A Raman spectroscopy and lunar dust velocity measurement combined detection system

Abstract

The present invention relates to an optical detection system, and in particular to a Raman spectrum and lunar dust velocity measurement combined detection system, which solves the technical problem that there is no application report of Raman spectrum in-situ detection in deep space environment in the existing lunar surface in-situ detection payload device, and there is no combined detection of mineral Raman spectrometer and lunar surface dust detection device. The Raman spectrum and lunar dust velocity measurement combined detection system comprises a volume holographic grating spectrometer module, a laser, and a focusing mirror, a dust particle scattered light imaging module and a first condenser arranged in sequence along the output light path of the laser; the mineral sample to be tested is arranged on the light output light path of the first condenser; the volume holographic grating spectrometer module comprises a filter, a second condenser and a volume holographic grating spectrometer arranged in sequence along the Raman scattered light light path of the dichroic mirror; the volume holographic grating spectrometer is used to collect and analyze the Raman scattered light of the mineral sample to be tested.

Description

Technical Field

[0001] The invention relates to an optical detection system, in particular to a Raman spectrum and lunar dust velocity measurement combined detection system. Background Art

[0002] Raman spectroscopy is a detection technology that analyzes molecular vibration and rotation modes based on the frequency shift of Raman scattered light relative to incident light and is applied to molecular structure research. Raman spectroscopy is often called the "fingerprint spectrum" of a substance. Based on the peak position, half-width, peak height, line shape and other parameters of the Raman spectrum, substances can be qualitatively identified and quantitatively analyzed.

[0003] At present, most studies are conducted on the detection of materials in the laboratory. Since the Raman spectrum signal is weak, the high diffraction efficiency of the volume holographic grating can reduce the loss of weak Raman signals in the optical path. The Raman spectrum range of minerals is relatively small, which conforms to the bandwidth characteristics of the volume holographic grating. In addition, the transmission volume holographic grating spectrometer has a simple structure and a small size, which can better meet the needs of long-distance flight. Conventional dust velocity measurements include laser Doppler velocity measurement and imaging methods. Laser Doppler velocity measurement requires the laser to be divided into two beams, which affects the subsequent collection of mineral Raman spectra.

[0004] Among the existing in-situ detection payloads on the lunar surface, there is little research on the application of Raman spectroscopy technology in the development of space-borne instruments. There is no report on the application of Raman spectroscopy in-situ detection in deep space environments, nor is there a design that integrates a mineral Raman spectrometer with a dust detection device. Summary of the invention

[0005] The purpose of the present invention is to provide a Raman spectrum and lunar dust velocity measurement combined detection system to achieve the combined detection of mineral Raman spectrum and lunar surface dust velocity in view of the fact that there are no reports on the application of Raman spectrum in situ detection in deep space environment in the existing lunar surface in-situ detection payload device, and there is no technical problem of combining mineral Raman spectrum with lunar surface dust detection device for detection.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0007] A Raman spectrum and lunar dust velocity measurement combined detection system, which is special in that it includes: a first data processing unit, a second data processing unit, a volume holographic grating spectrometer module, a laser, and a focusing mirror, a dichroic mirror, a dust particle scattered light imaging module and a first condenser arranged in sequence along the output light path of the laser;

[0008] The output light of the first condenser is irradiated onto the mineral sample to be tested, and the mineral sample to be tested emits Raman scattered light;

[0009] The Raman scattered light of the mineral sample to be tested is incident on the dichroic mirror after passing through the first condenser, and the dichroic mirror reflects the Raman scattered light to the volume holographic grating spectrometer module;

[0010] The volume holographic grating spectrometer module includes a filter, a second condenser and a volume holographic grating spectrometer which are sequentially arranged along the optical path of the Raman scattered light split by the dichroic mirror; the volume holographic grating spectrometer is used to collect and analyze the Raman scattered light of the mineral sample to be tested;

[0011] The first data processing unit is electrically connected to the volume holographic grating spectrometer module, and is used to convert the spatial distribution of the slit images of each wavelength obtained by the volume holographic grating spectrometer module into a Raman spectrum curve, and analyze the mineral components of the lunar surface dust;

[0012] The second data processing unit is electrically connected to the dust particle scattered light imaging module, and is used to perform image processing and data analysis on the dust particle motion image obtained by the dust particle scattered light imaging module to obtain the motion speed of the lunar dust in the motion state.

[0013] Furthermore, the volume holographic grating spectrometer comprises a slit, a collimating mirror, a volume holographic grating, a third condensing mirror and a first detector which are sequentially arranged along the optical path of the outgoing light of the second condensing mirror.

[0014] Further, the dust particle scattered light imaging module comprises a detection area, an objective lens and a second detector which are sequentially arranged along the light path;

[0015] The objective lens comprises a first lens, a second lens, a third lens, a fourth lens, a fifth lens and a sixth lens which are sequentially arranged along the light path of the detection area;

[0016] The first mirror is arranged near the front end of the detection area;

[0017] The second detector is arranged on the light output path of the sixth mirror.

[0018] Furthermore, the dust particle scattered light imaging module also includes a backlight panel arranged at the rear end of the detection area, and the backlight panel is used to reduce background noise interference.

[0019] Furthermore, the laser wavelength of the laser is 532nm;

[0020] The dust particle scattered light imaging module uses a visible light camera.

[0021] Furthermore, the resolution index of the volume holographic grating spectrometer is 10 cm -1 , corresponding to a spectral resolution of 0.3 nm;

[0022] The backlight panel is a backlight panel coated with a black light-absorbing coating;

[0023] The objective lens is a telecentric objective lens.

[0024] Further, the focal length of the second condenser is 70 mm;

[0025] The size of the slit is 15um;

[0026] The focal length of the collimator is 43 mm, its aperture is 19 mm, and the relative aperture D / f is 0.44;

[0027] The effective aperture of the volume holographic grating is 20 mm.

[0028] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0029] 1. The Raman spectroscopy and lunar dust velocity measurement joint detection system of the present invention integrates a volume holographic grating spectrometer module and a dust particle scattered light imaging module, that is, two types of lunar surface in-situ detection payloads, into one, and is used for the joint detection of Raman spectroscopy and lunar dust velocity measurement, which greatly reduces the weight and volume of the lunar surface in-situ detection payload and achieves the purpose of lightweighting the lunar surface in-situ detection payload.

[0030] 2. The Raman spectrum and lunar dust velocity measurement combined detection system of the present invention utilizes a laser beam emitted by the laser multiple times, greatly improving the utilization rate of laser light energy.

[0031] 3. The Raman spectrum and lunar dust velocity measurement combined detection system of the present invention replaces the traditional photomultiplier tube with a visible light camera, does not require tracer particles, and does not require a device to generate airflow. It uses direct imaging to contactlessly detect the motion trajectory of suspended dust particles on the lunar surface, and the measurement method is simple and intuitive.

[0032] 4. The Raman spectrum and lunar dust velocity measurement combined detection system of the present invention uses the imaging method to calculate the movement speed of dust using the scattered echo of laser. In activities such as planetary exploration and lunar exploration, the movement data of dust can reveal many special phenomena of planetary environment, such as glow and micromagnetosphere. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A schematic diagram of the optical path of an embodiment of a combined detection system for Raman spectroscopy and lunar dust velocity measurement according to the present invention;

[0034] Figure 2 It is a structural schematic diagram of a volume holographic grating spectrometer module in an embodiment of the Raman spectrum and lunar dust velocity measurement combined detection system of the present invention;

[0035] Figure 3 Schematic diagram of dust particle scattered light imaging module in an embodiment of the Raman spectroscopy and lunar dust velocity measurement combined detection system of the present invention.

[0036] The accompanying drawings in the figure are marked as follows:

[0037] 1-laser, 2-volume holographic grating spectrometer module, 21-filter, 22-second condenser, 23-volume holographic grating spectrometer, 231-slit, 232-collimator, 233-volume holographic grating, 234-third condenser, 235-first detector, 3-dust particle scattered light imaging module, 31-backlight plate, 32-detection area, 33-objective lens, 34-second detector, 331-first mirror, 332-second mirror, 333-third mirror, 334-fourth mirror, 335-fifth mirror, 336-sixth mirror, 4-focusing mirror, 5-dichroic mirror, 6-first condenser, 7-mineral sample to be tested. DETAILED DESCRIPTION

[0038] In order to realize the joint detection of mineral Raman spectrum and lunar dust velocity, the present invention proposes a Raman spectrum and lunar dust velocity measurement joint detection system, which fully utilizes the laser emitted by the laser 1 and does not require external airflow.

[0039] like Figure 1 As shown, the present invention provides a Raman spectrum and lunar dust velocity measurement combined detection system, which consists of a first data processing unit, a second data processing unit, a laser 1, a volume holographic grating spectrometer module 2, a dust particle scattered light imaging module 3, a focusing mirror 4, a dichroic mirror 5, a first condenser 6 and a mineral sample 7 to be tested.

[0040] like Figure 2 As shown, the volume holographic grating spectrometer module 2 unit includes a filter 21, a second condenser 22 and a volume holographic grating spectrometer 23; the volume holographic grating spectrometer 23 includes a slit 231, a collimator 232, a volume holographic grating 233, a third condenser 234 and a first detector 235;

[0041] The laser emitted by the laser 1 is focused on the surface of the mineral sample 7 to be tested by the focusing mirror 4, and the surface of the mineral sample 7 to be tested is stimulated to emit Raman scattered light. After the Raman scattered light passes through the first condenser 6 and the dichroic mirror 5, the dichroic mirror 5 splits the Raman scattered light to the volume holographic grating spectrometer module 2. After the Raman scattered light enters the volume holographic grating spectrometer module 2, the scattered light focused on the slit 231 is collimated into parallel light by the collimator 232. Then, the parallel light is split by the volume holographic grating spectrometer 23, and then the third condenser 234 converges the dispersed light of different wavelengths onto the first detector 235, and finally the spatial distribution of the slit images of each wavelength is obtained on the detector image plane. In order to further analyze the Raman spectrum characteristics of the material, the slit image is converted into a Raman spectrum curve using data quantization.

[0042] like Figure 3As shown, the dust particle scattered light imaging module 3 unit includes a backlight plate 31, a detection area 32, an objective lens 33 and a second detector 34; the objective lens 33 includes a first mirror 331, a second mirror 332, a third mirror 333, a fourth mirror 334, a fifth mirror 335 and a sixth mirror 336.

[0043] In this embodiment, the dust particle scattered light imaging module 3 uses a visible light camera to image the dust particles in the detection area 32 under a certain exposure time. After the laser 1 emits a light beam, it is converted into parallel light through a short-focal-length focusing lens 4. The particles suspended and moving on the lunar surface enter the photosensitive area, i.e., the detection area 32, and are scattered under the irradiation of the laser. The scattered light is imaged on the second detector 34 through the objective lens 33; the first data processing unit is electrically connected to the first detector 235 in the volume holographic grating spectrometer module 2, and is used to convert the spatial distribution of the slit images of each wavelength obtained by the first detector 235 into a Raman spectrum curve, and analyze the mineral components of the lunar surface dust; the second data processing unit is electrically connected to the second detector 34 in the dust particle scattered light imaging module 3, and is used to perform image processing and data analysis on the dust particle motion image obtained by the second detector 34, and obtain the motion speed of the lunar dust in the motion state. Since the particle size of lunar dust particles ranges from about 3 to 20 um, the small particle size results in a lower brightness of the image formed by the scattered light illuminated by the laser, so the second detector 34 selects a sCOMS camera suitable for weak light imaging, and the sCOMS camera must also have a higher quantum efficiency and lower readout noise. When measuring particle velocity, faster particles leave a line segment composed of points at certain intervals on the second detector 34, and the image of slower particles is a point. For faster points, by calculating the length of the line segment and the spacing between points, combined with the lens magnification and the exposure time of the sCOMS camera, the laser frequency and pulse width, the particle velocity can be effectively calculated. The experiment used a pulsed laser with a pulse frequency of 10000Hz, that is, a pulse is generated every 100us, and the pulse duration is 10ns. For a particle with a speed of 100m / s, the movement displacement within a light pulse is 1um, which is much smaller than the size of a pixel. Combined with the scattering of light, it is finally imaged as a point. When the exposure time is 200us, a particle of 100m / s passes through 2 light pulses, so the particle is imaged as two points within the exposure time. The interval between the two points is 10mm. Within the field of view, the measurement of a speed of 100 meters can be achieved. Therefore, the image method for measuring particle speed can theoretically measure the speed range of 1 to 100m / s.

[0044] For slower particles, only one point is left on an image. The frame image particle cross-correlation matching algorithm can be used to perform particle matching and center of mass positioning between two frames of images, and the particle speed can be calculated based on the time interval.

[0045] In order to reduce the interference of stray light, a backlight plate 31 coated with a black light-absorbing coating is placed on the other side opposite to the collecting light path objective lens 33 and the second detector 34 to reduce background noise interference and create a single background to facilitate the extraction of dust particles in the image for velocity analysis. The laser beam used for illumination passes through the detection area 32 and is focused on the mineral sample 7 to be tested, thereby exciting Raman scattered light to achieve full utilization of the laser.

[0046] The laser is focused on the surface of the mineral sample 7 to be tested to excite Raman scattered light, and then the Raman scattered light is split by the dichroic mirror 5 to the volume holographic grating spectrometer module 2. After the Raman scattered light enters the volume holographic grating spectrometer module 2, the scattered light focused on the slit 231 is collimated into parallel light by the collimator 232, and then split by the volume holographic grating 233, and then the dispersed light of different wavelengths is converged by the focusing mirror to the detector 234.

[0047] Since the spectral resolution of the volume holographic grating spectrometer module 2 mainly depends on the image width of the slit 231, if the half-width of the spectrum line is calculated as 5 pixels, then the pixel width of the slit 231 image on the detector image plane is 40μm. According to the imaging relationship of the spectrometer, the focal length of the collimator 232 is 43mm, and the focal length of the second condenser 22 is 70mm. It can be concluded that the maximum size of the slit 231 can be selected as 24.6um. Since Raman scattered light itself has a certain spectral broadening, in addition to the diffusion spot of the imaging system itself, we should also consider it. Therefore, we finally choose the actual size of the slit 231 to be 15um. If the 1800lpmm volume holographic grating of Wasatch Photonics is used as a reference, its effective aperture is 20mm, then according to the grating incident angle, the diameter of the collimator 232 can be calculated as D=D g cosθ=19mm. For the collimator 232, a larger object-side numerical aperture needs to be designed to collect Raman scattered light at a larger angle as much as possible. Here, NA=0.22 is selected to facilitate external optical fiber while meeting the collection capacity. Therefore, the relative aperture D / f=0.44 of the lens can be obtained, and the focal length f=43mm of the collimator 232.

[0048] According to the Kogelnik coupled wave theory, the volume holographic grating 233 can achieve a theoretical diffraction efficiency of 100% under the Bragg condition. Therefore, we select the central wavelength of 532nm in the spectrum range of the spectrometer as the Bragg incident wavelength of the volume holographic grating 233. When the diffraction order m=1, the Bragg condition of the volume holographic grating 233 can be obtained as: 2Λsinθ i =586 / n i. Under the condition of a central wavelength of 532nm, different grating line densities correspond to different Bragg angles, and the diffraction angle of the edge wavelength will also change accordingly. If the grating line density is too small, the difference in diffraction angles of different wavelengths will be small, that is, the grating dispersion rate will be reduced, which will eventually affect the reduction of spectral resolution; when using a grating with a high line density, the difference in diffraction angles of the edge wavelengths is too large, which requires the second condenser 22 to use a large field of view to collect all diffracted light. At this time, the system is prone to introduce stray light. Based on comprehensive considerations based on the currently commonly used grating constants, a grating line density of 1800lp / mm is selected, and DCG is used as the recording medium. Then the grating Bragg angle is 20.3°, and the grating incident angle in the air is 31.83°.

[0049] According to the spectral range and resolution requirements of the volume holographic spectrometer 23, two adjacent beams of 0.3nm wavelength can be separated within the wavelength range of 536-636nm, so the first detector 234 needs to meet at least a sampling interval of 0.3nm, and the spectral channels of the volume holographic spectrometer 23 should be at least (636-536) / 0.3=333.3. According to the sampling theorem, ideally a spectrum line is sampled by exactly two pixels, but in practical applications, the half-height full width of a spectrum line is about 3 to 5 pixel widths, that is, the number of sampling points is 3 to 5. If the maximum value of 5 pixel width is taken as the standard, then the detector needs at least 333*5*1665 pixels. In order to leave a certain design margin, the 2DSPC single-photon camera of Zhongzhi Keyi was finally selected, with a pixel number of 1920×1200 and a pixel size of 8μm. In this system, the horizontal 1920 pixels are set as the spectral dimension direction.

[0050] The objective lens is designed as telecentric in the object space. The specific lens parameters are: focal length 75mm, total system length 130mm, F / #=4.16, image NA=0.11, paraxial magnification 0.5. The specific parameters of each lens are shown in Table 1:

[0051] Table 1

[0052]

[0053] The working process of the above embodiment is as follows:

[0054] The laser 1 emits a 532nm pulsed laser, which is expanded into parallel light by the focusing lens 4. The dust particles suspended on the lunar surface enter the parallel light area. The particles are scattered under the irradiation of the laser, and the scattered light passes through the objective lens 33 to image it on the detector. In order to reduce the interference of stray light, a backlight plate 31 coated with a black light-absorbing coating is placed on the other side opposite to the collection light path to absorb excess scattered light. This system uses a dust particle scattered light imaging module 3, i.e., an ICCD camera to replace the original photomultiplier tube, and images the dust particles in the detection area 32 under a certain exposure time. The dust particles with faster movement speed leave a line segment composed of points at a certain interval on the second detector 34, and the image of the dust particles with slower movement speed is a point. For dust particles with faster movement speed, by calculating the length of its line segment and the spacing between points, combined with the lens magnification of the objective lens 33 and the camera exposure time, the frequency and pulse width of the laser 1, the dust particle speed can be effectively calculated. For dust particles with slower speed, only one point is left on an image. The method of matching dust particles between frames can be adopted. The dust particles are matched and the centroid is located between two frames, and the speed of the dust particles is calculated in combination with the time interval.

[0055] A focusing mirror 4 and a first condenser 6 are placed behind the parallel light area. The first condenser 6 focuses the parallel laser light on the mineral sample 7 to be tested to excite Raman scattered light, and then reflects the Raman scattered light into the volume holographic grating spectrometer module 2 through the dichroic mirror 5.

[0056] In this embodiment, two lunar surface in-situ detection payloads are integrated into one, and the Raman spectrum detection of lunar surface mineral components and the measurement of the movement speed of lunar surface dust are realized simultaneously. The wavelength of the excitation light source used to excite the mineral Raman spectrum is 532nm. The objective lens used for scattered light imaging needs to use an object-side telecentric lens. Taking into account the characteristics of the lunar surface mineral Raman spectrum, the resolution index of the designed volume holographic grating spectrometer is 10cm -1 , for a wavelength of 532nm, the corresponding spectral resolution is 0.3nm.

Claims

1. A Raman spectroscopy and lunar dust velocity measurement combined detection system, characterized in that: The device comprises a first data processing unit, a second data processing unit, a volume holographic grating spectrometer module (2), a laser (1), and a focusing mirror (4), a dichroic mirror (5), a dust particle scattered light imaging module (3) and a first condensing mirror (6) which are sequentially arranged along the output light path of the laser (1); The output light of the first condenser (6) is irradiated onto the mineral sample (7) to be tested, and the mineral sample (7) to be tested emits Raman scattered light; The Raman scattered light of the mineral sample (7) to be tested is incident on the dichroic mirror (5) after passing through the first condenser (6), and the dichroic mirror (5) reflects the Raman scattered light to the volume holographic grating spectrometer module (2); The volume holographic grating spectrometer module (2) comprises a filter (21), a second condenser (22) and a volume holographic grating spectrometer (23) which are sequentially arranged along the optical path of the Raman scattered light reflected by the dichroic mirror (5); the volume holographic grating spectrometer (23) is used to collect and analyze the Raman scattered light of the mineral sample (7) to be tested; The first data processing unit is electrically connected to the volume holographic grating spectrometer module (2) and is used to convert the spatial distribution of the slit images of each wavelength obtained by the volume holographic grating spectrometer module (2) into a Raman spectrum curve and analyze the mineral components of the lunar surface dust; The second data processing unit is electrically connected to the dust particle scattered light imaging module (3) and is used to perform image processing and data analysis on the dust particle motion image obtained by the dust particle scattered light imaging module (3) to obtain the motion speed of the lunar dust in a moving state.

2. The Raman spectroscopy and lunar dust velocity measurement combined detection system according to claim 1, characterized in that: The volume holographic grating spectrometer (23) comprises a slit (231), a collimating mirror (232), a volume holographic grating (233), a third condensing mirror (234) and a first detector (235) which are sequentially arranged along the light path of the outgoing light of the second condensing mirror (22).

3. The Raman spectroscopy and lunar dust velocity measurement combined detection system according to claim 2, characterized in that: The dust particle scattered light imaging module (3) comprises a detection area (32), an objective lens (33) and a second detector (34) which are sequentially arranged along the light output path of the focusing lens (4); The objective lens (33) comprises a first mirror (331), a second mirror (332), a third mirror (333), a fourth mirror (334), a fifth mirror (335) and a sixth mirror (336) which are sequentially arranged along the light output path of the detection area (32); The first mirror (331) is arranged near the front end of the detection area (32); The second detector (34) is arranged on the light output path of the sixth mirror (336).

4. The Raman spectroscopy and lunar dust velocity measurement combined detection system according to claim 3 is characterized in that: The dust particle scattered light imaging module (3) further comprises a backlight panel (31) arranged at the rear end of the detection area (32), and the backlight panel (31) is used to reduce background noise interference.

5. The Raman spectroscopy and lunar dust velocity measurement combined detection system according to claim 4, characterized in that: The laser wavelength of the laser (1) is 532 nm; The dust particle scattered light imaging module (3) adopts a visible light camera.

6. The Raman spectroscopy and lunar dust velocity measurement combined detection system according to claim 5, characterized in that: The resolution index of the volume holographic grating spectrometer (23) is 10 cm -1 , corresponding to a spectral resolution of 0.3 nm; The backlight panel (31) is a backlight panel coated with a black light-absorbing coating; The objective lens (33) is a telecentric objective lens.

7. The Raman spectrum and lunar dust velocity measurement combined detection system according to claim 6, characterized in that: The focal length of the second condenser (22) is 70 mm; The size of the slit (231) is 15 um; The focal length of the collimator (232) is 43 mm, the aperture is 19 mm, and the relative aperture D / f is 0.44; The effective light aperture of the volume holographic grating (233) is 20 mm.

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