Multi-component absorption spectrum detection device and method based on supercontinuum light source

Abstract

The invention relates to the technical field of laser spectrum and photoelectric detection, in particular to a multi-component absorption spectrum detection device and method based on a super-continuum light source, and aims to solve the problem of simultaneous high-sensitivity detection of multiple gas components in the prior art. The detection device comprises a supercontinuum light source, an acousto-optic modulator, an optical fiber collimator, a sample gas cell, a diffraction grating, a rotary displacement table, a quartz tuning fork detector, a data acquisition card and a computer control unit, the rotary displacement table rotates around the axis of the rotary displacement table; and the diffraction grating and the quartz tuning fork detector are fixedly arranged on the rotary displacement table.

Description

Technical Field

[0001] The present invention relates to the field of laser spectrum and photoelectric detection technology, and in particular to a multi-component absorption spectrum detection device and method based on a supercontinuum light source. Background Art

[0002] Quartz crystal oscillators have been widely used in stress sensors, pressure sensors, temperature sensors and other fields due to their small size, low power consumption and high frequency stability. In the field of spectroscopy, the quartz tuning fork inside the quartz crystal oscillator after removing the outer shell has the advantages of low cost, high Q factor and small size. As a new type of acoustic signal sensor and photodetector, it has been widely used in applications such as trace gas detection. In addition, the narrow response bandwidth and effective resonance mode characteristics of the quartz tuning fork help to effectively reduce background noise. In recent years, based on the photo-induced thermoelastic deformation and piezoelectric effect of the quartz tuning fork, the laser spectroscopy detection method of using the quartz tuning fork as a spectral signal detector with wide-band response has attracted the attention of more and more scholars. However, due to the discrete distribution characteristics of the fingerprint absorption line of the gas molecule and the limitation of the wavelength output range of the commonly used tunable narrow linewidth laser, usually a laser light source can only meet the spectral detection of a single molecule. Especially when selecting strong absorption lines, considering the limiting factors such as the volume, weight, power consumption and cost of the spectral system, it is still a huge challenge to achieve simultaneous high-sensitivity detection of multiple gas components. Summary of the invention

[0003] In view of this, the purpose of the present invention is to propose a multi-component absorption spectrum detection device and method based on a supercontinuum light source to solve the problem of achieving simultaneous high-sensitivity detection of multiple gas components in the prior art.

[0004] Based on the above purpose, the present invention provides a multi-component absorption spectrum detection device based on a supercontinuum light source, the device comprises a supercontinuum light source, an acousto-optic modulator, an optical fiber collimator, a sample gas pool, a diffraction grating, a rotation stage, a quartz tuning fork detector, a data acquisition card and a computer control unit; the rotation stage rotates around its own axis; the diffraction grating and the quartz tuning fork detector are fixedly arranged on the rotation stage; the detection steps of the detection device are: the supercontinuum light source emits a laser, the laser enters the acousto-optic modulator, the acousto-optic modulator performs light intensity pulse modulation on the laser, the modulated laser enters the optical fiber collimator, the optical fiber collimator collimates the obtained laser, the collimated laser irradiates the sample gas pool, the sample gas pool is used to store the gas to be measured, the laser penetrates the sample gas pool and irradiates the diffraction grating, by rotating the rotation stage, the incident angle of the laser on the diffraction grating is adjusted, so that the laser reflected by the diffraction grating is irradiated on the fork arm of the quartz tuning fork detector; the quartz tuning fork is connected to the signal input end of the data acquisition card; the signal output end of the data acquisition card is connected to the computer control unit.

[0005] As a further improvement of the present application, an aperture stop is further provided on the rotary translation stage between the diffraction grating and the quartz tuning fork.

[0006] As a further improvement of the present application, a focusing lens is further provided on the rotational translation stage between the aperture diaphragm and the quartz tuning fork, the aperture diaphragm, the focusing lens and the quartz tuning fork are in a straight line, and an extension of the straight line penetrates the diffraction grating.

[0007] As a further improvement of the present application, both ends of the sample gas pool are light-transmitting windows.

[0008] As a further improvement of the present application, the sample gas cell is a single-pass absorption cell or a multi-pass absorption cell.

[0009] As a further improvement of the present application, the spectrum range of the laser emitted by the supercontinuum light source is from 470nm to 2200nm, covering the visible light region and the near-infrared region.

[0010] As a further improvement of the present application, the diffraction grating is a reflective ruled diffraction grating.

[0011] As a further improvement of the present application, the modulation frequency of the acousto-optic modulator is consistent with the intrinsic resonance frequency of the quartz tuning fork.

[0012] A detection method of a multi-component absorption spectrum detection device based on a supercontinuum light source is:

[0013] S1, the sample gas pool is not put into the gas to be tested, and then the detection step is performed, the data acquisition card obtains initial data, and transmits the initial data to the computer control unit;

[0014] S2, the sample gas pool is put into the gas to be tested, and then a detection step is performed, the data acquisition card obtains comparative data, and transmits the comparative data to the computer control unit;

[0015] S3, the computer control unit compares the comparison data with the initial data to obtain spectrum data of sample gas absorption;

[0016] S4, the computer control unit calculates the concentration of the sample gas by obtaining the spectrum data absorbed by the sample gas.

[0017] Beneficial effects of the present invention:

[0018] The present application proposes a multi-component absorption spectrum detection device and method based on a supercontinuum light source, which combines a supercontinuum light source, an acousto-optic modulator, a diffraction grating and a quartz tuning fork detector to achieve efficient detection of multi-component gases. The supercontinuum light source provides a broadband spectrum covering the absorption lines of multiple gas molecules. The laser beam is amplitude modulated by the acousto-optic modulator, and the diffraction grating is used to tune the wavelength of the supercontinuum light source. When the modulated light beam passes through a sample gas pool containing multiple gases, each gas produces an absorption effect in its specific fingerprint area. The quartz tuning fork detector performs photoelectric conversion and can simultaneously respond to photothermal signals in a wide band range. After subsequent processing by a computer control unit, the separation of the spectral signals of each component and the inversion of gas concentration are finally achieved in combination with the standard absorption profiles of each molecule. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are only for the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 The present invention is a schematic structural diagram of a multi-component absorption spectrum detection device based on a supercontinuum light source according to an embodiment of the present invention.

[0021] The markings in the figure are:

[0022] 1. Supercontinuum light source; 2. Acousto-optic modulator; 3. Fiber collimator; 4. Sample gas cell; 5. Diffraction grating; 6. Rotary translation stage; 7. Aperture diaphragm; 8. Focusing lens; 9. Quartz tuning fork detector; 10. Data acquisition card; 11. Computer control unit. DETAILED DESCRIPTION

[0023] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments.

[0024] It should be noted that, unless otherwise defined, the technical terms or scientific terms used in the present invention should be understood by people with ordinary skills in the field to which the present invention belongs. The "first", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0025] like Figure 1 As shown, a multi-component absorption spectrum detection device based on a supercontinuum light source includes a supercontinuum light source 1, an acousto-optic modulator 2, a fiber collimator 3, a sample gas pool 4, a diffraction grating 5, a rotation stage 6, a quartz tuning fork detector 9, a data acquisition card 10 and a computer control unit 11; the rotation stage 6 rotates around its own axis; the diffraction grating 5 and the quartz tuning fork detector 9 are fixedly arranged on the rotation stage 6. The quartz tuning fork 9 is connected to the signal input end of the data acquisition card 10; and the signal output end of the data acquisition card 10 is connected to the computer control unit 11.

[0026] The detection steps of the detection device are as follows: the supercontinuum light source 1 emits a laser, the laser enters the acousto-optic modulator 2, the acousto-optic modulator 2 performs light intensity pulse modulation on the laser, the modulated laser enters the fiber collimator 3, the fiber collimator 3 collimates the obtained laser, the collimated laser irradiates the sample gas pool 4, the sample gas pool 4 is used to store the gas to be tested, the laser penetrates the sample gas pool 4 and then irradiates the diffraction grating 5, and by rotating the rotary translation stage 6, the incident angle of the laser on the diffraction grating 5 is adjusted so that the laser reflected by the diffraction grating 5 is irradiated onto the fork arm of the quartz tuning fork detector 9.

[0027] Specifically, the rotary translation stage 6 realizes angular rotation through electric control, and achieves an adjustment accuracy of 30urad within a rotation range of 360°.

[0028] The supercontinuum light source 1 provides a broadband spectrum covering the absorption lines of multiple gas molecules. The laser beam is amplitude modulated by the acousto-optic modulator 2, and the diffraction grating 5 is used to tune the wavelength of the supercontinuum light source 1. When the modulated light beam passes through the sample gas pool 4 containing multiple gases, each gas produces an absorption effect in its specific fingerprint area. The quartz tuning fork detector 9 performs photoelectric conversion and can simultaneously respond to photothermal signals in a wide band range. After subsequent processing by the computer control unit 11, the separation of the spectral signals of each component and the inversion of gas concentration are finally achieved in combination with the standard absorption profiles of each molecule. The measurement of gas concentration is achieved.

[0029] The multi-component gas concentration inversion method uses a multiple linear regression algorithm based on direct absorption spectroscopy theory. The multiple linear regression model can be expressed as:

[0030] Y=α+β 1 X 1 +β 2 X 2 +…+β t X t +ε;

[0031] Among them, Y is the dependent variable, X 1 …X n is the independent variable, β 0 …β t is an unknown quantity. ε is a random error that satisfies the normal distribution The goal of multiple linear regression is to find the best coefficient β 0 …β t Minimize the difference between the model's predicted value and the actual observed value. This difference is usually quantified by the least squares method.

[0032] Assume {(Y i ,X i1 ,…,X it ), i=1,…,t} are observed values, at this time, α, β 0 …β t , the least squares estimate of σ is Among them, b 1 …b t Solve the following system of equations:

[0033]

[0034] in:

[0035]

[0036] When the absorption spectrum signal Y measured by the quartz tuning fork of the quartz tuning fork detector 9 and the standard spectrum lines X of various gas components are known, the above formula is used to calculate b1 …b t That is the proportional coefficient of each component, and then substitute it into a=Yb 1 X 1 -…-b t X t The formula gives α, b 1 …b t , The regression equation can be established. The concentration value of each component gas can be solved according to its respective proportional coefficient combined with the standard spectrum concentration value.

[0037] In order to filter stray light and scattered light, an aperture stop 7 is further provided on the rotary translation stage 6 between the diffraction grating 5 and the quartz tuning fork detector 9 .

[0038] A focusing lens 8 is also provided on the rotational translation stage 6 between the aperture diaphragm 7 and the quartz tuning fork detector 9 for concentrating the emitted laser so that the optical signal obtained by the quartz tuning fork 9 is stronger and more concentrated. The aperture diaphragm 7, the focusing lens 8 and the quartz tuning fork detector 9 are in a straight line, and the extension line of the straight line penetrates the diffraction grating 5.

[0039] Both ends of the sample gas pool 4 are light-transmitting windows.

[0040] The sample gas cell 4 is a single-pass absorption cell with a half optical path of <1 m, or a multi-pass absorption cell with an optical path of >10 m.

[0041] The spectrum range of the laser emitted by the supercontinuum light source 1 is from 470nm to 2200nm, covering the visible light region and the near-infrared region. The optical power reaches 800mW. In this wide band, a variety of gas components can be effectively detected. These include water vapor, carbon dioxide, carbon monoxide, methane, acetylene, ammonia, nitrogen dioxide, hydrogen sulfide and nitric oxide gases, each of which has a strong absorption characteristic in this spectral range. Among them, water vapor has multiple strong absorption bands in the near-infrared region, especially around 1300nm and 1900nm; methane shows a relatively obvious absorption characteristic at about 1650nm, with a line intensity of about 1.52E-21cm -1 / (molecule·cm -2 ); Nitrogen dioxide has significant absorption characteristics in the blue part of the visible spectrum; Acetylene has a strong absorption band near 1550nm, with a line intensity of about 1.34E-20cm -1 / (molecule·cm -2). Other gases such as carbon monoxide, ammonia, hydrogen sulfide and nitric oxide also have their own absorption characteristics in the same band. Although their absorption intensities and wavelength positions are different, they can all be effectively detected within this spectral range. The absorption characteristics of these gases make supercontinuum light sources an ideal choice for multi-component gas detection.

[0042] During the absorption process of the interaction between light and gas molecules, the change in the light intensity of the light source follows the Lambert-Beer law:

[0043] I t (v)=I 0 (v)exp(-a(v)·L)

[0044] In the above formula, v is the wave number of the laser [cm -1 ];

[0045] I t (v) -- the transmitted light intensity after the light passes through the gaseous absorption medium [nW];

[0046] I 0 (v) --initial incident (reference) light intensity [nW];

[0047] a(v)--absorption coefficient at a specific wavelength [cm -1 ];

[0048] L – effective length of laser light through gas absorption medium [cm].

[0049] The expression of the absorption coefficient is as follows:

[0050] a(v)=φ(vv 0 )·S i (T)·P·X j

[0051] In the above formula, φ(vv 0 )--Normalized absorption linear function ∫φ(vv 0) dv = 1 [cm];

[0052] S i (T)--absorption line intensity [cm -2 ·atm -1 ];

[0053] P--total gas pressure [atm];

[0054] X j --The volume ratio of absorbed gas to total volume, that is, the concentration of absorbed gas.

[0055] In the actual signal processing process, by numerically integrating the absorption profile, the integral absorption area expression can be obtained as:

[0056]

[0057] In the above formula: σ(v)--absorption cross section [cm 2 ];

[0058] N j (T,P)--Molecular density of absorbing gas [molecule / cm -3 ];

[0059] --Absorption line intensity [cm -1 / (molecule·cm -2 )];

[0060] A(v)--absorbance at a specific wavelength;

[0061] L – effective length of laser light through gas absorption medium [cm].

[0062] The diffraction grating 5 is a reflective ruled diffraction grating, and its diffraction wavelength range covers ultraviolet to mid-infrared, and is customized according to the wavelength range of the supercontinuum light source 1 used.

[0063] The diffraction grating 5 is based on the principle of light diffraction, that is, when light passes through a series of regularly arranged grating grooves, light of different wavelengths will be diffracted to different angles, thereby achieving the function of tuning the wavelength.

[0064] According to Fraunhofer diffraction theory, when a beam of parallel light is projected vertically onto the grating plane, the light is diffracted through each slit, and the diffracted light from all slits interferes with each other. The diffracted light after diffraction by the grating is focused onto the surface of the quartz tuning fork detector 9 through a lens. The position of the diffraction bright fringe can be obtained by Fraunhofer diffraction theory:

[0065] dsinθ=mλ, m=±1,±2...,±n.

[0066] In the above formula: θ--diffraction angle;

[0067] λ--wavelength;

[0068] m--diffraction order;

[0069] d--grating constant.

[0070] The modulation frequency of the acousto-optic modulator 2 is consistent with the intrinsic resonance frequency of the quartz tuning fork 9 .

[0071] A detection method of a multi-component absorption spectrum detection device based on a supercontinuum light source is:

[0072] S1, the sample gas pool 4 is not put into the gas to be tested, and then the detection step is performed, the data acquisition card 10 obtains initial data, and transmits the initial data to the computer control unit 11;

[0073] S2, the sample gas pool 4 is put into the gas to be tested, and then the detection step is performed, the data acquisition card 10 obtains the comparison data, and transmits the comparison data to the computer control unit 11;

[0074] S3, the computer control unit 11 compares the comparison data with the initial data to obtain spectrum data of sample gas absorption;

[0075] S4, the computer control unit 11 calculates the concentration of the sample gas by obtaining the spectrum data absorbed by the sample gas.

[0076] Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of the present invention (including the claims) is limited to these examples. Under the concept of the present invention, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of the different aspects of the present invention as described above, which are not provided in detail for the sake of simplicity.

[0077] The present invention is intended to cover all such substitutions, modifications and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A multi-component absorption spectrum detection device based on a supercontinuum light source, characterized in that: The device comprises a supercontinuum light source (1), an acousto-optic modulator (2), a fiber collimator (3), a sample gas pool (4), a diffraction grating (5), a rotary displacement stage (6), a quartz tuning fork detector (9), a data acquisition card (10) and a computer control unit (11); The rotary translation platform (6) rotates around its own axis; The diffraction grating (5) and the quartz tuning fork detector (9) are fixedly arranged on the rotary displacement stage (6); The detection steps of the detection device are as follows: the supercontinuum light source (1) emits laser light, the laser light enters the acousto-optic modulator (2), the acousto-optic modulator (2) performs light intensity pulse modulation on the laser light, the modulated laser light enters the optical fiber collimator (3), the optical fiber collimator (3) collimates the obtained laser light, the collimated laser light irradiates the sample gas pool (4), the sample gas pool (4) is used to store the gas to be tested, the laser light penetrates the sample gas pool (4) and then irradiates the diffraction grating (5), and the incident angle of the laser light on the diffraction grating (5) is adjusted by rotating the rotary displacement stage (6), so that the laser light reflected by the diffraction grating (5) is irradiated onto the fork arm of the quartz tuning fork detector (9); The quartz tuning fork (9) is connected to the signal input end of the data acquisition card (10); the signal output end of the data acquisition card (10) is connected to the computer control unit (11).

2. The multi-component absorption spectrum detection device based on a supercontinuum light source according to claim 1, characterized in that: An aperture stop (7) is also provided on the rotary displacement stage (6) between the diffraction grating (5) and the quartz tuning fork (9).

3. The multi-component absorption spectrum detection device based on a supercontinuum light source according to claim 2, characterized in that: A focusing lens (8) is also provided on the rotational translation stage (6) between the aperture diaphragm (7) and the quartz tuning fork (9); the aperture diaphragm (7), the focusing lens (8) and the quartz tuning fork (9) are on a straight line, and an extension of the straight line penetrates the diffraction grating (5).

4. The multi-component absorption spectrum detection device based on a supercontinuum light source according to claim 1, characterized in that: Both ends of the sample gas pool (4) are light-transmitting windows.

5. The multi-component absorption spectrum detection device based on a supercontinuum light source according to claim 1, characterized in that: The sample gas cell (4) is a single-pass absorption cell or a multi-pass absorption cell.

6. The multi-component absorption spectrum detection device based on a supercontinuum light source according to claim 1, characterized in that: The spectrum range of the laser emitted by the supercontinuum light source (1) is from 470nm to 2200nm, covering the visible light region and the near infrared region.

7. The multi-component absorption spectrum detection device based on a supercontinuum light source according to claim 1, characterized in that: The diffraction grating (5) is a reflective ruled diffraction grating.

8. The multi-component absorption spectrum detection device based on a supercontinuum light source according to claim 1, characterized in that: The modulation frequency of the acousto-optic modulator (2) is consistent with the intrinsic resonance frequency of the quartz tuning fork (9).

9. The detection method according to any one of claims 1 to 8, characterized in that: S1, the sample gas pool (4) is not put into the gas to be tested, and then a detection step is performed, the data acquisition card (10) obtains initial data, and transmits the initial data to the computer control unit (11); S2, the sample gas pool (4) is put into the gas to be tested, and then a detection step is performed, the data acquisition card (10) obtains comparison data, and transmits the comparison data to the computer control unit (11); S3, the computer control unit (11) compares the comparison data with the initial data to obtain spectrum data of sample gas absorption; S4, the computer control unit (11) calculates the concentration of the sample gas by obtaining the spectrum data of the sample gas absorption.

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