples of 90°. Small deviations from strict 90° angles may allow to optimize for space constraints or to reduce undesired back-reflections.

[0153] However, other angles may be used as well, in particular between the illumination vector(s) vij and the analyzer vector(s) vap

[0154] An example is shown in Fig. 13. Here, the angle between illumination vector vii and analyzer vector va^ is approximately 120° (e.g., 100° - 140°).

[0155] Another example is shown in Fig. 14 with two analyzer mirrors 18a, 18b splitting the light into two analyzer vectors va^, va2- Here, the angles between the illumination vector vi^ and analyzer vectors va^, va2 are also approximately 120° (e.g., 100° - 140°).

[0156] A design similar to Fig. 14 (with one of the analyzer mirrors 18a, 18b replaced by a second illumination mirror 18b) may be used for a device with two light sources and one analyzer, again with angles between the illumination vectors vij, vi2 and analyzer vector va | being approximately 120° (e.g., 100° - 140°).

[0157] In other designs, in particular if the total number of light sources and analyzers exceeds four, the angles between these vectors may also be less than 90°, e.g., approximately 60° (e.g., 45° - 75°).

[0158] However, as mentioned above, for a compact design along the probing vector vp, the illumination vector(s) vij and the analyzer vectors vaj may extend transversally to the probing vector vp. For example, the angle(s) between the probing vector vp and the illumination vector(s) vij as well as the angle(s) between the probing vector vp and the analyzer vector(s) vaj may be between 70° and 110°.

[0159] Notes

[0160] As shown in Fig. 1, mirror assembly 5 may be housed in a mirror housing 48 of mirror section 4. For a compact, robust design, the illumination section 2 and the analyzer 8 may be mounted to mirror housing 48.

[0161] Hence, in some embodiments, the spectrometer device may comprise

[0162] - a mirror housing 48, wherein the illumination and analyzer mirrors 16, 16a, 16b, 18, 18a, 18b are arranged in the mirror housing, and

[0163] - an illumination section 2, wherein the light source 10 is arranged in the illumination section, wherein the illumination section 2 and the spectral analyzer 8 are mounted to the mirror housing.

[0164] As mentioned, the spectrometer device may comprise

[0165] - an illumination collimator 14 adapted to collimate the light from light source 10 at illumination mirror 16 and

[0166] - a focusing optics 20 adapted to focus the light from illumination mirror 16 towards the target 12 and to collimate the light from the target 12 towards the analyzer mirror 18.

[0167] This design provides for substantially collimated light at the location of the mirrors, thereby making it easier to design them to fulfill the spectral requirements of transmission and reflection as mentioned above.

[0168] This focusing optics may form part of a probe section 6 mounted to the mirror housing 48.

[0169] If several light sources 10 are provided, there may be an illumination collimator 14 for each one of them.

[0170] 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 spectrometer device comprising at least a first light source (10, 10a) emitting light in a first illumination wavelength range, at least a first spectral analyzer (26, 26a) adapted to analyze light in a first analyzer wavelength range, at least a dichroic first illumination mirror (16, 16a) adapted to reflect light in the illumination wavelength range from the first light source (10, 10a) towards a target, at least a dichroic first analyzer mirror (18, 18a) adapted to reflect returning light in the analyzer wavelength range from the target towards the spectral analyzer (26, 26a), wherein the first illumination mirror (16, 16a) is transmissive for light in the first analyzer wavelength range and the first analyzer mirror (18, 18a) is transmissive for light in the first illumination wavelength range, and wherein the first illumination mirror (16, 16a) intersects the analyzer mirror (18, 18a).

2. The spectrometer device of claim 1 further comprising a sensing port (22), wherein the illumination mirror (16, 16a) is adapted to reflect light from the first light source (10, 10a) through the sensing port (22) and wherein the first analyzer mirror (18, 18a) is adapted to reflect light from the sensing port (22) towards the spectral analyzer (26, 26a), and focusing optics (20) arranged between the sensing port (22) and the mirrors.

3. The spectrometer device of any of the preceding claims wherein an angle a between the first illumination mirror (16, 16a) and the first analyzer mirror (18, 18a) is 45° - 90°.

4. The spectrometer device of claim 3 wherein the angle a between the first illumination mirror (16, 16a) and the analyzer mirror (18, 18a) is one of at least 80° or45° - 75°.

5. The spectrometer device of any of the preceding claims wherein the first illumination mirror (16, 16a) is adapted to reflect the light from the first light source (10, 10a) arriving along a first illumination vector (vi | ) into a direction along a probing vector (vp) and the first analyzer mirror (18, 18a) is adapted to reflect the returning light travelling opposite the probing vector (vp) into a direction along a first analyzer vector (va | ) towards the first spectral analyzer (26, 26a), wherein both the illumination vector (vi | ) and the first analyzer vector (va | ) extend transversally to the probing vector (vp).

6. The spectrometer device of claim 5 wherein an angle between the probing vector (vp) and the first illumination vector (vi^) as well as an angle between the probing vector (vp) and the first analyzer vector (va^) are between 70° and 110°.

7. The spectrometer device of any of the claims 5 or 6 wherein an angle 16. an angle between the first illumination vector (vi | ) and the first analyzer vector (vai) is between 45° and 180°, in particular at least 160°.

8. The spectrometer device of any of the preceding claims further comprising an illumination collimator (14) arranged between each light source (10, 10a, 10b) and the illumination mirror (16, 16a, 16b) of the light source (10, 10a, 10b).

9. The spectrometer device of any of the preceding claims comprising a mirror assembly (5) with several adjacent polyhedral bodies (42a - 42d) of material transparent in the illumination wavelength range(s) and the analyzer wavelength range(s), wherein the illumination mirror or mirrors (16, 16a) and the analyzer mirror or mirrors (18, 18a) are formed by coatings on surfaces of the polyhedral bodies (42a - 42d).

10. The spectrometer device of any of the preceding claims further comprising at least a second light source (10b) emitting light in a second illumination wavelength range and at least a dichroic second illumination mirror (16b) adapted to reflect light in the second illumination wavelength range from the second light source (10b) towards the target, wherein- the first illumination mirror (16a) is transmissive for light in the second illumination wavelength range and the analyzer wavelength range,- the second illumination mirror (16b) is transmissive for light in the first illumination wavelength range and the analyzer wavelength range,- the first analyzer mirror (18, 18a) is transmissive for light in the first and second illumination wavelength ranges, wherein the second illumination mirror (16b) intersects both the first illumination mirror (16a) and the analyzer mirror (18, 18a).

11. The spectrometer device of any of the claims 5 to 7 and of claim 10 wherein the second illumination mirror (16b) is adapted to reflect the light from the second light source (10b) arriving along a second illumination vector (vi2) into a direction along the probing vector (vp), and wherein all of the first illumination vector (vi^), the second illumination vector (vi2), and the first analyzer vector (va | ) extend transversally to the probing vector (vp).

12. The spectrometer device of claim 11 wherein all of- an angle between the probing vector (vp) and the first illumination vector (vii),- an angle between the probing vector (vp) and the second illumination vector (vi2), and- an angle between the probing vector (vp) and the first analyzer vector (va | ) are between 45° and 110°.

13. The spectrometer device of any of the claims 11 or 12 wherein an angle between the first illumination vector (vi | ) and the second illumination vector (vi2) is between 45° an 180°, in particular between 60° and 180°.

14. The spectrometer device of any of the preceding claims further comprising at least a second spectral analyzer (26b) adapted to analyze light in a second analyzer wavelength range and at least a dichroic second analyzer mirror (18b) adapted to reflect light in the second analyzer wavelength range from the target towards second analyzer (26b),wherein- the first analyzer mirror (18a) is transmissive for light in the second analyzer wavelength range and the illumination wavelength range(s),- the second analyzer mirror (18b) is transmissive for light in the first analyzer wavelength range and the illumination wavelength range(s),- the first illumination mirror (16, 16a) is transmissive for light in the first and second analyzer wavelength ranges, wherein the second analyzer mirror (18b) intersects both the first illumination mirror (18a) and the analyzer mirror(s) (16).

15. The spectrometer device of any of the claims 5 - 7 or 10 - 13 and of claim 14 wherein the second analyzer mirror (18b) is adapted to reflect the returning light travelling opposite the probing vector (vp) into a direction along a second analyzer vector (va2) towards the second spectral analyzer (26b), and wherein all of the illumination vector (vi^), the first analyzer vector (vai), and the second analyzer vector (va2) extend transversally to the probing vector (vp)16. The spectrometer device of claim 15 wherein all of- an angle between the probing vector and the first illumination vector (vii),- an angle between the probing vector (vp) and the first analyzer vector (vai), and- an angle between the probing vector (vp) and the second analyzer vector (va2) are between 70° and 110°.

17. The spectrometer device of any of the claims 15 or 16 wherein an angle between the first analyzer vector (v | ) and the second analyzer vector (va2) is between 70° and 180°.

18. The spectrometer of any of the preceding claims comprising a mirror housing (48), wherein the illumination and analyzer mirrors (16, 16a, 16b, 18, 18a, 18b) are arranged in the mirror housing (48) and at least one illumination section (2), wherein the light source(s) (10, 10a, 10b) is / are arranged in the illumination section (2),wherein the illumination section(s) (2) and the analyzer(s) (8) are mounted to the mirror housing (48).

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