CN110987900A - High-sensitivity Raman spectrometer based on photomultiplier - Google Patents
High-sensitivity Raman spectrometer based on photomultiplier Download PDFInfo
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Abstract
The invention relates to a high-sensitivity Raman spectrometer based on a photomultiplier, belonging to the field of spectrometers. The high-sensitivity Raman spectrometer based on the photomultiplier is divided into a Raman light excitation and collection module and a Raman spectrum analysis module. The invention is characterized in that: in the Raman spectrum analysis module, a moving slit is combined with a photomultiplier, and high-sensitivity spectra are obtained by scanning different wavelengths point by point, so that the Raman spectrum analysis module is particularly suitable for detecting trace substances. In the Raman spectrum analysis module, a detection device can be added to quickly acquire a complete Raman spectrum as supplement. The sample to be tested can be solid, liquid or gas, and different Raman light excitation and collection modules can be selected according to different samples to be tested.
Description
Technical Field
The invention relates to a Raman spectrometer, in particular to a high-sensitivity Raman spectrometer based on a photomultiplier.
Background
Raman spectroscopy (Raman spectroscopy), is a scattering spectrum. The Raman spectroscopy is an analysis method for analyzing a scattering spectrum with a wavelength different from that of incident light to obtain information on molecular vibration and rotation based on a Raman scattering effect found by indian scientists c.v. Raman (man), and is applied to molecular structure research. With the development of laser technology, raman spectroscopy is increasingly used to detect various substances. Since different molecules have specific vibration and rotation energy levels, when laser light of a certain wavelength scatters with a certain substance molecule, a part of laser photons exchange energy with the substance molecule. After the energy exchange occurs, the laser photon wavelength changes. Because different vibration and rotation energy levels correspond to the change of the laser photon wavelength one by one, the vibration or rotation energy level difference of the molecules can be determined by analyzing the laser spectrum after scattering, and the scattered molecules are separated out according to the energy level difference to be the substance. Just as the owner of a fingerprint can be determined by a fingerprint, the species of molecules can be determined by raman spectroscopy. At the same time, the concentration of the molecule can be determined by the intensity of the raman spectrum. In recent years, with the increasing maturity of optical devices such as lasers, detectors, optical filters and the like, raman spectrometers are rapidly developed at home and abroad.
However, raman spectroscopy is mostly limited to high purity solid and liquid detection. For few raman spectrometers used for detecting trace substances and gases in solid and liquid, the photosensitive components of the raman spectrometers mostly adopt an extremely expensive ICCD (enhanced charge coupled device) or an image intensifier, and the price of the raman spectrometers is up to tens of thousands of yuan, so that the raman spectrometers are difficult to popularize. The commonly used Raman surface enhancement technology can enhance Raman signals through an enhancement chip with a surface periodic array nanostructure, and can carry out trace detection on some samples. However, the reinforcing chip has a reinforcing effect only on a part of the substance, and is often disposable, and it is difficult to form a stable industrial product.
Disclosure of Invention
The invention aims at the problems that the existing Raman spectrum detection technology is mostly limited to the detection of high-purity solid and liquid; for few Raman spectrometers for detecting trace substances and gases in solid and liquid, most of photosensitive components of the Raman spectrometer adopt an ICCD or an image intensifier which is extremely expensive; the common Raman surface enhancement technology has the problems that a surface enhancement chip cannot be repeatedly used, so that a stable industrial product is difficult to form, and the like, and provides a high-sensitivity Raman spectrometer based on a photomultiplier, which can be used for detecting solid, liquid and gas.
The technical scheme of the invention is as follows: a high-sensitivity Raman spectrometer based on a photomultiplier comprises a Raman light excitation and collection module and a Raman spectrum analysis module.
The core device of the Raman spectrum analysis module comprises: the device comprises an incident slit, a first concave reflector, a first grating, a second concave reflector, a motor, a slit, a spectrum forming lens, a photomultiplier and a computer. After the Raman light incident from the incident slit is reflected by the first concave reflecting mirror and then collimated, different wavelengths in the Raman light are diffracted to different angles on a horizontal plane by the first grating, and then are focused on different positions on a focal plane by the second concave reflecting mirror, wherein the first concave reflecting mirror, the first grating and the second concave reflecting mirror can respectively select different angles and positions as required so as to achieve the optimal spectrum forming effect. The slit is positioned on the focal plane of the second concave reflecting mirror and is fixed on the motor through a mechanical piece. The motor is a one-dimensional stepping motor or a servo motor, and different transmission wavelengths are sequentially selected by scanning the position of the motor point by point. The spectral lens is a single lens or a lens group and images the focuses with different wavelengths on the focal plane of the second concave reflector on the photosensitive surface of the photomultiplier tube. The photomultiplier tubes may be replaced with avalanche diodes or photon counters. The computer controls the motor to scan and the photomultiplier to acquire data, and the computer can be replaced by a mobile phone or a self-developed software and hardware module.
In the raman spectroscopy module, the first concave mirror and the second concave mirror may be replaced with a first lens and a second lens, respectively. After the Raman light incident from the incident slit is transmitted through the first lens for collimation, different wavelengths in the Raman light are diffracted to different angles on a horizontal plane by the first grating and then focused to different positions on a focal plane by the second lens, wherein the first lens is parallel to the incident slit surface, and the first grating and the second lens can respectively select different angles and positions as required to achieve the optimal spectrum forming effect. The slit is positioned on the focal plane of the second lens, and different transmission wavelengths are sequentially selected by scanning the position of the motor point by point.
The point-by-point scanning of different wavelengths by the cooperation of the slit, the motor, the spectrum forming lens and the photomultiplier can be one of the following embodiments: the slit is fixed on the motor and moves left and right on a second concave reflector or a second lens focal plane along with the motor, and the spectral lens and the photomultiplier are fixed; the slit and the spectrum forming lens are fixed on the motor and move left and right on a second concave reflector or a second lens focal plane along with the motor, and the photomultiplier is fixed; the slit, the spectral lens and the photomultiplier are all fixed on the motor, and the whole moves left and right on the focal plane of the second concave reflector or the second lens along with the motor; and IV, a spectral lens is not used, the slit and the photomultiplier keep a proper distance, so that the area of a light spot on a photosensitive surface of the photomultiplier is smaller than the effective receiving area, and the slit and the photomultiplier are simultaneously fixed on the motor and move left and right on a focal plane of the second concave reflector or the second lens along with the motor.
On the basis of the device, a rapid spectrum analysis device can be added: the light splitting device comprises a light splitting sheet, a second grating, a third concave reflector, a cylindrical concave lens, a cylindrical convex lens and a detector. And a light splitting sheet is inserted in the collimation position of the Raman light in front of the first grating, the light splitting sheet basically does not change the light path of the transmission part, a part of the Raman light is reflected to the second grating, the second grating diffracts different wavelengths in the Raman light to different angles on the horizontal plane, and then the Raman light is focused on different positions of the detector light sensing surface in the horizontal direction by the third concave reflector. The detector is a CCD or a CMOS. The cylindrical concave lens and the cylindrical convex lens are arranged between the third concave reflecting mirror and the detector, and the cylindrical concave lens and the cylindrical convex lens are respectively deflected by 0-10 degrees relative to the photosensitive surface of the detector. The computer is linked with the detector and controls the data acquisition of the detector.
According to different samples, one of the Raman spectrum analysis modules can be selected to be matched with different Raman light excitation and collection modules. For solid, liquid and high-concentration gas detection, the main parts of the Raman light excitation and collection module device are as follows: the device comprises a first laser, a first laser focusing lens, a first small hole, a first perforated concave reflector, a first detection point, an optical filter and a fourth concave reflector. The emergent laser of the first laser is converged by the first laser focusing lens and then passes through the first small hole in the center of the first concave reflector with holes to be focused on the first detection point. Generated at a first detection pointThe Raman light is collimated after being reflected by the first concave reflector with the hole, and is converged in the incident slit by the fourth concave reflector after the scattered laser is filtered by the optical filter. Wherein the filter is a long-wave pass or notch filter. For a solid sample, a first probe point is located on the surface of the solid; for a gas or liquid sample, the first detection point is located inside the sample. In order to achieve the best phase difference elimination effect, the focal lengths of the first concave reflector with the hole and the fourth concave reflector are respectively f1 and f2, and the deflection angles of the first concave reflector with the hole and the fourth concave reflector relative to the optical filter are respectively theta 1 and theta 2, so that the f1, the f2, the theta 1 and the theta 2 need to satisfy the relation
The distance from the center of the first holey concave mirror to the first detection point x1 is f1/cos (theta 1), and the distance from the center of the fourth concave mirror to the incident slit x2 is f2/cos (theta 2).
For detecting trace substances in gas and liquid, the Raman light excitation and collection module device mainly comprises the following parts: the second laser, the second laser focusing lens, the second small hole, the second concave reflecting mirror with holes, the fifth concave reflecting mirror, the second detection point, the seventh concave reflecting mirror, the second optical filter and the eighth concave reflecting mirror. The second laser focusing lens converges the laser and then penetrates through a second small hole in the second concave reflector with holes, the laser is reflected back and forth in a reflecting cavity formed by the second concave reflector with holes and the fifth concave reflector, two converged focuses are formed at a second detection point, the Raman light generated at the two focuses is reflected by the seventh concave reflector and then collimated, and the scattered laser is filtered by the second optical filter and then focused on the incident slit by the eighth concave reflector. In order to achieve the best phase difference elimination effect, the focal lengths of the seventh concave mirror and the eighth concave mirror are respectively f3 and f4, and the deflection angles of the seventh concave mirror and the eighth concave mirror relative to the optical filter are respectively theta 3 and theta 4, so that the relations among f3, f4, theta 3 and theta 4 need to be satisfied
The seventh concave mirror center is at f3/cos (θ 3) from the two-focus center x3, and the eighth concave mirror center is at f4/cos (θ 4) from the entrance slit x 4.
And replacing the seventh concave reflector, the second optical filter and the eighth concave reflector in the second Raman light excitation and collection module device with a third lens, a third optical filter and a fourth lens respectively, so as to obtain a third Raman light excitation and collection module device. After the Raman light generated by the two convergent focuses at the second detection point is collimated by the third lens, the scattered laser is filtered by the third optical filter, and then the Raman light is focused on the entrance slit by the fourth lens.
The invention has the beneficial effects that:
1. a high sensitivity Raman spectrometer based on a photomultiplier is provided. By switching different Raman light excitation and collection modules and Raman spectrum analysis modules, the Raman spectrum analyzer can be suitable for various solids, liquids and gases.
2. In the Raman spectrum analysis module device, a mode of matching a single-channel photomultiplier with a slit to scan wavelength is adopted, and the cost is only about ten thousand yuan. Compared with the ICCD and the image intensifier with the price of tens of thousands yuan, the cost is greatly reduced. Meanwhile, the gain multiple of the single-channel photomultiplier is higher than that of the ICCD and the image intensifier of the array, so that the sensitivity of the spectrometer is greatly improved.
3. In the rapid spectrum analysis device, two cylindrical lenses with a certain inclination angle are inserted between the third concave reflecting mirror and the detector, the size of a light spot is compressed in the vertical direction of the photosensitive surface of the detector, so that the sensitivity of the spectrometer is improved, and the specific inclination angle can further reduce the phase difference of the light spot focus in the horizontal direction, so that the resolution of the spectrometer is improved.
4. First laser focusing lens uses with the cooperation of first foraminiferous concave mirror, has saved the indispensable dichroic mirror of traditional way excitation and collection raman light method, further the cost is reduced, and this kind of device is particularly useful for the exciting light to be the raman spectroscopy appearance of ultraviolet laser light source (such as 266nm, 213 nm).
5. The Raman spectrum analysis module is matched with a reflection cavity formed by the second concave reflecting mirror with the holes and the fifth concave reflecting mirror, so that the sensitivity of detecting trace substances in gas and liquid can be greatly improved.
6. The optimal relationship among the deflection angle, the focal length, the center of the reflector and the image point distance when the first concave reflector with the hole and the fourth concave reflector and the seventh concave reflector and the eighth concave reflector are used in a matched mode is determined, and the sensitivity and the resolution ratio are further increased.
Drawings
FIG. 1 is a schematic diagram of an apparatus of a first embodiment of a Raman spectroscopy module according to the present invention;
FIG. 2 is a schematic structural diagram of an apparatus of a second embodiment of the Raman spectrum analysis module according to the present invention;
FIG. 3 is a schematic structural diagram of an apparatus of a Raman spectrum analysis module according to a third embodiment of the present invention;
FIG. 4 is a schematic structural diagram of a first embodiment of a photomultiplier-based high sensitivity Raman spectrometer of the present invention;
FIG. 5 is a schematic structural diagram of a second embodiment of a photomultiplier-based high sensitivity Raman spectrometer of the present invention;
FIG. 6 is a schematic structural diagram of a third embodiment of the photomultiplier-based high sensitivity Raman spectrometer of the present invention;
FIG. 7 is a schematic structural diagram of a fourth embodiment of the photomultiplier-based high sensitivity Raman spectrometer of the present invention;
fig. 8 is a schematic structural diagram of a fifth embodiment of the photomultiplier-based high-sensitivity raman spectrometer of the present invention.
Detailed Description
The invention is further described with reference to the following figures and examples.
A first embodiment of a raman spectroscopy module, the apparatus is shown in fig. 1: the device comprises an incident slit 1, a first concave reflector 2, a first grating 3, a second concave reflector 4, a motor 7, a slit 8, a spectrum forming lens 9, a photomultiplier 10 and a computer 11. After the raman light focused on the incident slit 1 is reflected by the first concave reflecting mirror 2 and then collimated, different wavelengths in the raman light are diffracted to different angles on a horizontal plane by the first grating 3 and then focused on different positions on a focal plane by the second concave reflecting mirror 4, wherein the first concave reflecting mirror 2, the first grating 3 and the second concave reflecting mirror 4 can be respectively arranged according to the positions of the first grating 3 and the second concave reflecting mirror 4Different angles and positions need to be selected to achieve the best spectral effect. The slit 8 is located at the focal plane of the second concave mirror 4, and the slit 8 is fixed to the motor 7 by mechanical means. The motor 7 is a one-dimensional stepping motor or a servo motor, and the position of the slit 8 on the focal plane of the second concave reflecting mirror 4 is changed by controlling the position of the motor 7, so that different transmission wavelengths are selected, and the rest wavelengths cannot be transmitted. For example, the current position can only transmit the wavelength λ corresponding to 61When the motor 7 and the slit 8 are shifted to the left, only the wavelength λ corresponding to the transmission 5 can be transmitted2. The spectral lens 9 is a single lens or a lens, and is used for imaging the focal point corresponding to each wavelength on the focal plane of the second concave reflector 4 on the photosensitive surface of the photomultiplier tube 10. The combination of the motor 7, the slit 8, the spectral lens 9 and the photomultiplier tube 10 is one of the following ways: i, a slit 8 is fixed on a motor 7 and moves left and right on a focal plane of a second concave reflector 4 along with the motor 7, and a spectral lens 9 and a photomultiplier 10 are fixed; the slit 8 and the spectrum forming lens 9 are fixed on the motor 7 and move left and right on the focal plane of the second concave reflector 4 along with the motor 7, and the photomultiplier 10 is fixed; III, the slit 8, the spectral lens 9 and the photomultiplier 10 are all fixed on the motor 7, and the whole moves left and right along with the motor 7 on the focal plane of the second concave reflector 4; and IV, a proper distance is kept between the slit 8 and the photomultiplier tube 10 without a spectral lens 9, so that the area of a light spot on the light sensing surface of the photomultiplier tube 10 is smaller than the effective receiving area, and the slit 8 and the photomultiplier tube 10 are simultaneously fixed on the motor 7 and move left and right on the focal plane of the second concave reflector 4 along with the motor 7. The photomultiplier tube 10 may also be replaced with an avalanche diode or photon counter, or other high sensitivity photon detector.
A second embodiment of the raman spectroscopy module, the apparatus is shown in fig. 2: the device comprises an incident slit 1, a first lens 12, a first grating 3, a second lens 13, a motor 7, a slit 8, a spectrum forming lens 9, a photomultiplier 10 and a computer 11. After the raman light focused on the entrance slit 1 is collimated by the first lens 12, different wavelengths in the raman light are diffracted to different angles on a horizontal plane by the first grating 3, and then focused to different positions on a focal plane by the second lens 13, wherein the first lens 12 is parallel to the entrance slit plane, and the first grating 3 and the second lens 13 can respectively select different angles and positions as required to achieve the optimal spectrum forming effect. The slit 8 is fixed to the motor 7 by mechanical means and scans the wavelength at different positions in the focal plane of the second lens 13, which is partly the same as the first embodiment of the raman spectroscopy module.
To achieve the purpose of rapidly obtaining the raman spectrum of the main material in the sample, on the basis of the first or second embodiment of the raman spectrum analysis module, a path of rapid spectrum analysis device is added as a supplement to obtain a third embodiment of the raman spectrum analysis module, as shown in fig. 3: the added components comprise a beam splitter 14, a second grating 15, a third concave reflector 16, a cylindrical concave lens 17, a cylindrical convex lens 18 and a detector 19. The beam splitter 14 is inserted in front of the first grating 3 at the raman light collimation position, the beam splitter 14 is a half-mirror, and the reflection and transmission ratio can be 10/90, 30/70, 50/50, 70/30, 90/10 and the like. The light splitting sheet 14 does not change the light path of the transmission part basically, and reflects a part of the raman light to the second grating 15, and the second grating 15 diffracts different wavelengths in the raman light to different angles on the horizontal plane, and then is focused on different positions of the light sensing surface of the detector 19 in the horizontal direction by the third concave reflecting mirror 16. A cylindrical concave lens 17 and a cylindrical convex lens 18 are interposed between the third concave mirror 16 and the detector 19 in order to compress the light in the vertical direction without substantially changing the transmission of the light in the horizontal direction. The necessity of the cylindrical concave lens 17 and the cylindrical convex lens 18 is particularly obvious for the detector 19 with a smaller photosensitive height because the photosensitive heights of different detectors 19 in the vertical direction are different. Here, the cylindrical concave lens 17 and the cylindrical convex lens 18 are each deflected by a small angle, typically 0 to 10 °, with respect to the photosensitive surface of the detector 19. This has the advantage that the horizontal phase difference of the focus corresponding to each wavelength on the photosensitive surface of the detector 19 can be further eliminated, thereby improving the resolution of the spectrometer. The cylindrical concave lens 17 and the cylindrical convex lens 18 may be replaced by one or more cylindrical lenses, each of which may be a convex lens or a concave lens, each of which is angularly offset with respect to the photosensitive surface of the detector 19. It must be ensured that the entire cylindrical lens group is equivalent to one cylindrical convex lens. The detector 19 is a CCD or CMOS. The device can rapidly acquire a complete Raman spectrum, complete rapid analysis of main substances in a sample, and is used as a supplement of the first or second implementation mode of the Raman spectrum analysis module.
The first, second and third embodiments of the raman spectroscopy module can be combined with different raman excitation and collection modules, respectively, to perform detection of different samples. For solid, liquid and high concentration gas detection, the first embodiment of the photomultiplier tube based high sensitivity raman spectrometer is shown in fig. 4. On the basis of the third embodiment of the raman spectrum analysis module, the raman light excitation and collection module device is: the device comprises a first laser 20, a first laser collimation and beam expansion lens 21, a second laser collimation and beam expansion lens 22, a first laser focusing lens 23, a first small hole 24, a first perforated concave reflector 25, a first window piece 26, a first detection point 27, an optical filter 28 and a fourth concave reflector 29. The first laser 20 may be of different laser wavelengths, e.g. 213nm,266nm, 532nm,785nm,1064nm, etc. The first laser 20 may be either a continuous laser or a pulsed laser, but generally requires a laser linewidth of less than or equal to 0.2 nm. If the laser emitted from the first laser 20 also contains other wavelength bands, a narrow-band filter needs to be placed between the first laser 20 and the first laser collimating and beam expanding lens 21 to filter out other wavelength bands. The first laser collimation beam expander lens 21 and the second laser collimation beam expander lens 22 are a telescope system, and are used for collimating and expanding the laser emitted from the first laser 20 to reduce the divergence angle, so that the first laser focusing lens 23 can focus the laser into a smaller spot at the first detection point 27. The first laser focusing lens 23 may be a single lens, a double cemented lens, or an aspheric lens. For laser light sources (e.g., 532nm,785nm,1064nm) in the visible and near infrared bands, the first laser focusing lens 23 is typically a double cemented lens or a single lens; for a laser source in the ultraviolet range (e.g., 213nm,266nm), the first laser focusing lens 23 is typically an aspheric lens or a single lens. The first holed concave mirror 25 is a concave mirror having a first small hole 24 with a diameter of about 3mm as a center so that the laser beam can pass through. The first window piece 26 is double-sidedA broadband antireflection coated N-BK7 or fused silica window plate to transmit laser and raman light. And may be solid, liquid or gas. The first detection point 27 is a laser focal point. For a solid sample, the first detection point 27 needs to be located on the sample surface; for liquid or gas samples, the first probe point 27 is located inside the liquid or gas sample to be measured in the container, since it is typically contained in a transparent container. For gas detection, the gas pressure at the first detection point 27 can be increased to 1-100 atmospheres to increase the gas concentration and thus enhance the raman optical signal light. The raman light generated at the first detection point 27 is transmitted through the first window sheet 26, reflected by the first concave mirror 25 with holes, collimated, transmitted through the optical filter 28, reflected by the fourth concave mirror 29, and focused on the entrance slit 1. The filter 28 is one or more long-wave pass or notch filters perpendicular to the collimated raman light for filtering the laser-scattered rayleigh light and transmitting the raman light. The optical path is then the same as in the third embodiment of the raman spectroscopy module. In order to achieve the best phase difference elimination effect, the focal lengths of the first concave reflector 25 with holes and the fourth concave reflector 29 with holes are f1 and f2 respectively, and the deflection angles of the first concave reflector and the fourth concave reflector relative to the optical filter are theta 1 and theta 2 respectively, so that the relationship among f1, f2, theta 1 and theta 2 needs to be satisfied
The center of the first holed concave mirror 25 is f1/cos (θ 1) from the first detection point x1, and the center of the fourth concave mirror 29 is f2/cos (θ 2) from the entrance slit x 2.
For the detection of trace substances in gas and liquid, a second embodiment of a high-sensitivity raman spectrometer based on a photomultiplier tube is adopted, as shown in fig. 5. On the basis of the first embodiment of the raman spectroscopy module, the apparatus further comprises: a second laser 30, a first plane mirror 31, a second plane mirror 32, a half-wave plate 33, a third laser collimation beam-expanding lens 34, a fourth laser collimation beam-expanding lens 35, a second laser focusing lens 36, a third plane mirror 37, a fourth plane mirror 38, a second aperture 39, a second perforated concave mirror 40, a fifth concave mirror 41, a sixth concave mirror 42, a chamber 43, a second window plate 44, a third window plate 45, a fourth window plate 46,A fifth window piece 47, a second detection point 48, a seventh concave reflector 49, a second optical filter 50, and an eighth concave reflector 51. The second laser 30 may be a different laser wavelength, e.g. 213nm,266nm, 532nm,785nm,1064nm, etc. The second laser 30 may be either a continuous or pulsed laser, but generally requires a laser linewidth of less than or equal to 0.2 nm. If the laser emitted from the second laser 30 also contains other wavelength bands, a narrow band filter is required to be placed behind the second laser 30 to filter out other wavelength bands. The first reflector 31 and the second reflector 32 are respectively fixed on the optical adjusting frame, and can perform angle fine adjustment in two directions of theta and phi so as to adjust the laser emitting direction to be parallel to the solid line square frame in fig. 5, wherein the height is the design height, and the optical adjusting frame is fixed after the adjustment is completed. Because the laser emitted by the laser is mostly linearly polarized light, and the strength of the Raman signal has a certain relation with the polarization of the excitation laser, the polarization direction of the laser line can be changed by rotating the half-wave plate 33 along the optical axis, so that the Raman signal received by the detector is strongest. The third laser collimation beam expanding lens 34 and the fourth laser collimation beam expanding lens 35 are a telescope system, and are used for collimating and expanding the laser emitted by the second laser 30 to reduce the divergence angle. The second laser focusing lens 36 is a single lens, and focuses the laser, and then reflects the laser through the third plane mirror 37 and the fourth plane mirror 38, passes through the second small hole 39 in the second concave mirror with hole 40, and focuses the laser on one focus in the second detection point 48 after transmitting through the second window sheet 44. The laser light is reflected back and forth in the reflective cavity formed by the second perforated concave mirror 40 and the fifth concave mirror 41 to form two converging focal points at the second detection point 48. The diameter and the focal length of the second concave reflector with holes 40 and the fifth concave reflector 41 are the same, the distance between the two is four times of the focal length, and the detection point 49 is positioned at the central position on the coaxial axis of the second concave reflector with holes 40 and the fifth concave reflector 41 and is two times of the focal length away from the two. The chamber 43 is provided with a second window sheet 44, a third window sheet 45, a fourth window sheet 46 and a fifth window sheet 47 on four sides respectively, the material is N-BK7 or fused quartz, and the two sides are plated with broadband antireflection films. The chamber 44 is filled with the gas or liquid to be measured, and the probe 49 is located inside the chamber 44. For gas detection, chamber 43The interior can be pressurized to 1-100 atmospheres to increase the gas concentration and thus enhance the raman optical signal. The axis of the sixth concave reflecting mirror 42 coincides with the extension lines of the two focuses in the second detecting point 48, and is away from the second detecting point 48 by twice its own focal length, so as to reflect the raman light generated at the second detecting point 48 and enhance the raman signal. The raman light generated at the second detection point 48 and the raman light reflected by the sixth concave reflecting mirror 42 are reflected by the seventh concave reflecting mirror 49 and then collimated, and then the scattered laser is filtered by the second optical filter 50 and focused on the entrance slit 1 by the eighth concave reflecting mirror 51. Wherein, the central points of the two focuses in the second detecting point 49 are located on the focus of the seventh concave reflecting mirror 49. The subsequent detection process is the same as the first embodiment of the raman spectroscopy module, and is not described in detail herein. It should be noted here that the components 30-47 in the solid line boxes in fig. 5 are perpendicular to the remaining components in fig. 5. In order to achieve the best phase difference elimination effect, the focal lengths of the seventh concave mirror 49 and the eighth concave mirror 51 are f3 and f4, respectively, and the deflection angles of the seventh concave mirror and the eighth concave mirror with respect to the filter are θ 3 and θ 4, respectively, so that the relationship among f3, f4, θ 3 and θ 4 needs to be satisfied
The center of the seventh concave mirror 49 is f3/cos (θ 3) from the center of the two focal points x3, and the center of the eighth concave mirror 51 is f4/cos (θ 4) from the entrance slit x 4.
In addition to the second embodiment of the photomultiplier tube based high-sensitivity raman spectrometer, the third embodiment of the photomultiplier tube based high-sensitivity raman spectrometer is obtained by replacing the seventh concave mirror 49, the second optical filter 50, and the eighth concave mirror 51 with the third lens 52, the third optical filter 53, and the fourth lens 54, respectively, as shown in fig. 6. The raman light generated at the second detection point 48 and the raman light reflected by the sixth concave mirror 42 are collimated by the third lens 52, then scattered laser light is filtered by the third filter 53, and then focused on the entrance slit 1 by the fourth lens 54. The rest is the same as the second embodiment of the photomultiplier-based high-sensitivity Raman spectrometer.
On the basis of the third embodiment of the photomultiplier-based high-sensitivity raman spectrometer, the second embodiment of the raman spectroscopy module is partially adopted behind the entrance slit 1, that is, the fourth embodiment of the photomultiplier-based high-sensitivity raman spectrometer is shown in fig. 7.
On the basis of the second implementation mode of the photomultiplier-based high-sensitivity raman spectrometer, a second implementation mode of a raman spectrum analysis module is partially adopted behind the entrance slit 1, namely a fifth implementation mode of the photomultiplier-based high-sensitivity raman spectrometer, as shown in fig. 8.
The computer 11 is connected with the motor 7, the photomultiplier tube 10, the detector 19, the first laser 20 and the second laser 30, and controls the scanning of the motor 7, the data acquisition of the photomultiplier tube 10 and the detector 19 and the laser output power of the first laser 20 and the second laser 30. The computer 11 may also be a mobile phone or an autonomously developed software/hardware module, which performs functions such as data acquisition, processing, storage, and interaction.
Although the present invention has been described with reference to a preferred embodiment, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (9)
1. The high-sensitivity Raman spectrometer based on the photomultiplier consists of a Raman light excitation and collection module and a Raman spectrum analysis module; the Raman spectrum analysis module comprises: the device comprises an incident slit, a first concave reflector, a first grating, a second concave reflector, a motor, a slit, a spectrum forming lens, a photomultiplier and a computer; the method is characterized in that: the Raman light incident from the incident slit is collimated after being reflected by the first concave reflector, different wavelengths in the Raman light are diffracted to different angles on a horizontal plane by the first grating, and then the Raman light is focused on different positions on a focal plane by the second concave reflector, wherein the first concave reflector, the first grating and the second concave reflector respectively select different angles and positions according to requirements to achieve the best spectral effect, the slit is positioned on the focal plane of the second concave reflector, the slit is fixed on a motor through a mechanical piece, different transmission wavelengths are sequentially selected through the position of a point-by-point scanning motor, the spectral forming lens images focuses with different wavelengths on the focal plane of the second concave reflector on a photosensitive surface of a photomultiplier, and the computer controls the motor to scan and the photomultiplier to collect data.
2. The photomultiplier-based high sensitivity raman spectrometer according to claim 1, wherein: the first concave reflector and the second concave reflector can be replaced by a first lens and a second lens respectively; after the Raman light incident from the incident slit is transmitted through the first lens for collimation, different wavelengths in the Raman light are diffracted to different angles on a horizontal plane by the first grating and then focused to different positions on a focal plane by the second lens, wherein the first lens is parallel to the incident slit surface, the first grating and the second lens can respectively select different angles and positions as required to achieve the best spectrum forming effect, the slit is positioned on the focal plane of the second lens, and different transmission wavelengths are sequentially selected through the position of a point-by-point scanning motor.
3. The photomultiplier-based high sensitivity raman spectrometer according to claim 1 or 2, wherein: the point-by-point scanning of different wavelengths by the cooperation of the slit, the motor, the spectrum forming lens and the photomultiplier adopts one of the following implementation modes: the slit is fixed on the motor and moves left and right on a second concave reflector or a second lens focal plane along with the motor, and the spectral lens and the photomultiplier are fixed; the slit and the spectrum forming lens are fixed on the motor and move left and right on a second concave reflector or a second lens focal plane along with the motor, and the photomultiplier is fixed; the slit, the spectral lens and the photomultiplier are all fixed on the motor, and the whole moves left and right on the focal plane of the second concave reflector or the second lens along with the motor; and IV, a spectral lens is not arranged, the slit and the photomultiplier tube keep a proper distance, so that the area of a light spot on a light sensing surface of the photomultiplier tube is smaller than the effective receiving area, and the slit and the photomultiplier tube are simultaneously fixed on the motor and move left and right on a focal plane of the second concave reflector or the second lens along with the motor.
4. The photomultiplier-based high sensitivity raman spectrometer according to claim 1 or 2, wherein: in order to realize the purpose of rapidly obtaining the Raman spectrum of the main substances in the sample, a rapid spectrum analysis device is added, which comprises: the light splitting sheet, the second grating, the third concave reflector, the cylindrical concave lens, the cylindrical convex lens and the detector; the light splitting sheet is inserted in the collimation position of Raman light in front of the first grating, the light path of a transmission part of the light splitting sheet is basically not changed, a part of the Raman light is reflected to the second grating, the second grating diffracts different wavelengths in the Raman light to different angles on a horizontal plane, then the Raman light is focused on different positions of a light sensing surface of the detector in the horizontal direction by the third concave mirror, the detector is a CCD or a CMOS, the cylindrical concave lens and the cylindrical convex lens are arranged between the third concave mirror and the detector, and the cylindrical concave lens and the cylindrical convex lens respectively deflect 0-10 degrees relative to the light sensing surface of the detector.
5. The photomultiplier-based high sensitivity raman spectrometer according to claim 1 or 2, wherein: for solid, liquid and high concentration gas detection, the Raman light excitation and collection module device comprises: the device comprises a first laser, a first laser focusing lens, a first small hole, a first perforated concave reflector, a first detection point, an optical filter and a fourth concave reflector; the method comprises the following steps that emergent laser of a first laser is converged by a first laser focusing lens, then penetrates through a first small hole in the center of a first perforated concave reflector, and is focused on a first detection point, Raman light generated at the first detection point is reflected by the first perforated concave reflector and then is collimated, scattered laser is filtered by an optical filter, then the scattered laser is converged in an incident slit by a fourth concave reflector, wherein the optical filter is a long-wave pass or notch optical filter, and the optical filter is perpendicular to the collimated Raman light; for a solid sample, a first probe point is located on the surface of the solid; for a gas or liquid sample, the first detection point is located inside the sample(ii) a For a gas sample, when the Raman optical signal is weaker, the effect of enhancing the Raman optical signal is realized by increasing the gas pressure; the focal lengths of the first concave reflector with holes and the fourth concave reflector with holes are f1 and f2 respectively, and the deflection angles of the first concave reflector with holes and the fourth concave reflector with respect to the optical filter are theta 1 and theta 2 respectively, so that the relationship among f1, f2, theta 1 and theta 2 needs to be satisfied
The distance from the center of the first holey concave mirror to the first detection point x1 is f1/cos (theta 1), and the distance from the center of the fourth concave mirror to the incident slit x2 is f2/cos (theta 2).
6. The photomultiplier-based high sensitivity raman spectrometer according to claim 1 or 2, wherein: for detecting trace substances in gas and liquid, the Raman light excitation and collection module device comprises: the second laser, the second laser focusing lens, the second small hole, the second concave reflecting mirror with holes, the fifth concave reflecting mirror, the second detection point, the seventh concave reflecting mirror, the second optical filter and the eighth concave reflecting mirror; the second laser focusing lens converges the laser and then penetrates through a second small hole in the second perforated concave reflector, the laser is reflected back and forth in a reflecting cavity formed by the second perforated concave reflector and the fifth concave reflector, two converged focuses are formed at a second detection point, the Raman light generated at the two focuses is reflected by the seventh concave reflector and then collimated, the scattered laser is filtered by the second optical filter and then focused on an incident slit by the eighth concave reflector, and the second optical filter is perpendicular to the collimated Raman light; for a gas sample, when the Raman optical signal is weaker, the effect of enhancing the Raman optical signal is realized by increasing the gas pressure; the focal lengths of the seventh concave reflector and the eighth concave reflector are respectively f3 and f4, and the deflection angles of the seventh concave reflector and the eighth concave reflector relative to the optical filter are respectively theta 3 and theta 4, so that the relationship among f3, f4, theta 3 and theta 4 needs to be satisfied
The seventh concave mirror center is at f3/cos (θ 3) from the two-focus center x3, and the eighth concave mirror center is at f4/cos (θ 4) from the entrance slit x 4.
7. The photomultiplier-based high sensitivity raman spectrometer according to claim 6, wherein: in order to adjust the light path conveniently, the seventh concave reflecting mirror, the second optical filter and the eighth concave reflecting mirror are replaced by a third lens, a third optical filter and a fourth lens respectively; after the Raman light generated by the two convergent focuses at the second detection point is collimated by the third lens, the scattered laser is filtered by the third optical filter, and then the Raman light is focused on the entrance slit by the fourth lens.
8. The photomultiplier-based high sensitivity raman spectrometer according to claim 1 or 2, wherein: the photomultiplier tubes are replaced with avalanche diodes or photon counters.
9. The photomultiplier-based high sensitivity raman spectrometer according to claim 1 or 2, wherein: the computer is replaced by a mobile phone or a self-developed software and hardware module.
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