Fourier near infrared spectrometer and apparatus for on-line material testing

Abstract

This invention belongs to the field of spectroscopic analysis instrument technology, and discloses a Fourier near-infrared interferometer and an instrument for online material detection. The interferometer is equipped with a pair of corner mirrors and plane mirrors, which are located on the optical paths of a moving mirror and a fixed mirror. After beam splitting, the first light ray illuminates the rotating mirror and is reflected to the hollow corner mirror. After reflection by the hollow corner mirror, it is translated back to the rotating mirror and then reflected again to the first plane mirror of the isosceles prism. After reflection by the first plane mirror, it returns along the same path. After beam splitting, the second light ray is reflected by the corner mirror, translated, and then reaches the second plane mirror. After reflection by the second plane mirror, it returns along the same path. The rotation of the rotating mirror generates a scanning optical path change. This invention uses a double-corner mirror and double-plane mirror interferometer optical path scheme, which can significantly reduce the interferometer's sensitivity to vibration and temperature, and is particularly suitable for near-infrared spectral analysis, especially online near-infrared spectral analysis.

Description

Technical Field

[0001] This invention belongs to the field of spectroscopic analysis instrument technology, and particularly relates to a Fourier transform near-infrared spectroscopy interferometer and an instrument for online material detection. Background Technology

[0002] Currently, since the 1980s, with the rapid development of computer technology, the digitalization of analytical instruments and the development of chemometrics have been driven. Chemometric methods have achieved good results in solving the problems of spectral information extraction and background interference. In addition, the unique characteristics of near-infrared spectroscopy, such as fast speed, high efficiency and low cost, have led people to re-recognize the value of near-infrared spectroscopy. It has become the fastest-growing and most eye-catching spectral analysis technology since the 1990s. It is an organic combination of spectral measurement technology and chemometrics and is known as the giant of analysis.

[0003] Unlike mid-infrared spectroscopy, which provides fingerprint signals for molecules, near-infrared spectroscopy consists of harmonics and combination frequencies of fundamental molecular signals, resulting in severe aliasing. Therefore, it was unusable before the advent of chemometrics. Modern near-infrared spectroscopy analysis techniques also heavily rely on established models and instrument stability.

[0004] Dispersive spectrometers were unsuitable for near-infrared spectroscopy due to mechanical wear and tear, a situation that was only improved with the advent of array detector near-infrared spectrometers. However, array detector near-infrared spectrometers still suffer from drawbacks such as poor detector consistency and inconsistent spectral accuracy due to instrument assembly errors. This results in the inability to transfer models, requiring independent modeling for each instrument and significantly increasing application costs.

[0005] Compared to dispersive spectrometers, time-modulated Fourier interferometric spectrometers offer advantages such as higher signal-to-noise ratio, higher wavenumber accuracy, and lower stray light. They have experienced rapid development in the last 20 years and are widely used in industrial and agricultural production, scientific research, environmental monitoring, and aerial remote sensing.

[0006] The interferometers of the first-generation Fourier spectrometers used plane mirrors for both the moving and fixed mirrors. During instrument operation, the two plane mirrors had to be kept perpendicular to each other at all times, with an angular error of less than one-thousandth of a second. This was an extremely demanding condition, making the instrument very sensitive to environmental conditions.

[0007] In the second-generation Fourier spectrometer interferometer, the moving and fixed mirrors were replaced with hollow corner mirrors. A characteristic of hollow corner mirrors is that even if their relative tilt angle to the incident light changes, they can still reflect the incident light back in perfect parallel. Therefore, rotation of the moving and fixed mirrors has no effect on the instrument's interference efficiency. However, lateral translation of the corner mirror's vertex will still reduce interference efficiency, although the degree of impact is greatly reduced.

[0008] Fourier transform spectrometers are wavelength-modulated spectrometers. The measured spectrum only matches the measured object if the measured signal remains approximately constant within a measurement cycle. Therefore, in some industrial online measurements, the measurement speed must be much greater than the speed at which the sample moves and changes.

[0009] Two requirements are necessary for near-infrared online applications of Fourier transform spectrometers: fast measurement speed and stable instrument performance.

[0010] Traditional Michelson interferometers involve the reciprocating motion of a moving mirror during operation. If the speed is too fast, vibrations are inevitable, which affect the quality of the interference light and the stability of the instrument.

[0011] Griffiths proposed a rotating mirror interferometer, which uses the rotation of a mirror to replace reciprocating motion, resulting in faster measurement speeds and less vibration. This solved the problem of measurement speed.

[0012] Griffiths proposed a rotating mirror interferometer. The radiation from the target is collimated by a front optical system and then incident on a beam splitter coated with a semi-transparent, semi-reflective film. The beam splits into a reflected beam and a transmitted beam. The reflected beam is reflected by a tilting mirror to a corner reflector, which reflects it back to the rotating mirror, then to a vertical mirror M2, and finally back to the beam splitter along the original optical path. The transmitted beam returns to the beam splitter via a vertical mirror M1 along the original optical path. The reflected beam back to the beam splitter is further split into a reflected beam and a transmitted beam, and vice versa. The transmitted portion of the reflected beam and the reflected portion of the transmitted beam are converged by a converging optical system onto a detector, generating coherent interference, which is then received by the detector. A motor drives the tilting mirror to rotate, creating a varying optical path difference between the two beams. The interference signals with different optical path differences are received by the detector, yielding a time-varying interference spectrum. After data inversion, the spectral information of the target is finally obtained.

[0013] While Griffiths proposed that the reflecting mirror interferometer eliminates the wobbling of the moving mirror and reduces the vibration of the interferometer, it still places very strict requirements on the relative positions of the plane mirrors M1 and M2 (M1 and M2 are perpendicular to each other when incident at 45 degrees; the angle between M1 and M2 is 60 degrees when incident at 30 degrees). From the incident (or exit) direction, M1 and M2 are equivalently parallel, and the angular error must be within 1 second. Instruments manufactured using this optical path are susceptible to decoupling of M1 and M2 due to temperature changes or vibrations during storage, which can decrease the interferometric modulation of the interferometer. This not only reduces the detected spectral signal but also, due to the measurement error caused by the plane mirror deflection, has a greater impact on high frequencies (short wavelengths), distorting the measured spectral curves and affecting the stability of the instrument.

[0014] In summary, the problem with existing technologies is that existing Fourier transform instruments all suffer from stability issues during online rapid measurements.

[0015] Traditional Michelson interferometers involve the reciprocating motion of a moving mirror during operation. If the speed is too fast, vibrations are inevitable, which can affect the quality of the interference light and the spectral repeatability.

[0016] Even a slight deviation in the angle between M1 and M2 of the Griffiths reflective rotating mirror interferometer will reduce the interferometric modulation of the interferometer, resulting in a smaller detected spectral signal and distortion of the measured spectral curve.

[0017] The difficulty in solving the above technical problems lies in the fact that Fourier transform spectrometers are wavelength-modulated spectrometers. Only when the measured signal remains approximately constant within a measurement cycle can the measured spectrum match that of the measured object. Therefore, in some industrial online measurements, the measurement speed must be much faster than the speed at which the sample moves. Near-infrared applications of Fourier transform spectrometers require two things: high measurement speed and stable instrument performance. These two requirements are contradictory in existing instrument designs and are difficult to balance.

[0018] The significance of solving the above technical problems: Fourier transform infrared (FTIR) spectrometers are widely recognized in the industry for their high signal-to-noise ratio and good instrument consistency, which greatly facilitates the transfer of near-infrared models between instruments. Solving these technical challenges, enabling FTIR spectrometers to achieve high-speed measurements while maintaining high stability, will allow them to move beyond the laboratory and become industrial online monitoring instruments. This will provide a solution to the urgent industrial need for transferring near-infrared models between instruments, and is expected to significantly reduce the application cost of near-infrared spectroscopy. Summary of the Invention

[0019] To address the problems existing in the prior art, the present invention provides a Fourier near-infrared spectroscopy interferometer and an instrument for online material detection.

[0020] This invention is implemented as follows: a Fourier transform near-infrared spectroscopy interferometer, comprising a beam splitter and a compensating mirror. The beam splitter first transmits and reflects the incident light (50% / 50% beam splitting). Outside the beam splitter and compensating mirror, a pair of corner mirrors and a pair of plane mirrors are respectively positioned on the reflection and transmission paths of the incident beam from the beam splitter. The corner mirrors and plane mirrors reflect the beam back to the beam splitter along its original path, where it is again transmitted and reflected (50% / 50% beam splitting) and interferes at the light exit point. A motor-driven rotating reflector is inserted into the optical path of one pair of corner mirrors and plane mirrors to refract the light. The plane of the reflector is offset from the vertical motor axis by a small angle. When the motor drives the plane mirror to rotate, a small change in the optical path of the light path is achieved, enabling optical path scanning of the interferometer. The plane mirror is carefully positioned so that the center of gravity of itself and its fixing device is located on the motor shaft, thus preventing vibration during high-speed optical path scanning when the motor rotates.

[0021] In this invention, two plane mirrors are placed near the beam splitter and are integrated with the beam splitter in an appropriate manner. The beam splitter is strictly located on the angle bisector of the angle formed by the two plane mirrors, with an error of less than 10 arcseconds (ideally less than 1 arcsecond).

[0022] Specifically, the Fourier near-infrared spectroscopy interferometer provided by the present invention is equipped with a corner mirror and a plane mirror pair, which are located on the optical paths of the moving mirror and the fixed mirror;

[0023] like Figure 1 As shown, the incident light (10) is split into two beams of approximately equal intensity after being incident on the beam splitting surface of the beam splitter (1): the first beam after splitting (11) and the second beam after splitting (16). The first beam after splitting (11) is reflected by the rotating mirror (5) into the light after the rotating mirror (12), reflected by the hollow corner mirror (7) into the light after the corner mirror (13), and then reflected by the rotating mirror (5) into the light after the rotating mirror (14) and reaching the first plane mirror (20) of the isosceles prism (4).

[0024] The first plane mirror (20) of the isosceles prism (4) vertically reflects the "ray 14 reflected by the rotating mirror" back, and after being reflected by the rotating mirror back to the "ray 13 after the corner mirror", after being reflected by the hollow corner mirror (7) back to the "ray 12 after the rotating mirror", and after being reflected by the rotating mirror back to the "first ray (11) after beam splitting", and finally returns to the beam splitting surface of the beam splitter (1) along the same path, and is split into two beams of approximately equal intensity by the beam splitting surface, one of which is the "ray 15 after the compensation mirror";

[0025] The incident light (10) is split into a second ray (16) after being reflected by the beam splitting surface. It then shines on the hollow angle mirror (8) and is reflected into a second ray (17) after being split by the hollow angle mirror. It reaches another reflecting surface (21) of the isosceles prism (4) and is reflected back to the second ray (17) after being split by the hollow angle mirror (17) by the second plane mirror (21) of the isosceles prism (4). It is then reflected back to the second ray (16) after being split by the hollow angle mirror (8) and returns to the beam splitting surface of the beam splitting mirror (1). The beam splitting surface then splits the light into two beams of approximately equal intensity, one of which is the ray (15) after the compensating mirror.

[0026] Furthermore, the incident light (10) is split into two beams by the beam splitter surface, and 50% of them become two beams of approximately equal intensity "beams behind the compensation mirror 15" after being split by the beam splitter surface. The two beams "beams behind the compensation mirror 15" are coherently superimposed.

[0027] Furthermore, the corner mirror and the plane mirror are in two pairs, located in the optical paths of the moving mirror and the fixed mirror, respectively.

[0028] Furthermore, the compensating mirror (2) is preferably made of quartz crystal, so that the reflected light and transmitted light pass through equal optical paths.

[0029] Furthermore, the rotating mirror (5) generates optical path difference scanning under the drive of the motor (6).

[0030] Furthermore, the first plane mirror (20) and the second plane mirror (21) are located near the beam splitter, or the first plane mirror (20) and the second plane mirror (21) are replaced by an isosceles prism (4).

[0031] Furthermore, the first plane mirror (20), the second plane mirror (21), the beam splitter 1, and the compensating mirror 2 constitute an optical unit.

[0032] Furthermore, the optical unit may include: an isosceles prism (4), a top cover (22), a base (23), and an intermediate support (3) and a support edge (9) bonded together by optical adhesive to form a stable frame structure; a beam splitter (1) and a compensating mirror (2) are bonded to the intermediate support (3) and fixed into the frame structure by a specific assembly device. After the assembly device is assembled, the beam splitting surface of the beam splitter (1) is located on the angle bisector of the angle between the two reflecting surfaces of the isosceles prism (4).

[0033] This invention provides an instrument for online material detection equipped with the Fourier near-infrared spectroscopy interferometer. The instrument has the following advantages: 1. It can achieve a rapid scanning speed of hundreds of times per minute without causing instrument vibration, so as to ensure that the measured signal remains approximately unchanged during each scan, thus overcoming the problem caused by material movement in online detection; 2. The isosceles prism (4), top cover (22), base (23) and support edge are bonded together with optical adhesive to form a stable optical unit, which ensures the permanent collimation of the instrument, that is, the long-term stability of the instrument, which will not be changed by temperature, humidity and vibration.

[0034] The instrument for online material detection is equipped with a narrow linewidth semiconductor laser (49) and a laser interference signal detector (48). The detector detects the signal generated after the laser emitted by the laser is interfered with by the interferometer and provides it to the control electronic board of the instrument for online material detection. The control electronic board drives the motor to rotate at a constant speed to perform optical path scanning.

[0035] Furthermore, the instrument for online liquid material detection further includes:

[0036] The near-infrared light emitted by the first halogen tungsten lamp (41) is collimated by the collimating lens (42) and enters the Fourier near-infrared spectrometer. After exiting the Fourier near-infrared spectrometer, it is converged and coupled into the first fiber head 44 by the converging lens (43). The fiber transmits the near-infrared light to the online fiber optic probe, where it is partially absorbed by the sample and carries the sample information back to the second fiber head 45. The light then exits into the converging lens 46 and converges to the first indium gallium arsenide detector 47.

[0037] The interference signal detected by the first indium gallium arsenide detector 47 is sent to the computer, and the spectrum carrying the sample absorption spectrum information is obtained by inverse Fourier transform.

[0038] Furthermore, the online fiber optic probe includes: infrared light transmitted via optical fiber exiting at the third fiber optic head 51, collimated into parallel light by the first lens 52, then reflected back by a corner mirror, interacting with the liquid sample between windows 54, being partially absorbed by the liquid sample, and carrying sample composition information, and finally converged and coupled into the fourth fiber optic head 56 by the second lens 55. The first fiber optic head 44 and the third fiber optic head 51, and the second fiber optic head 45 and the fourth fiber optic head 56 are connected by optical fibers.

[0039] The instrument spectrum used for online liquid material detection is 14000-6000 wavenumbers.

[0040] Furthermore, the instrument for online solid material detection further includes:

[0041] The light emitted by the second halogen tungsten lamp 71 is focused onto the material to be tested 73 by the fifth lens 72, and the light carried by the sample information after diffuse reflection by 74 is focused into the sixth fiber optic head 75 by the sixth lens 74.

[0042] The sixth fiber optic head 75 transmits light to the fifth fiber optic head 61. After exiting, the light is collimated into parallel light by the third lens 62 and enters the interferometer. After exiting the interferometer, the light is focused by the fourth lens 63 onto the second indium gallium arsenide detector 64.

[0043] The interference signal detected by the second indium gallium arsenide detector 64 is sent to the computer, and the spectrum carrying the sample absorption spectrum information can be obtained by inverse Fourier transform.

[0044] The instrument spectrum used for online solid material detection is 7700-3800 wavenumbers.

[0045] In summary, the advantages and positive effects of this invention are: rotating the plane mirror can achieve high-speed optical path scanning without causing vibration to the interferometer.

[0046] Once the two plane mirrors and the beam splitter are integrated into a whole in an appropriate manner, changes in the positions of other components of the interferometer will not affect the modulation of the interferometer.

[0047] This invention solves the problems of rapid scanning and stable performance of interferometers, enabling Fourier transform infrared spectrometers to be applied to industrial online detection and to detect materials in a state of flux. Attached Figure Description

[0048] Figure 1 This is a schematic diagram of the Fourier near-infrared spectroscopy interferometer provided in an embodiment of the present invention.

[0049] Figure 2 This is a schematic diagram of the optical unit structure provided in an embodiment of the present invention.

[0050] Figure 3 This is a top view of the optical unit provided in an embodiment of the present invention.

[0051] In the diagram: 1. Beam splitter; 2. Compensating mirror; 3. Central support; 4. Isosceles prism; 5. Rotating mirror; 6. Motor; 7 & 8. Hollow corner mirror; 9. Support edge; 10. Incident ray; 11. First ray after beam splitting; 12. Ray after rotating mirror; 13. Ray after corner mirror; 14. Ray reflected by rotating mirror; 15. Ray after compensating mirror; 16. Second ray after beam splitting; 17. Ray after hollow corner mirror; 18. Ray when corner mirror rotates; 20. First plane mirror; 21. Second plane mirror; 22. Top cover; 23. Base.

[0052] Figure 4 This is a structural diagram of the instrument structure for online liquid material detection using a Fourier near-infrared spectroscopy system composed of an interferometer, as described in this invention.

[0053] Figure 5Optical path structure of an online liquid detection fiber optic probe.

[0054] Figure 6 This is a structural diagram of the instrument structure for online solid material detection using a Fourier near-infrared spectroscopy system composed of an interferometer, as described in this invention.

[0055] Figure 7 Optical path structure diagram of an online probe in online solid detection.

[0056] In the diagram: 41. First halogen tungsten lamp; 42. Collimating lens; 43. First converging lens; 44. First fiber optic head; 45. Second fiber optic head; 46. Second focusing lens; 47. First indium gallium arsenide detector; 48. Laser interferometric signal detector; 49. Narrow linewidth semiconductor laser; 51. Third fiber optic head; 52. First lens; 53; 54. Window; 55. Second lens; 56. Fourth fiber optic head; 61. Fifth fiber optic head; 62. Focused onto the third lens; 64. Fourth lens; 64. Second focusing lens onto the indium gallium arsenide detector; 71. Second halogen tungsten lamp; 72. Fifth lens; 73. Material to be tested; 74. Sixth lens; 75. Sixth fiber optic head. Detailed Implementation

[0057] To further understand the invention's content, features, and effects, the following embodiments are provided, and detailed descriptions are given in conjunction with the accompanying drawings.

[0058] The Fourier near-infrared spectroscopy interferometer provided in this embodiment of the invention consists of a beam splitter, a compensating mirror, a bicorner mirror, a double plane mirror, and a rotating plane mirror.

[0059] The following is Figure 1 This interferometer is described in detail.

[0060] The incident light 10 is split into two beams of approximately equal intensity after hitting the beam-splitting surface of the beam splitter 1: a first beam 11 and a second beam 16. The transmitted first beam 11 is reflected by the rotating mirror 5 as a second beam 12, then reflected by the hollow corner mirror 7 as a third beam 13, and finally reflected by the rotating mirror 5 as a fourth beam 14. This fourth beam reaches a first plane mirror 20 of the isosceles prism 4, where it is perpendicularly reflected back by the first plane mirror 20 as a third beam 14, then reflected back by the rotating mirror 5 as a fourth beam 13, then reflected back by the hollow corner mirror 7 as a fifth beam 12, and finally reflected back by the rotating mirror 5 as a sixth beam 16. A ray 11 returns along its original path to the beam-splitting surface of beam splitter 1, where it is split into two beams of approximately equal intensity. One of these beams becomes ray 15 behind the compensating mirror. The incident light 10 is reflected by the beam-splitting surface to form a second ray 16, which then strikes the hollow angle mirror 8 and is reflected as a second ray 17 behind the hollow angle mirror. This ray reaches another reflecting surface 21 of the isosceles prism 4 and is perpendicularly reflected by the second plane mirror 21 of the isosceles prism 4, returning to ray 17 behind the hollow angle mirror. It is then reflected by the hollow angle mirror 8 and returns to ray 16, returning along its original path to the beam-splitting surface of beam splitter 1. The beam splitter then splits the light into two beams of approximately equal intensity, one of which also becomes ray 15 behind the compensating mirror. Incident light 10 is split into two beams by the beam splitter, each beam having 50% becoming "ray 15 behind the compensating mirror." These rays are then coherently superimposed on the "ray 15 behind the compensating mirror." 2 is the compensating mirror. Because the medium of the beam splitter disperses light of different wavelengths, the compensating mirror is made of the same medium as the beam splitter to ensure that the reflected and transmitted light travel equal optical paths within this medium. Rotating the reflecting mirror 5, driven by the motor 6, generates an optical path difference scan.

[0061] When the hollow corner mirror 7 deflects at a slight angle, the reflected ray changes from "ray 13 after passing through the corner mirror" to "ray 18 when the corner mirror deflects." Due to the characteristics of the corner mirror, "ray 18" remains parallel to "ray 13 after passing through the corner mirror." Therefore, when "ray 18" encounters the plane mirror 20, it is reflected back and eventually coincides with ray 12. Thus, the deflection of the corner mirror does not affect the interference modulation of the interferometer.

[0062] However, the angles of the first plane mirror 20 and the second plane mirror 21 still affect the modulation of the interferometer. The optical path folding effect of the corner mirror places the first plane mirror 20 and the second plane mirror 21 near the beam splitter. In this invention, an isosceles prism 4 replaces the first plane mirror 20 and the second plane mirror 21. Simultaneously, the first plane mirror 20, the second plane mirror 21, the beam splitter, and the compensating mirror are made into a single optical unit (see...). Figure 2 ).

[0063] There are many materials available for processing beam splitters in the near-infrared band, including calcium fluoride, barium fluoride, quartz, and even optical glass. Quartz is preferred in this invention because it has the lowest coefficient of thermal expansion, and it also allows for the use of the same material in other components of the optical unit, reducing the impact of temperature changes.

[0064] Appendix Figure 2 The optical unit proposed in this invention consists of an isosceles prism 4, a top 22, a bottom 23, a middle support 3, and a support edge 9, which are bonded together with optical adhesive to form a stable frame structure. The beam splitter 1 and the compensating mirror 2 are bonded to the middle support 3 and then fixed into the frame structure under a specific assembly device. The assembly device ensures that after assembly, the beam splitter 1 is located on the angle bisector of the angle between the two reflecting surfaces of the isosceles prism 4, with an error of less than 1 arcsecond (3600 degrees).

[0065] Appendix Figure 3 This is a top view of the optical unit proposed in this invention.

[0066] This type of optical unit is used in the interferometer optical path proposed in this invention. Figure 1 After the interferometer is activated, as long as environmental changes do not damage the structure of the optical components, temperature changes and changes in the position of the optical path components caused by external vibrations will not affect the interferometric modulation. The stability of the interferometer is greatly improved. Simultaneously, the rapidly rotating mirror allows the spectrometer to perform hundreds of spectral scans per second. Therefore, the interferometer scheme proposed in this invention solves the problems of rapid scanning and stability in interferometers, especially in online near-infrared spectral analysis.

[0067] The invention will be further described below with reference to application examples.

[0068] The interferometer of this invention was used to assemble a Fourier near-infrared spectrometer for online material detection.

[0069] Figure 4 This is a structural diagram of the instrument structure for online liquid material detection using a Fourier near-infrared spectroscopy system composed of an interferometer, as described in this invention.

[0070] The instrument is equipped with a narrow linewidth semiconductor laser 49 and a laser interference signal detector 48. The detector detects the signal generated after the laser emitted by the laser is interfered with by the interferometer, and provides it to the control electronic board of the instrument. The control electronic board drives the motor to rotate at a constant speed to achieve optical path scanning.

[0071] The near-infrared light emitted by the first halogen tungsten lamp 41 is collimated by the collimating lens 42 and then enters the interferometer of this invention. After exiting the interferometer, it is converged and coupled into the first fiber optic head 44 by the converging lens 43. The fiber optic cable transmits the near-infrared light to the online probe (…). Figure 5 The sample is partially absorbed in the online probe and carries the sample information back to the second fiber head 45, then exits into the converging lens 46 and converges to the first indium gallium arsenide detector 47.

[0072] The interference signal detected by the first indium gallium arsenide detector 47 is sent to the computer, and the spectrum carrying the sample absorption spectrum information can be obtained by inverse Fourier transform.

[0073] The instrument spectral range of this embodiment is typically 14,000-6,000 wavenumbers (0.7-1.67 micrometers).

[0074] Figure 5 This is the optical path structure of an online liquid detection fiber optic probe. Infrared light transmitted from the instrument via optical fiber is emitted at the third fiber optic head 51, collimated into parallel light by the first lens 52, then reflected back by the corner mirror, interacting with the liquid sample between the windows 54, being partially absorbed by the liquid sample, and carrying sample composition information. Finally, it is converged and coupled into the outgoing fiber optic 56 by the second lens 55.

[0075] Figure 6 This is a structural diagram of the instrument structure for online solid material detection using a Fourier near-infrared spectroscopy system composed of an interferometer, as described in this invention. Figure 7 The optical path structure of the online probe in online solid detection.

[0076] Figure 7 The light emitted by the second halogen tungsten lamp 71 is focused onto the material to be tested 73 by the fifth lens 72, and the light, which is diffusely reflected by 74, carries the sample information and is focused into the second optical fiber 75 by the lens.

[0077] The second optical fiber 75 transmits the light to... Figure 6 The fourth fiber optic head 61 emits light, which is then collimated into parallel light by the third lens 62 and enters the interferometer. After exiting the interferometer, it is focused by the fourth lens 63 onto the second indium gallium arsenide detector 64.

[0078] The interference signal detected by the second indium gallium arsenide detector 64 is sent to the computer, and the spectrum carrying the sample absorption spectrum information can be obtained by inverse Fourier transform.

[0079] The instrument spectral range of this embodiment is typically 7700-3800 wavenumbers (1.3-2.6 micrometers).

[0080] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall fall within the scope of the technical solution of the present invention.

Claims

1. A Fourier near-infrared spectroscopy interferometer, characterized in that, The Fourier near-infrared spectroscopy interferometer is equipped with a beam splitter and a compensating mirror. The beam splitter first transmits and reflects the incident light. Outside the beam splitter and the compensating mirror, a pair of corner mirrors and a pair of plane mirrors are respectively provided. The corner mirrors and the pair of plane mirrors are located on the reflection and transmission light paths of the incident beam from the beam splitter. The corner mirrors and the pair of plane mirrors reflect the beam back to the beam splitter along the original path, where it is transmitted and reflected again, and interference occurs at the light exit point. A motor-driven rotating mirror is inserted into the optical path of a pair of corner mirrors and a plane mirror to refract the light. The plane of the mirror is offset from the vertical motor axis by an angle. When the motor drives the plane mirror to rotate, the optical path of the corner mirror and the plane mirror changes, thereby realizing the optical path scanning of the interferometer. The center of gravity of both the plane mirror and the fixing device for fixing the plane mirror is located on the motor shaft; After the incident light is incident on the beam-splitting surface of the beam splitter, it is split into two beams of approximately equal intensity: a first beam and a second beam. The first beam is reflected by the rotating mirror and then reflected by the hollow corner mirror and then reflected by the rotating mirror to reach the first plane mirror of the isosceles prism. The first plane mirror of the isosceles prism reflects the light vertically, and the light is then reflected by the rotating mirror, the light after the corner mirror, the light after the rotating mirror, and the first light after the beam splitting returns to the beam splitting surface of the beam splitter. The beam splitting surface then splits the light into two beams of approximately equal intensity. One of the beams is the light after the beam splitter and the compensating mirror. The incident light, after being reflected by the beam-splitting surface, becomes a second beam after being split, which then shines on the hollow corner mirror. This second beam, after being reflected by the hollow corner mirror, reaches another reflecting surface of the isosceles prism. It is then perpendicularly reflected by the second plane mirror of the isosceles prism. The beam is then split again and returns to the beam-splitting surface of the beam-splitting mirror. The beam is then split into two beams of approximately equal intensity. One of these beams is also split into two beams of approximately equal intensity, which then pass through the beam-splitting mirror and the compensating mirror. The incident light, after being split into two beams by the beam-splitting surface of the beam splitter, is then split into two beams of approximately equal intensity by the beam-splitting surface. One of these beams becomes the light after passing through the beam splitter and the compensating mirror. The two light beams after passing through the beam splitter and the compensating mirror are coherently superimposed after the exit of the beam splitter. There are two pairs of corner mirrors and plane mirrors, located in the optical paths of the moving mirror and the fixed mirror, respectively. Both the compensating mirror and the beam splitter are quartz crystals, used to ensure that reflected and transmitted light pass through equal optical path lengths. The rotating mirror generates optical path difference scanning under the drive of the motor; Two plane mirrors are placed near the beam splitter, and the beam splitter is located on the angle bisector of the angle formed by the two plane mirrors. The first and second plane mirrors are located near the beam splitter, or an isosceles prism can be used instead of the first and second plane mirrors. The first plane mirror, the second plane mirror, the beam splitter, and the compensating mirror constitute an optical unit.

2. The Fourier near-infrared interferometer as described in claim 1, characterized in that, The optical unit may include: an isosceles prism, a top cover, a base, and a support edge bonded together by optical adhesive to form a stable frame structure; a beam splitter and a compensating lens are bonded to the intermediate support and fixed into the frame structure by an assembly device. After assembly, the beam splitter's splitting surface is located on the angle bisector of the angle between the two reflecting surfaces of the isosceles prism.

3. An instrument for online material detection equipped with the Fourier near-infrared spectroscopy interferometer according to any one of claims 1 to 2, characterized in that, The instrument for online material detection is equipped with a narrow-linewidth semiconductor laser and a laser interference signal detector. It detects the signal generated after the laser emitted by the laser is interfered with by the interferometer, and provides it to the control electronic board of the instrument for online material detection. The control electronic board drives the motor to rotate at a constant speed to perform optical path scanning.

4. The instrument for online material detection as described in claim 3, characterized in that, The instrument for online material detection further includes: The near-infrared light emitted by the first halogen tungsten lamp is collimated by a collimating lens and enters a Fourier near-infrared spectrometer. After exiting the Fourier near-infrared spectrometer, it is converged and coupled into the first fiber optic head by a converging lens. The fiber optics transmit the near-infrared light to an online fiber optic probe, where it is partially absorbed by the sample and carries the sample information back to the second fiber optic head. The light then exits into a converging lens and converges to the first indium gallium arsenide detector. The interference signal detected by the first indium gallium arsenide detector is sent to the computer, and the spectrum carrying the sample absorption spectrum information is obtained by inverse Fourier transform.

5. The instrument for online material detection as described in claim 4, characterized in that, The online fiber optic probe includes: infrared light transmitted through an optical fiber is emitted from a third fiber optic head, collimated into parallel light by a first lens, then reflected back by a corner mirror, interacting with the liquid sample between the windows, being partially absorbed by the liquid sample, and carrying sample composition information, and finally converged and coupled into the outgoing fiber by a second lens.

6. The instrument for online material detection as described in claim 3, characterized in that, The instrument for online solid material detection further includes: The light emitted by the second halogen tungsten lamp is focused onto the material to be tested by the fifth lens, and the diffusely reflected light carrying sample information is focused into the second optical fiber by the lens. The second optical fiber transmits light to the fourth optical fiber head. After exiting, the light is collimated into parallel light by the third lens and enters the interferometer. After exiting the interferometer, the light is focused by the fourth lens onto the second indium gallium arsenide detector. The interference signal detected by the second indium gallium arsenide detector is sent to the computer, and the spectrum carrying the sample absorption spectrum information can be obtained by inverse Fourier transform.

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