Optical spectrometer and Raman microscope including such a spectrometer

Abstract

An optical spectrometer (10) comprising: an aperture (13) configured to receive a source light beam, a first optical system being configured to receive the source light beam and form a collimated light beam directed towards a diffraction grating, the diffraction grating being configured to receive the collimated light beam and to form a diffracted light beam, a second optical system being configured to form an image of the diffracted light beam on an image sensor. According to the invention, the image sensor is a CMOS sensor having pixels (34) arranged in N lines oriented in a direction inclined at an angle alpha to the spectral diffraction direction of the image of the diffracted light beam, where alpha is less than 10 degrees, N is greater than or equal to 3, each pixel has a height and a width defining an aspect ratio of the pixel greater than two. Figure for abstract: Fig.1

Description

Title of the invention: Optical spectrometer and Raman microscope comprising such a spectrometer Technical field of the invention

[0001] The present invention relates generally to optical spectrometers.

[0002] It relates more particularly to an optical spectrometer comprising an aperture configured to receive a source light beam, a first optical system, a diffraction grating, a second optical system and an image sensor, the first optical system being arranged and configured to receive the source light beam and form a collimated light beam directed towards the diffraction grating, the diffraction grating being positioned so as to receive the collimated light beam and configured to form a diffracted light beam, and the second optical system being arranged and configured to form an image of the diffracted light beam on the image sensor.

[0003] The invention finds a particularly advantageous application in Raman microscopy.

[0004] It also relates to a Raman microscope. State of the art

[0005] In spectrometry, and more specifically in Raman spectrometry, spectral resolution and imaging resolution are key parameters to optimize. Often, spectral resolution is favored to the detriment of imaging resolution, giving rise to spectra spread in height (i.e. in a direction perpendicular to the direction of spectral dispersion) because of an optical aberration called astigmatism.

[0006] The spectrum is then composed of spectral lines generally recorded by a CCD or CMOS type matrix sensor composed of square pixels. The spectral lines therefore spread over several pixels, and the different pixel values are added together to obtain the value of the spectral signal.

[0007] This technique is costly in terms of time (the reading time for several pixels is higher than for one pixel for a CCD sensor) and in terms of noise (for example, for a CMOS sensor, each pixel acquires a reading noise B, the total noise associated with the reading of N pixels is thus B^'^N )•

[0008] Other types of sensors exist, such as CCD sensors comprising a single line of rectangular pixels. These sensors are composed of pixels having a large surface area (making it possible to capture the entire height of the spectrum in one pixel for all wavelengths), generating significant measurement noise because the dark current is proportional to the pixel area. In addition, these sensors do not allow high-performance Raman spectrometry. Indeed, to perform Raman spectrometry, and more specifically Raman microscopy, it may be necessary to image several spectra simultaneously over the height of the detector.

[0009] There is a need for an optical imaging spectrometer providing both good spectral resolution and capable of imaging one or more spectra simultaneously, with reduced measurement noise and limited readout time. Presentation of the invention

[0010] In order to overcome the aforementioned drawbacks of the prior art, the present disclosure relates to an optical spectrometer comprising an aperture configured to receive a source light beam, a first optical system, a planar diffraction grating, a second optical system and an image sensor, the first optical system being arranged and configured to receive the source light beam and form a collimated light beam directed towards the diffraction grating, the diffraction grating being positioned so as to receive the collimated light beam and configured to form a diffracted light beam, and the second optical system being arranged and configured to form an image of the diffracted light beam on the image sensor.

[0011] According to the invention, the image sensor is a CMOS sensor comprising pixels arranged in N lines oriented in a direction inclined at most by an angle alpha relative to the spectral diffraction direction of the image of the diffracted light beam, where the angle alpha is less than 10 degrees, N being an integer greater than or equal to 3, each pixel has a height h and a width w defining a pixel aspect ratio R=h / w, in which the pixels all have the same height h and the same width w and the pixel aspect ratio R is greater than 2.

[0012] The present disclosure proposes the use of a CMOS sensor comprising several lines of rectangular pixels.

[0013] Thus, by using a CMOS sensor, the reading time is reduced. The aspect ratio is adapted to reduce the measurement noise. In addition, the use of at least three lines of pixels allows the spectrometer to be used for imaging applications (for example, Raman microscopy) or for spectropolarimetry applications.

[0014] Preferably, the aspect ratio of the pixel R is less than or equal to 20.

[0015] In an exemplary embodiment, each line of the sensor comprises M pixels, M being between 512 and 4096.

[0016] Advantageously, the pixels are arranged in M columns.

[0017] According to a particular aspect, the image sensor comprises an electronic system configured to collect and sum pixel values from the same column.

[0018] According to one embodiment, the number of lines N is less than or equal to 256, or even 128.

[0019] According to another particular aspect, the height of a pixel h is between 6 micrometers and 300 micrometers and the width w of a pixel is between 2 micrometers and 50 micrometers.

[0020] In one exemplary embodiment, the opening is a rectangular inlet slot having a slot height Hf. In another embodiment, the opening comprises at least one circular or square opening.

[0021] Optionally, the optical spectrometer comprises an optical polarization splitter arranged and configured to separate the diffracted light beam into two polarized beams, the optical spectrometer being configured to simultaneously form an image of each of the two polarized beams on the image sensor and in which the image of one of the two polarized beams is separated from the image of another of the two polarized beams by at least one line of pixels.

[0022] The invention also relates to a Raman microscope comprising an optical spectrometer according to the present disclosure.

[0023] Advantageously, the aperture comprises at least two confocal diaphragms, the optical spectrometer being configured to simultaneously form an image of each of the at least two confocal diaphragms on the image sensor and each image of a confocal diaphragm is separated from another image of another confocal diaphragm by at least one line of pixels.

[0024] Of course, the various features, variants and embodiments of the invention may be combined with each other in various combinations to the extent that they are not incompatible or mutually exclusive. Detailed description of the invention

[0025] The description which follows with reference to the appended drawings, given as non-limiting examples, will make it clear what the invention consists of and how it can be implemented.

[0026] In the attached drawings:

[0027] [Fig.l] is a schematic view of an optical spectrometer according to a first embodiment;

[0028] [Fig.2] is a schematic view of an optical spectrometer according to a second mode of realization;

[0029] [Fig.3] is a schematic view of an optical spectrometer according to a third mode of realization;

[0030] [Fig.4] is a schematic view of the spectrometer detector according to any one embodiments;

[0031] [Fig.5] is a view of an example of a spectrometry image obtained on a spectrometer equipped with a CMOS sensor according to the present disclosure;

[0032] [Fig.6] is a view illustrating, on the left, an aperture comprising three confocal diaphragms and, on the right, the corresponding spectral image obtained on a spectrometer equipped with a CMOS sensor according to the present disclosure; and

[0033] [Fig.7] is a schematic view of a Raman microscope as described by the invention.

[0034] In [Fig. 1], an optical spectrometer 10 according to a first embodiment is shown. The optical spectrometer 10 makes it possible to analyze a light beam coming from a light source 12, which is generally an external light.

[0035] The light source 12 may for example come from one end of a cable comprising several superimposed optical fibers supplying light to the optical spectrometer 10.

[0036] The optical spectrometer 10 comprises a housing 11 with an opening 13 (or a porthole) configured to receive the light beam. The opening 13 may take the form of a rectangular or circular hole, or a slit. The opening 13 has a height Hf in the direction perpendicular to the plane of FIG. 1.

[0037] The light source 12 can be generated from any source comprising parts of the spectrum or the entire spectrum. Depending on the application, the light source 12 here emits light in a discrete or continuous optical spectrum, extending for example from ultraviolet to infrared (260 nm - 2 pm).

[0038] Light from source 12 enters the housing as an input beam 16 that diverges from input point 14 to a first optical system 18. Here, the first optical system 18 is a spherically curvature concave collimating mirror. The first optical system 18 redirects the light as a collimated beam 20, as shown in [Fig.l], onto a diffraction grating 22.

[0039] The diffraction grating 22 is flat and formed of straight, parallel and regularly spaced lines 24. The lines of the diffraction grating 22 are here perpendicular to the plane of fig. 1. The diffraction grating 22 is here reflective, it is positioned to receive and reflect the collimated light beam, and form a diffracted light beam 20 in different directions depending on the different wavelengths present in the spectrum of the light source 12.

[0040] In [Fig.l], schematically, each ray incident on the diffraction grating 22 is dispersed into three rays forming the spectrally diffracted beam. Naturally, the diffraction depends on the light source 12 and is not restricted to three wavelengths. After reflection on the diffraction grating 22, the diffracted beams 26 are collimated. The diffracted beams 26 are directed onto a second optical system 28.

[0041] The second optical system 28 is here a concave focusing mirror. The second optical system 28 focuses the light beams 26 into an output beam 30 which is directed towards an image sensor 32. In other words, the second optical system 28 forms an image of the diffracted beam on the image sensor 32.

[0042] In a second embodiment of the optical spectrometer 10, illustrated in [Fig. 2], the diffraction grating 22 is a grating operating in transmission. In addition, the first optical system 18 is a refractive optical system comprising for example a collimating lens and the second optical system 28 is a refractive optical system comprising for example a lens for focusing the output beam 30 onto the image sensor 32.

[0043] In a third embodiment, illustrated in [Fig. 3], the optical spectrometer 10 is of the Czemy-Turner type. The diffraction grating 22 is a grating operating in reflection. The first optical system 18 is a reflective optical system and the second optical system 28 is also a reflective optical system. This configuration makes it possible to fold the optical paths and obtain a more compact spectrometer.

[0044] Of course, there are other known configurations of optical spectrometers that also fall within the scope of the present disclosure. In particular, the optical spectrometer may be in a non-planar configuration. The optical spectrometer 10 may also comprise several diffraction gratings 22 arranged in series on the path of the light beam so as to increase the spectral dispersion of the light beam.

[0045] As shown in Figures 1-3, each wavelength is focused into a different image spot 31 along the image sensor 32 in the spectral diffraction direction. The spectral diffraction direction is located in a plane perpendicular to the lines of the diffraction grating 22 for an optical spectrometer 10 in a planar configuration. Each image spot 31 is called a spectral line. The size of the image spot 31 on the image sensor 32 for a particular wavelength of light, i.e., perpendicular to the spectral diffraction direction, is dependent on the size of the input spot 14 and the ratios of various geometries of the optical components and their placement in the optical system. The width of the imaged spot in the spectral diffraction direction (which is the same direction as the length of the image sensor 32) determines the spectral resolution of the optical spectrometer 10.The optical design of the optical spectrometer 10 is generally defined to maximize spectral resolution.

[0046] Furthermore, the light beams 16, 20 and 26, 30 being reflected or transmitted by optical systems 18, 28 having curvatures and off-axis, the effective focal length of the optical systems 18, 28 in the "tangential" or "meridional" plane of [Fig.l], 2 or 3 is shorter than the effective focal length of the optical systems in the "sagittal" plane perpendicular to the plane of the drawing. Therefore, when the image point is focused in the tangential plane, it is not perfectly focused in the sagittal plane by the second optical system 28. The light beams 30 then form a line of light of each wavelength on the detector perpendicular to the plane of [Fig.l], rather than a point. This is called astigmatism. A spectrum imaged on an image sensor 32 and including astigmatism is shown in [Fig.6].

[0047] [Fig. 6] shows three source points 15, 17, 19 arranged on the input slit 13 of the optical spectrometer. The source points 15, 17, 19 correspond, for example, to the ends of three optical fibers or to the image of a spatially extended source. Each source point 15, respectively 17, 19 produces a spectrum 55, respectively 57, 59, on the image sensor 32 of an optical spectrometer 10. By way of example, the spectra 55, 57, 59 are here continuous spectra in the spectral domain considered. For each spectrum 55, 57, 59, the widening of the image spot due to astigmatism in a direction transverse to the direction of spectral diffraction, in other words in the direction of the height of the pixels, has been indicated by two dotted lines.

[0048] Astigmatism depends on several parameters including the wavelength. In other words, the height of the aberration and therefore of the image on the sensor depends on the wavelength. For example, we observe in [Fig.6] that the astigmatism is greater at the two ends of each spectrum. We call Hmax the maximum height of the aberration, that is to say of a spectral line, under the conditions of use of the optical spectrometer 10 (in particular the wavelength range, or the orientation of the grating).

[0049] If the beamline is greater than the height of the image sensor 32, the excess light is lost and the sensitivity of the optical spectrometer 10 is reduced. The image sensor 32 is here chosen to have a total height H greater than a threshold value, defined by the maximum height Hmax.

[0050] In [Fig.4], the image sensor 32 is shown schematically. The sensor image sensor 32 here comprises pixels 34 arranged in N lines, where N is an integer. N is greater than or equal to 3. Preferably N is less than or equal to 128. The image sensor 32 has a height H and a width L. For example, the height H and a width L are H=6mm and L=25mm. Typically, the height H is between 1mm and 10mm, and the length L is between 6mm and 30mm.

[0051] The image sensor 32 is arranged such that the pixel lines are oriented in a direction inclined at most by an angle alpha relative to the spectral diffraction direction of the image of the diffracted light beam, where the angle alpha is less than 10 degrees and preferably less than 5 degrees. Advantageously, the 34 pixel lines are oriented parallel to the spectral diffraction direction of the diffracted light beam image, in other words the alpha angle is zero.

[0052] Preferably, each row comprises M pixels 34, M being between 512 and 4096. In addition, the pixels 34 are generally arranged in a column such that the pixels 34 form a matrix on the image sensor 32. Preferably, all the pixels 34 of the image sensor 32 have the same width w and the same height h. For example, the height h of a pixel 34 is between 6 micrometers (pm) and 300 pm, and the width w of a pixel 34 is between 2 pm and 50 pm.

[0053] Each pixel 34 has a height h and a width w defining an aspect ratio of the pixel 34 R=h / w. The aspect ratio of the pixel 34 R is greater than 2.

[0054] The advantage of using such an image sensor 32 is that unlike a conventional detector with square pixels, the aspect ratio of the pixels 34 makes it possible to receive a spectral line 31 on a single pixel 34. The reading noise associated with the spectral measurement then corresponds to the reading noise of a single pixel 34.

[0055] In other words, the large height h of pixel 34 makes it possible to reduce the reading noise by ensuring that the light of a spectral line is measured on a pixel 34 in height despite a significant vertical aberration.

[0056] Alternatively, a spectral line can be measured on two or three pixels of the same column, by summing the intensities detected on these two or three pixels of the same column. The reading noise associated with this sum on two or three pixels always remains low compared to a conventional detector where it is necessary to sum on at least twice as many pixels.

[0057] A spectral line having a spectral width that is more or less fine depending on the line measured and depending on the characteristics of the optical spectrometer 10, it is also provided that a spectral line can be measured on one or more pixels of the same line.

[0058] The image sensor 32 is here a CMOS sensor. The pixel height 34 must not be too large to allow good operating efficiency of the CMOS circuit. The aspect ratio R is here less than 20. The height h of the pixel 34 and the aspect ratio R make it possible to maintain the performance in terms of signal-to-noise ratio of the image sensor 32.

[0059] In addition, CMOS sensor technology makes it possible to chain the acquisition of 2D spectra at a much higher speed than a conventional CCD camera having the same number of pixels 34. In practice, the acquisition of an image on a CCD detector of 2048x2048 pixels 34 takes approximately 4 seconds, while the acquisition of an image on a CMOS detector of the same number of pixels 34 is almost instantaneous, of the order of 20 ms.

[0060] Particularly advantageously, the image sensor 32 comprises a measuring system comprising a column analog-digital converter device parallel (or “Parallel column ADC” in English), that is to say that the image sensor 32 comprises an analog-to-digital converter (called “ADC” from the Anglo-Saxon “Analog to Digital Converter”) per column. Such a device makes it possible to simultaneously read all the M pixels 34 of the same line and to save approximately a factor M in reading time.

[0061] Furthermore, in order to save data processing time, the measurement system can also sum the values of the pixels 34 over a determined portion of several adjacent pixels 34 of the same column.

[0062] Such an image sensor 32 with rectangular pixels 34 with an aspect ratio of between 2 and 20 therefore has improved speed and / or signal-to-noise ratio performance compared to optical spectrometers 10 using matrix sensors with square or low aspect ratio 34 pixels.

[0063] CMOS detectors have a sensitivity that is very comparable to CCD detectors, which themselves have higher electronic noise than photomultiplier (PM) detectors, but a much higher quantum efficiency. In addition, CMOS detectors have a much smaller dynamic range than PM detectors. Finally, CMOS detectors have a lower cost compared to CCD detectors.

[0064] In addition, the arrangement of the pixels 34 in several lines makes it possible to correct thermal or mechanical drifts which can be one of the performance limits of the optical spectrometers 10. For example, in the case of an optical spectrometer 10 using several diffraction gratings, the orientation of the lines (which determines the direction of spectral diffraction), can be different between several gratings, or else evolve over time. It is then advantageous to have several lines of pixels in order to be able to obtain the spectrum by summing pixels 34 according to a profile which is not exactly vertical. For example, a spectral line can be inclined by an angle beta relative to the vertical defined by the columns of the image sensor 32, beta being less than 10 degrees (see [Fig. 6]). This aspect of the invention makes it possible to obtain excellent spectral resolution compared to the use of a sensor with a single line of rectangular pixels 34.

[0065] Furthermore, it is advantageous to parameterize the number p of rectangular pixel lines 34 read and summed to obtain each spectrum, where p is an integer greater than or equal to 1. Indeed, depending on the wavelengths and the configuration of the optical spectrometer 10, the height of the spectrum on the image sensor 32 can vary (see [Fig.6]). It is then of course useful to take into account the entire height of the p pixel lines L5, respectively L7, L9, of the image sensor 32 on which the spectrum 55, respectively 57, 59, is located. It is also advantageous to be able to exclude from this sum the groups of lines L6, L8, L10 of unilluminated pixels 34, above likely to add only read noise. This operation, although similar to that of a conventional 34-square pixel sensor, offers the advantage of using a lower number p of lines than a conventional sensor and therefore of presenting a better signal to noise ratio. Since reading is very fast, a first measurement can possibly select the groups of pixel lines L5, respectively L7, L9, containing the spectral signal.

[0066] The arrangement of the pixels 34 in lines also has the advantage of allowing several spectra to be measured simultaneously on different lines of the image sensor 32, as illustrated in [Fig.6]. This application is particularly advantageous in spectropolarimetry to allow the different polarization components of a beam to be imaged on different lines of pixels. This application also finds applications in Raman microscopy for example, to form the spectral image of different points of the sample to be analyzed on different lines of the optical spectrometer 10.

[0067] [Fig.7] schematically represents a Raman microscope 100 comprising an optical spectrometer 10, for example according to the second embodiment.

[0068] The Raman microscope 100 comprises a laser source 44 which sends a laser beam. The laser beam is reflected by a first mirror 47 then focused on a sample 42 to be studied by a collimating lens 43. The sample 42 is excited by the laser and emits light which passes back through the collimating lens 43, creating a collimated beam.

[0069] The collimated beam is reflected by a second mirror 46 and focused onto the aperture 13 of the optical spectrometer 10. The aperture 13 of the optical spectrometer 10 here comprises, for example, a confocal diaphragm.

[0070] The collimated beam passes through a first optical system 18. The first optical system 18 is here for example a collimation lens, and makes it possible to collimate the light beam after it passes through the opening 13 of the optical spectrometer 10.

[0071] The beam exiting the first optical system 18 passes through a polarization splitter 41 configured to split the beam into two beams of orthogonal polarizations. The beam splitter 41 may, for example, be a Wollaston prism. Alternatively, the beam splitter 41 may be a semi-reflecting plate or a Rochon prism.

[0072] The two polarized and spatially separated beams then pass through the diffraction grating 22. Here, the diffraction grating 22 is a transmission grating. The diffraction grating 22 makes it possible to diffract the polarized beams.

[0073] The diffracted beams are focused onto the image sensor 32 using the second optical system 28 (not shown in [Fig.7] for simplification). The second optical system 28 is here a spherical or weakly toric mirror. The image sensor 32 receives two polarized images from the aperture 13 of the optical spectrometer 10. The two polarized images are formed on separate pixel lines of the image sensor 32.

[0074] In order to be able to separate the two spectra easily, the optical spectrometer 10 is configured so that the two polarized images are separated by at least one line of pixels 34 on the image sensor 32. Preferably, the two polarized images can be separated by three lines of pixels 34 (each spectrum is framed by a line of black pixels 34, i.e. a line of pixels receiving no light flux, to ensure that the entire spectrum is obtained, plus another line of black pixels to be certain of the separation of the spectra). A prior measurement makes it possible to determine the positions of the lines of illuminated pixels and the lines of black pixels, which essentially depend on the optical design and not on the sample considered.

[0075] Optionally, the Raman microscope 100 advantageously comprises a wave plate 48 located before the opening 13 of the optical spectrometer 10 (in the direction of the light) in order to be able to rotate the polarization at the entrance of the optical spectrometer 10.

[0076] [Fig. 5] shows an example of spectral measurement of the sample 42 with the Raman microscope 100 of [Fig. 3]. Two polarized spectra 51, 53 are observed, separated by an empty space 52 corresponding to one or more lines of pixels, for example three lines of pixels. The polarized spectra 51, 53 have the same spectral components but each spectral component does not have the same intensity. Each spectrum 51, 53 is framed by two spaces of black pixels. The first spectrum 51 (the uppermost) is framed by two areas of black pixels 50, 52. The second spectrum 53 (the lowermost) is framed by two areas of black pixels 52, 54.

[0077] Alternatively, the aperture 13 may comprise at least two confocal diaphragms. In this case, at least two beams from the sample 42 are observed simultaneously.

[0078] The optical spectrometer 10 is then configured to image the two confocal diaphragms on the image sensor 32. The two images are separated by at least one pixel line 34, and preferably by three pixel lines 34.

[0079] Similarly, the aperture 13 may comprise more than two confocal diaphragms, for example three, as for example illustrated in [Fig.6]. The reasoning applies in the same way to the number of confocal diaphragms present.

[0080] In the case where the optical spectrometer 10 is used to analyze P separate light spots at the input, the image sensor 32 preferably comprises at least 2P+1 lines of rectangular pixels 34 allowing the spectral images of the P spots to be sufficiently separated so as not to be confused and for each spectral image to be framed by two black lines (a line of black pixels below and a line of black pixels above) to acquire the full height of the spectrum without ambiguity.

[0081] The present invention is in no way limited to the embodiments described and shown, but those skilled in the art will be able to provide any variation in accordance with the present disclosure.

Claims

Claims

1. An optical spectrometer (10) comprising: at least one aperture (13) configured to receive a source light beam, a first optical system (18), a planar diffraction grating (22), a second optical system (28) and an image sensor (32), the first optical system (18) being arranged and configured to receive the source light beam and form a collimated light beam directed towards the diffraction grating (22), the diffraction grating (22) being positioned so as to receive the collimated light beam and configured to form a diffracted light beam, and the second optical system (28) being arranged and configured to form an image of the diffracted light beam on the image sensor (32),characterized in that: the image sensor (32) is a CMOS sensor comprising pixels (34) arranged in N lines oriented in a direction inclined at most by an angle alpha relative to the spectral diffraction direction of the image of the diffracted light beam, where the angle alpha is less than 10 degrees, N being an integer greater than or equal to 3, each pixel (34) has a height h and a width w defining a pixel aspect ratio R=h / w, in which the pixels (34) all have the same height h and the same width w and in which the pixel aspect ratio R is greater than 2 and less than or equal to 20.,

2. An optical spectrometer (10) according to claim 1, wherein each row of the image sensor (32) comprises M pixels, M being between 512 and 4096.

3. An optical spectrometer (10) according to claim 2, wherein the pixels (34) are arranged in M columns.

4. An optical spectrometer (10) according to claim 3, wherein the image sensor (32) comprises an electronic system configured to collect and sum the values of pixels (34) of the same column.

5. Optical spectrometer (10) according to one of claims 1 to 4, in which the number of lines N is less than or equal to 256.

6. An optical spectrometer (10) according to one of claims 1 to 5, wherein the height h of a pixel (34) is between 6 micrometers and 300 micrometers, and wherein the width w of a pixel (34) is between 2 micrometers and 50 micrometers.

7. An optical spectrometer (10) according to one of claims 1 to 6, wherein said at least one opening (13) is a rectangular entrance slit having a slit height (Hf) or wherein said at least one opening (13) comprises at least one circular or square opening.

8. An optical spectrometer (10) according to one of claims 1 to 7, comprising an optical polarization splitter (41) arranged and configured to separate the diffracted light beam into two polarized beams, the optical spectrometer (10) being configured to simultaneously form an image of each of the two polarized beams on the image sensor (32) and wherein the image of one of the two polarized beams is separated from the image of another of the two polarized beams by at least one line of pixels.

9. Raman microscope (100) comprising an optical spectrometer (10) according to one of claims 1 to 8.

10. The Raman microscope (100) of claim 9, wherein said at least one aperture (13) comprises at least two confocal diaphragms (15, 17, 19), wherein the optical spectrometer (10) is configured to simultaneously form an image (55, 57, 59) of each of the at least two confocal diaphragms (15, 17, 19) on the image sensor (32) and wherein each image of a confocal diaphragm is separated from another image of another confocal diaphragm by at least one line of pixels.

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