A laser absorption spectroscopy measurement system and method based on adaptive spectral compensation

Abstract

The present application relates to laser absorption spectroscopy, in particular to a kind of laser absorption spectroscopy measurement system and method based on adaptive spectral compensation, basic structure includes light source module, transmission module, spectral compensation module, photoelectric detection module and control module.Light source module emits wavelength adjustable laser;Transmission module transmits laser to sample stage, then the laser emitted from sample stage is transmitted to spectral compensation module;Spectral compensation module transmits laser to photoelectric detection module and adjusts the light intensity entering photoelectric detection module;Photoelectric detection module converts the received laser into data electrical signal and transmits to control module;Control module receives the electrical signal of light source module and photoelectric detection module and controls spectral compensation module.The present application introduces closed loop negative feedback control and lower cost spectral compensation module, the amplitude of background spectrum measured by adaptive spectral compensation realized by the present application is closer to the measurement upper limit of photoelectric detection module, thereby reducing the dynamic range noise, detector noise and shot noise of system, and the signal-to-noise ratio of system is improved.

Description

Technical Field

[0001] This invention relates to the field of laser absorption spectroscopy, and in particular to a laser absorption spectroscopy measurement system and method based on adaptive spectral compensation. Background Technology

[0002] Absorption spectroscopy refers to the spectrum produced when a substance absorbs photons and transitions from a lower energy level to a higher energy level. Absorption spectra contain the structure and motion states of atoms, molecules, and other substances in the sample. Laser absorption spectroscopy refers to the absorption spectrum measured using a laser as a light source. The spectral radiance of lasers is higher than that of other types of light sources, which is advantageous for obtaining absorption spectra with higher signal-to-noise ratios.

[0003] To increase the detectable material types in laser absorption spectroscopy measurement systems, a wider operating wavelength light source is needed, such as broadband and wavelength-tunable sources. Fluctuations in the spectral radiance of the laser source within its operating wavelength, along with strong absorption peaks of uninterested background components in the sample within the measurement wavelength, collectively lead to significant amplitude fluctuations in the spectrum entering the photodetector module. Meanwhile, the measurement range of the photodetector module is limited. To avoid saturation, existing spectral measurement systems often use devices with similar attenuation capabilities for various laser wavelengths, including slits, gold meshes, and neutral density filters. However, this results in a reduction in the intensity of some wavelengths that were originally within the measurement range, thereby increasing dynamic range noise, detector noise, and shot noise in these wavelength ranges.

[0004] In 2021, Chon, Bonghwan et al. published a paper titled "Compensation of Strong Water Absorption in Infrared Spectroscopy Reveals the Secondary Structure of Proteins in Dilute Solutions" in Volume 93, Issue 4 of *Analytical Chemistry*. This paper described the relationship between the dynamic range noise, detector noise, shot noise, and the light intensity measured by the system's photodetector module in a laser absorption spectroscopy measurement system. They implemented adaptive spectral compensation applicable to various sample conditions using two cascaded acousto-optic modulators (AOMs), improving the system's signal-to-noise ratio. However, AOMs have limited operating bands, requiring different AOMs for different spectral ranges, increasing the cost of spectral compensation. Furthermore, taking AOMs manufactured by Brimrose Corporation as an example, their diffraction efficiency is limited; only about 80% of the light intensity entering the AOM can reach the subsequent optical path, and in some bands, even less than 50%. Summary of the Invention

[0005] This invention provides a laser absorption spectroscopy measurement system and method based on adaptive spectral compensation, which is applicable to the laser absorption spectroscopy measurement of various samples (including gas, liquid, and solid samples). The spectral compensation module used is low-cost and easy to operate, and the laser loss can be adjusted within 0-100%, without limiting the spectral measurement range of the system. During the period when the laser emitted from the light source module is scanning the wavelength, the light intensity entering the photodetector module can be adaptively adjusted according to the measurement requirements, so that the overall amplitude of the measured background spectrum is closer to the upper limit of the photodetector module, thereby reducing the dynamic range noise, detector noise, and shot noise of the system.

[0006] The objective of this invention is achieved through the following technical means.

[0007] According to one aspect of the present invention, a laser absorption spectroscopy measurement system based on adaptive spectral compensation is provided, characterized in that the system comprises five parts: a light source module, a transmission module, a spectral compensation module, a photoelectric detection module, and a control module;

[0008] The light source module is used to output wavelength-tunable laser light and an electrical signal synchronized with the laser output.

[0009] The transmission module is used to transmit the laser to the sample stage, and then transmit the laser emitted from the sample stage to the spectral compensation module;

[0010] The spectral compensation module includes an adjustable slit and an electric displacement stage. The adjustable slit is mounted on the electric displacement stage and its width is fixed to the same size as the diameter of the laser beam entering the spectral compensation module. The electric displacement stage receives a control signal from the control module and adjusts its displacement according to the control signal, thereby adjusting the blocking ratio of the adjustable slit on the laser beam and adjusting the laser light intensity entering the photoelectric detection module.

[0011] The photoelectric detection module is used to convert the received laser light intensity value into a data electrical signal and transmit it to the control module;

[0012] The control module is connected to the light source module and the photoelectric detection module. It is used to calculate the required control signal based on the data electrical signal and transmit it to the spectral compensation module, thereby realizing the closed-loop negative feedback control function. This makes the background spectrum closer to the measurement upper limit of the photoelectric detection module, thereby reducing the dynamic range noise, detector noise and shot noise of the system and improving the signal-to-noise ratio of the system. At the same time, the control module is also used to process the data electrical signal and calculate the laser absorption spectrum.

[0013] Optionally, the light source module includes a power supply, a laser driver, a temperature controller, and a laser tube; the power supply provides energy to the laser driver and the temperature controller; the laser driver controls laser emission; the laser driver and the temperature controller together control the scanning speed and scanning range of the center wavelength of the laser and maintain stable laser output; the laser tube outputs the laser.

[0014] Optionally, the transmission module includes an off-axis parabolic mirror one, a sample stage, and an off-axis parabolic mirror two; the off-axis parabolic mirror one is used to focus the laser onto the sample stage; the sample stage is used to fix the sample to be tested; the off-axis parabolic mirror two is used to collimate the laser emitted from the sample stage and allow the laser to enter the spectral compensation module.

[0015] Optionally, the spectral compensation module can also be replaced by a galvanometer or other similar rapidly flip-up devices. The galvanometer is used to adjust the transmission direction of the laser entering the spectral compensation module, thereby adjusting the spatial obstruction ratio of the laser before it enters the photoelectric detection module. The response speed of the galvanometer is usually faster than that of the electric displacement stage, which can improve the spectral scanning speed and spectral resolution of the system.

[0016] Optionally, the photoelectric detection module includes an off-axis parabolic reflector and a photoelectric conversion device; the off-axis parabolic reflector is used to converge the laser emitted from the spectral compensation module into the photoelectric conversion device.

[0017] Optionally, the control module includes a lock-in amplifier, a data acquisition card, and a control computer; the lock-in amplifier is used to demodulate the data electrical signal output by the photoelectric detection module; the data acquisition card is used to read the demodulation result of the lock-in amplifier and the electrical signal synchronized with the laser output by the light source module in real time, and transmit them to the control computer; the control computer is used to store the demodulation result and integrate it into spectral data, process the background spectral data collected when the sample stage is empty or when a reference sample is placed, and the sample spectral data collected when the sample to be tested is placed on the sample stage, and obtain the laser absorption spectrum; the control computer is also used to control the data acquisition card to output control electrical signals for controlling the spectral compensation module.

[0018] Optionally, the control module has two switchable operating modes. In the first operating mode, the control computer, according to pre-written settings, causes the data acquisition card to output the control electrical signal to complete the acquisition of background spectral data or sample spectral data. In the second operating mode, the control computer calculates the control electrical signal transmitted from the data acquisition card to the spectral compensation module in real time based on the deviation between the demodulation result transmitted from the data acquisition card and the expected value. The spectral compensation module adjusts the laser light intensity entering the photoelectric detection module according to the control electrical signal, thereby adjusting the demodulation result read by the data acquisition card in real time in the next moment, realizing a closed-loop negative feedback control function.

[0019] According to another aspect of the present invention, a laser absorption spectroscopy measurement method based on adaptive spectral compensation is provided, which is executed using the aforementioned laser absorption spectroscopy measurement system based on adaptive spectral compensation. The laser absorption spectroscopy measurement method based on adaptive spectral compensation includes the following steps:

[0020] (1) Background spectrum measurement preparation: Set the expected value and acceptable deviation of the background spectrum amplitude in the control module, clean the sample stage and place the reference sample or empty sample stage as needed, and set the spectral compensation module to the initial state.

[0021] (2) Turn on the light source module, the light source module outputs laser and the center wavelength of the laser scans according to the set scanning speed and scanning range;

[0022] (3) Measure the light intensity value. The laser output by the light source module enters the photoelectric detection module through the transmission module and the spectral compensation module. The photoelectric detection module converts the received laser light intensity value into a data electrical signal and transmits it to the control module.

[0023] (4) Adaptive spectral compensation: The control module calculates the control signal to be transmitted to the spectral compensation module in real time based on the deviation between the data electrical signal transmitted from the photoelectric detection module and the expected value. The spectral compensation module adjusts the laser light intensity entering the photoelectric detection module according to the control electrical signal, thereby adjusting the data electrical signal received by the control module in the next moment, realizing the closed-loop negative feedback control function. The control module stores the calculated control electrical signals and integrates them into a sequence.

[0024] (5) Optimize the spectral compensation effect. The control module adjusts the corresponding stored control electrical signal sequence according to the deviation between the measured background spectrum and the expected value, and controls the spectral compensation module according to the adjusted control electrical signal sequence to complete the acquisition of new background spectral data. Repeat this step until the deviation between the background spectrum and the expected value is less than the acceptable deviation.

[0025] (6) Measure the spectrum of the sample, fix the sample to be tested on the sample stage, and let the control module control the spectral compensation module according to the control electrical signal sequence finally obtained in step 5.

[0026] (7) Calculate the laser absorption spectrum of the sample to be tested. The background spectrum and the sample spectrum are processed by the control module to obtain the laser absorption spectrum of the sample to be tested. The background spectrum is closer to the measurement limit of the photoelectric detection module than before the spectral compensation, thereby reducing the dynamic range noise, detector noise and shot noise of the system and improving the signal-to-noise ratio of the laser absorption spectrum of the sample to be tested.

[0027] The gain effect of the present invention:

[0028] (1) The present invention discloses an adaptive spectral compensation laser absorption spectral measurement system. The spectral compensation module can be freely set to the attenuation ratio of each wavelength in the background spectrum without imposing any limitations on the spectral measurement range of the system. At the same time, the spectral compensation module can use electrical signals as control signals, making it easy to operate.

[0029] (2) The laser absorption spectral measurement system with adaptive spectral compensation disclosed in this invention uses a slit and an electric displacement stage, or a galvanometer to replace the plane mirror in the system, while ensuring the spectral measurement range and spectral compensation effect of the system. This avoids the use of expensive devices such as broadband acousto-optic modulators.

[0030] (3) The present invention discloses an adaptive spectral compensation laser absorption spectral measurement system and method. The spectral compensation module, photoelectric detection module and control module realize closed-loop negative feedback control, which can automatically adjust the spectral compensation effect according to the measurement requirements, so that the amplitude of the background spectrum is closer to the measurement upper limit of the photoelectric detection module, thereby reducing the dynamic range noise, detector noise and shot noise of the system and improving the signal-to-noise ratio of the system.

[0031] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of the present invention, nor is it intended to limit the scope of the invention. Other features of the invention will become readily apparent from the following description. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a schematic diagram of a laser absorption spectroscopy measurement system based on adaptive spectral compensation.

[0034] Figure 2 The background spectra measured before and after spectral compensation when no sample is loaded, as provided in the embodiments of the present invention;

[0035] Figure 3 This is a flowchart illustrating a laser absorption spectroscopy measurement method based on adaptive spectral compensation, provided as an embodiment of the present invention.

[0036] The reference numerals in the attached diagram are listed below: 1-Light source module, 2-Transmission module, 3-Spectral compensation module, 4-Photoelectric detection module, 5-Control module. Detailed Implementation

[0037] To enable those skilled in the art to better understand the objectives, technical solutions, and advantages of this invention, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are merely some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort should fall within the scope of protection of this invention.

[0038] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0039] Figure 1 This is a structural diagram of a first laser absorption spectroscopy measurement system based on adaptive spectral compensation, provided as an embodiment of the present invention. (Reference) Figure 1 The laser absorption spectroscopy measurement system based on adaptive spectral compensation consists of five parts: a light source module 1, a transmission module 2, a spectral compensation module 3, a photoelectric detection module 4, and a control module 5. The light source module 1 outputs a wavelength-tunable laser and an electrical signal synchronized with the laser output. The transmission module 2 includes a sample stage for transmitting the laser to the sample stage, and then transmitting the laser emitted from the sample stage to the spectral compensation module 3. The spectral compensation module 3 includes an adjustable slit and a motorized displacement stage. The adjustable slit is mounted on the motorized displacement stage, and its width is fixed to the same size as the diameter of the laser beam entering the spectral compensation module 3. The motorized displacement stage receives a control signal from the control module 5 and adjusts its displacement according to the control signal, thereby adjusting the blocking ratio of the adjustable slit on the laser beam and adjusting the laser intensity entering the photoelectric detection module 4. The detection module 4 converts the received laser intensity value into a data electrical signal and transmits it to the control module 5. The control module 5 is connected to the light source module 1 and the photoelectric detection module 4. It calculates the required control electrical signal based on the data electrical signal transmitted from the photoelectric detection module 4 and transmits it to the spectral compensation module 3, thereby realizing the closed-loop negative feedback control function. This makes the background spectrum closer to the measurement upper limit of the photoelectric detection module 4, thereby reducing the dynamic range noise, detector noise, and shot noise of the system and improving the signal-to-noise ratio of the system. At the same time, the control module 5 is also used to process the data electrical signal and calculate the laser absorption spectrum.

[0040] In this embodiment, the key performance indicator for the light source module 1 is the spectral scanning speed. Since the spectral compensation module has a certain response time (depending on the response time and displacement speed of the electric displacement stage), a slower spectral scanning speed results in better spectral compensation. Other key performance indicators, such as operating wavelength range, average power, and pulse repetition frequency, depend on the actual application requirements, including the sample under test, effective optical path, and environmental noise suppression. The sample stage can be a gas cell, liquid cell, or attenuated total reflection crystal, depending on the measurement requirements. The key performance indicators for the spectral compensation module 3 are the response time and the repeatability of the electric displacement stage. The product of the response time of the spectral compensation module 3 and the spectral scanning speed of the light source module 1 should be as small as possible compared to the sample's spectral resolution requirements. The repeatability of the electric displacement stage refers to the deviation in displacement when the electric displacement stage receives the same control signal multiple times. In this embodiment, this deviation is less than 8 μm. With the same beam diameter (in this embodiment, the beam diameter illuminating the slit is less than 4 mm), a larger deviation results in poorer repeatability of the background spectral measurement.

[0041] The technical solution of this embodiment outputs a wavelength-tunable laser and an electrical signal synchronized with the laser output through a light source module. A transmission module transmits the laser to a sample stage, and the laser emitted from the sample stage is transmitted to a spectral compensation module. The spectral compensation module adjusts its displacement based on the control electrical signal from the control module, thereby adjusting the laser intensity entering the photodetector module. The photodetector module converts the received laser intensity value into a data electrical signal and transmits it to the control module. The control module calculates and stores the required control electrical signal based on the data electrical signal from the photodetector module and transmits it to the spectral compensation module, thus achieving a closed-loop negative feedback control function. This makes the background spectrum closer to the measurement upper limit of the photodetector module, thereby reducing the dynamic range noise, detector noise, and shot noise of the system, and improving the signal-to-noise ratio of the system. After the background spectrum is acquired, the control module causes the spectral compensation module to shift according to the control electrical signal stored during the background spectrum measurement, and then acquires the sample spectrum. The control module processes the data electrical signals of the background spectrum and the sample spectrum and finally calculates the laser absorption spectrum.

[0042] Based on the above technical solution, optionally, the light source module includes a power supply, a laser driver, a temperature controller, and a laser tube. The power supply provides energy to the laser driver and temperature controller. The laser driver controls laser emission. The laser driver and temperature controller jointly control the scanning speed and scanning range of the laser's center wavelength and maintain stable laser output. The laser tube outputs the laser. In specific implementations, the power supply, laser driver, temperature controller, and laser tube can be set separately or integrated together; this embodiment of the invention does not limit this.

[0043] Optionally, the transmission module includes an off-axis parabolic mirror one, a sample stage, and an off-axis parabolic mirror two. The off-axis parabolic mirror one is used to focus the laser onto the sample stage, the sample stage is used to fix the sample to be tested, and the off-axis parabolic mirror two is used to collimate the laser emitted from the sample stage and allow the laser to enter the spectral compensation module.

[0044] Optionally, the spectral compensation module can also replace the combination of the slit and the motorized displacement stage with a galvanometer or other similar rapidly flip-up galvanometer. The galvanometer or other similar rapidly flip-up galvanometer is used to adjust the transmission direction or degree of obstruction of the laser entering the spectral compensation module, thereby adjusting the intensity of the laser entering the photodetector module. The response speed of the galvanometer is generally faster than that of the motorized displacement stage, which can improve the spectral scanning speed and spectral resolution of the system. However, the operating wavelength of the galvanometer depends on the material and manufacturing process of the mirror, which limits the spectral measurement range of the system. In this embodiment, the operating wavelength of the galvanometer is 0.45-10.6 μm. This parameter is for reference only; other operating wavelengths can be selected according to measurement requirements. This embodiment of the invention does not limit this.

[0045] Optionally, the photoelectric detection module includes an off-axis parabolic mirror and a photoelectric conversion device. The off-axis parabolic mirror is used to focus the laser emitted from the spectral compensation module as completely as possible into the photoelectric conversion device. The off-axis parabolic mirror and other off-axis parabolic mirrors in this invention can also be replaced with lenses or other types of focusing lenses. In this embodiment, a silver-coated or gold-coated off-axis parabolic mirror is used to reduce attenuation of laser light in the mid-infrared band. The photoelectric conversion device can include single-pixel and multi-pixel devices for converting the received laser intensity value into a data electrical signal and transmitting it to the control module. In specific implementations, the off-axis parabolic mirror and the photoelectric conversion device can be set separately or integrated together; this embodiment of the invention does not limit this.

[0046] Optionally, the control module includes a lock-in amplifier, a data acquisition card, and a control computer. The lock-in amplifier demodulates the data signal output by the photodetector module, suppressing noise in the signal whose frequency differs from the laser pulse repetition frequency. The data acquisition card reads the demodulation results from the lock-in amplifier and the laser-synchronized electrical signal output by the light source module in real time and transmits them to the control computer. The control computer stores the demodulation results and integrates them into spectral data. It processes the background spectral data collected when the sample stage is empty or when a reference sample is placed, as well as the sample spectral data collected when the test sample is placed on the sample stage, to obtain the laser absorption spectrum. The control computer also controls the data acquisition card to output control signals for controlling the spectral compensation module.

[0047] Optionally, the control module has two switchable operating modes. In the first mode, the control computer, according to pre-written settings, causes the data acquisition card to output control electrical signals to complete the acquisition of background spectral data or sample spectral data. In the second mode, the control computer calculates the control electrical signal that needs to be transmitted from the data acquisition card to the spectral compensation module in the next moment based on the deviation between the demodulation result transmitted from the data acquisition card and the expected value. The spectral compensation module adjusts the laser light intensity entering the photoelectric detection module according to the control electrical signal, thereby adjusting the demodulation result read by the data acquisition card in real time in the next moment, realizing the closed-loop negative feedback control function.

[0048] In one specific embodiment of the present invention, the light source module 1 emits a collimated laser beam and an electrical signal synchronized with the laser, wherein the wavelength scanning range of the laser is approximately 6-10 μm (wavenumber range of 1670-972 cm⁻¹). -1 The scanning speed is 0.5 cm. -1 / s, line width 2cm -1 The pulse width is 60ns, the repetition frequency is 1MHz, and the minimum average power within the tunable wavelength range is 1mW. Figure 2 The illustration shows the background spectrum measured before spectral compensation in this specific embodiment. This background spectrum reflects the output spectral characteristics of the light source module used in this specific embodiment. The system of this specific embodiment utilizes the wavelength tunable characteristics of the laser to perform spectral compensation during wavelength scanning, and can acquire the spectrum without using additional spectroscopic elements. The transmission module 2 uses an off-axis parabolic reflector with a silver coating to focus the laser onto the sample stage, and uses another off-axis parabolic reflector with a silver coating to collimate the laser emitted from the sample stage and transmit it to the spectral compensation module 3. The spectral compensation module 3 includes an adjustable slit and an electric displacement stage. The adjustable slit is mounted on the electric displacement stage and its width is fixed at 4 mm, the same as the diameter of the laser beam entering the spectral compensation module 3. The electric displacement stage receives a control signal from the control module 5 and adjusts its displacement according to the control signal, thereby adjusting the blocking ratio of the adjustable slit on the laser beam and adjusting the laser intensity entering the photodetector module 4. Photoelectric detection module 4 includes an off-axis parabolic reflector with a silver-plated mold and a mid-infrared photodetector unit. The off-axis parabolic reflector with the silver-plated mold is used to focus the laser onto the photoelectric conversion device. The normalized detectivity of the mid-infrared photodetector unit is greater than 2 × 10⁻⁶ μm in the range of 3–11 μm. 8 cm·Hz 1 / 2The system includes a 100MHz bandwidth operational amplifier to convert the received infrared laser light into a data signal and transmit it to the control module 5. The control module 5, connected to the light source module 1 and the photoelectric detection module 4, includes a lock-in amplifier, a data acquisition card, and a control computer. The lock-in amplifier demodulates the amplitude of the 1MHz electrical signal, suppressing noise at other frequencies. The data acquisition card reads the demodulation results from the lock-in amplifier and the laser-synchronized electrical signal output from the light source module 1 in real time and transmits it to the control computer. The data acquisition card also outputs control signals to the spectral compensation module according to instructions from the control computer. The control computer stores the demodulation results and integrates them into spectral data. It processes background spectral data collected when the sample stage is empty or with a reference sample, as well as sample spectral data collected when the sample to be tested is placed on the sample stage, to obtain the laser absorption spectrum. The control computer also controls the data acquisition card to output control signals for controlling the spectral compensation module. The control module has two switchable operating modes. In the first mode, the control computer, according to pre-programmed settings, causes the data acquisition card to output control electrical signals to complete the acquisition of background spectral data or sample spectral data. In the second mode, the control computer calculates the control electrical signal that needs to be transmitted from the data acquisition card to the spectral compensation module in the next moment based on the deviation between the demodulation result transmitted from the data acquisition card and the expected value. The spectral compensation module adjusts the laser intensity entering the photoelectric detection module according to the control electrical signal, thereby adjusting the demodulation result read by the data acquisition card in real time in the next moment, realizing the closed-loop negative feedback control function.

[0049] Figure 3 This is a flowchart illustrating a laser absorption spectroscopy measurement method based on adaptive spectral compensation provided in an embodiment of the present invention. The laser absorption spectroscopy measurement method based on adaptive spectral compensation provided in this embodiment is executed using the laser absorption spectroscopy measurement system based on adaptive spectral compensation provided in the above specific embodiment. Figure 2 The background spectrum after spectral compensation obtained in this embodiment is shown. Compared with the background spectrum before spectral compensation, the overall spectrum is closer to the measurement upper limit of the photoelectric detection module. (Reference) Figure 3 The laser absorption spectroscopy measurement method based on adaptive spectral compensation includes the following steps:

[0050] Step 1, Background Spectrum Measurement Preparation: Set the expected value and acceptable deviation of the background spectral amplitude in the control computer; clean the sample stage and place the reference sample or empty sample stage as needed; set the spectral compensation module to the initial state.

[0051] In this embodiment of the invention, the expected value is set to a normalized light intensity value of 0.9, the acceptable deviation is -2 to 0.99, and the loss is set to 0% in the band where the light intensity is too weak to reach the acceptable deviation.

[0052] Step 2, turn on the light source module: The light source module outputs laser light and makes the center wavelength of the laser light scan according to the set scanning speed and scanning range.

[0053] In this embodiment of the invention, the wavenumber scanning range is set to 1670-972 cm⁻¹. -1 The scanning speed is 0.5cm. -1 / s.

[0054] Step 3, measuring light intensity: The laser output from the light source module enters the photoelectric detection module through the transmission module and the spectral compensation module. The photoelectric detection module converts the received laser light intensity value into a data electrical signal and transmits it to the lock-in amplifier in the control module. The data acquisition card in the control module reads the demodulation result of the lock-in amplifier and transmits it to the control computer.

[0055] Step 4, Adaptive Spectral Compensation: The control module operates in the second working mode. The control computer calculates the control electrical signal transmitted from the data acquisition card to the spectral compensation module in real time based on the deviation between the demodulation result and the expected value. The spectral compensation module adjusts the laser light intensity entering the photoelectric detection module according to the control electrical signal, thereby adjusting the demodulation result read by the data acquisition card in real time in the next moment, realizing the closed-loop negative feedback control function. The control computer stores the calculated control electrical signals and integrates them into a sequence.

[0056] The initial state of the spectral compensation module is set to 0% loss, the response speed is 2s, and the sampling rate of the data acquisition card is 0.5Hz.

[0057] Step 5, optimize spectral compensation effect: The control module works in the first working mode and adjusts the corresponding stored electrical signal sequence according to the deviation between the measured background spectrum and the expected value. The data acquisition card outputs the control electrical signal according to the adjusted control electrical signal sequence to complete the acquisition of background spectral data. Repeat this step until the deviation between the background spectrum and the expected value is less than the acceptable deviation.

[0058] In this embodiment of the invention, a proportional-integral-derivative control method is used, and the background spectrum obtained by repeating step 5 less than 10 times is obtained in which the deviation from the expected value is less than an acceptable deviation.

[0059] Step 6, Measure the sample spectrum: Fix the sample to be tested on the sample stage and let the spectral compensation module work in the first working mode according to the control electrical signal sequence finally obtained in step 5.

[0060] Step 7, calculate the laser absorption spectrum of the sample to be tested: The control module processes the background spectrum and the sample spectrum to obtain the laser absorption spectrum of the sample to be tested; the background spectrum is closer to the measurement upper limit of the photoelectric detection module than before spectral compensation, thereby reducing the dynamic range noise, detector noise and shot noise of the system, and improving the signal-to-noise ratio of the laser absorption spectrum of the sample to be tested.

[0061] Contents not described in detail in this specification are prior art known to those skilled in the art. Although illustrative specific embodiments of the invention have been described above to facilitate understanding by those skilled in the art, it should be understood that the invention is not limited to the scope of the specific embodiments. Various modifications are readily apparent to those skilled in the art as long as they fall within the spirit and scope of the invention as defined and determined by the appended claims, and all inventions utilizing the concept of this invention are protected.

Claims

1. A laser absorption spectroscopy measurement system based on adaptive spectral compensation, characterized by, The system is composed of a light source module, a transmission module, a spectrum compensation module, a photoelectric detection module and a control module; The light source module is used for outputting laser with adjustable wavelength and an electrical signal synchronized with the laser output; The transmission module is used for transmitting the laser to a sample stage and then transmitting the laser emitted from the sample stage to the spectrum compensation module; The spectrum compensation module includes an adjustable slit and an electric displacement stage, the adjustable slit is installed on the electric displacement stage and fixes the slit width at the same size as the diameter of the laser beam entering the spectrum compensation module, the electric displacement stage receives a control electrical signal from the control module and adjusts the displacement according to the control electrical signal, thereby adjusting the shielding ratio of the adjustable slit to the laser beam and adjusting the laser light intensity entering the photoelectric detection module; The photoelectric detection module is used for converting the received laser light intensity value into a data electrical signal and transmitting it to the control module; The control module is connected with the light source module and the photoelectric detection module, used for calculating the required control electrical signal according to the data electrical signal and transmitting it to the spectrum compensation module, thereby realizing the closed-loop negative feedback control function, making the background spectrum closer to the upper limit of the measurement of the photoelectric detection module as a whole, thereby reducing the dynamic range noise, detector noise and shot noise of the system and improving the signal-to-noise ratio of the system; at the same time, the control module is also used for data processing of the data electrical signal and calculating the laser absorption spectrum.

2. The adaptive spectral compensation based laser absorption spectroscopy measurement system of claim 1, wherein, The light source module includes a power supply, a laser driver, a temperature controller and a laser tube; the power supply is used for providing energy for the laser driver and the temperature controller; the laser driver is used for controlling the laser emission, the laser driver and the temperature controller are used together for controlling the scanning speed and scanning range of the center wavelength of the laser and maintaining stable laser output; the laser tube is used for outputting laser.

3. The adaptive spectral compensation based laser absorption spectroscopy measurement system of claim 1, wherein, The transmission module includes an off-axis parabolic mirror one, a sample stage and an off-axis parabolic mirror two; the off-axis parabolic mirror one is used for converging the laser to the sample stage; the sample stage is used for fixing the sample to be measured; the off-axis parabolic mirror two is used for collimating the laser emitted from the sample stage and making the laser enter the spectrum compensation module.

4. The adaptive spectral compensation based laser absorption spectroscopy measurement system of claim 1, wherein, The spectrum compensation module can also be replaced by a galvanometer and other similar devices that can quickly flip, the galvanometer is used for adjusting the transmission direction of the laser entering the spectrum compensation module, thereby adjusting the shielding ratio in space of the laser before entering the photoelectric detection module, the response speed of the galvanometer is usually faster than that of the electric displacement stage, which can improve the spectral scanning speed and spectral resolution of the system.

5. The adaptive spectral compensation based laser absorption spectroscopy measurement system of claim 1, wherein, The photoelectric detection module includes an off-axis parabolic mirror three and a photoelectric conversion device; the off-axis parabolic mirror three is used for converging the laser emitted from the spectrum compensation module into the photoelectric conversion device.

6. The adaptive spectral compensation based laser absorption spectroscopy measurement system of claim 1, wherein, The control module comprises a lock-in amplifier, a data acquisition card and a control computer; the lock-in amplifier is used for demodulating the data electrical signal output by the photoelectric detection module; the data acquisition card is used for reading the demodulation result of the lock-in amplifier and the electrical signal output by the light source module in real time and transmitting to the control computer; The control computer is used for storing the demodulation result and integrating into spectral data, processing the background spectral data collected when the sample table is empty or a reference sample is placed thereon and the sample-loaded spectral data collected when a sample to be measured is placed on the sample table and obtaining the laser absorption spectrum; the control computer is also used for controlling the data acquisition card to output a control electrical signal used for controlling the spectral compensation module.

7. The adaptive spectral compensation based laser absorption spectroscopy measurement system of claim 6, wherein, The control module has two working modes which can be switched, in the first working mode, the control computer lets the data acquisition card output the control electrical signal to complete the collection of the background spectral data or the sample-loaded spectral data according to the pre-written setting; in the second working mode, the control computer calculates the control electrical signal to be transmitted to the spectral compensation module by the data acquisition card at the next moment according to the deviation of the demodulation result from the expected value, and the spectral compensation module adjusts the laser intensity entering the photoelectric detection module according to the control electrical signal, thereby adjusting the demodulation result read by the data acquisition card in real time at the next moment, to realize the closed-loop negative feedback control function.

8. A method of laser absorption spectroscopy based on adaptive spectral compensation, characterized in that The laser absorption spectrum measurement system based on adaptive spectral compensation according to any one of claims 1-7 is executed, and the laser absorption spectrum measurement method based on adaptive spectral compensation comprises the following steps: (1) background spectral measurement preparation, setting the expected value of the background spectral amplitude and the acceptable deviation in the control module, cleaning the sample table and placing a reference sample or leaving the sample table empty according to the requirement, and setting the spectral compensation module in the initial state; (2) turning on the light source module, the light source module outputs laser and lets the center wavelength of the laser scan according to the set scanning speed and scanning range; (3) measuring the light intensity value, the laser output by the light source module enters the photoelectric detection module through the transmission module and the spectral compensation module, and the photoelectric detection module converts the received laser light intensity value into a data electrical signal and transmits it to the control module; (4) adaptive spectral compensation, the control module calculates the control electrical signal to be transmitted to the spectral compensation module at the next moment according to the deviation of the data electrical signal from the expected value in real time, the spectral compensation module adjusts the laser intensity entering the photoelectric detection module according to the control electrical signal, thereby adjusting the data electrical signal received by the control module at the next moment, to realize the closed-loop negative feedback control function; the control module stores the calculated control electrical signal and integrates it into a sequence; (5) optimizing the effect of spectral compensation, the control module adjusts the corresponding stored control signal sequence according to the deviation between the measured background spectrum and the expected value, and controls the spectral compensation module according to the adjusted control signal sequence to complete the acquisition of new background spectrum data; repeat this step until the deviation between the background spectrum and the expected value is less than the acceptable deviation; (6) measuring the sample-loaded spectrum, fixing the sample to be measured on the sample table, and allowing the control module to control the spectral compensation module according to the control signal sequence finally obtained in step 5; (7) calculating the laser absorption spectrum of the sample to be measured, and obtaining the laser absorption spectrum of the sample to be measured by data processing of the background spectrum and the sample-loaded spectrum through the control module; the background spectrum is closer to the measurement upper limit of the photoelectric detection module as a whole compared with before the spectral compensation, thereby reducing the dynamic range noise, the detector noise and the shot noise of the system, and improving the signal-to-noise ratio of the laser absorption spectrum of the sample to be measured measured by the system.

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