CN114112925A - Liquid trace detection device and method - Google Patents
Liquid trace detection device and method Download PDFInfo
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- 238000001514 detection method Methods 0.000 title claims abstract description 46
- 239000007788 liquid Substances 0.000 title claims abstract description 31
- 238000000034 method Methods 0.000 title abstract description 19
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- 238000006243 chemical reaction Methods 0.000 claims description 21
- 238000006073 displacement reaction Methods 0.000 claims description 18
- 230000003287 optical effect Effects 0.000 claims description 17
- 238000013500 data storage Methods 0.000 claims description 10
- 238000010521 absorption reaction Methods 0.000 claims description 8
- 238000010438 heat treatment Methods 0.000 claims description 6
- 238000004093 laser heating Methods 0.000 claims description 6
- 230000005284 excitation Effects 0.000 claims description 5
- 239000000284 extract Substances 0.000 claims description 3
- 238000010606 normalization Methods 0.000 claims description 3
- 238000005259 measurement Methods 0.000 claims 1
- 230000000694 effects Effects 0.000 abstract description 16
- 238000004454 trace mineral analysis Methods 0.000 abstract description 5
- 238000000605 extraction Methods 0.000 abstract description 4
- 239000000523 sample Substances 0.000 description 73
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 17
- 238000002474 experimental method Methods 0.000 description 7
- RBTBFTRPCNLSDE-UHFFFAOYSA-N 3,7-bis(dimethylamino)phenothiazin-5-ium Chemical compound C1=CC(N(C)C)=CC2=[S+]C3=CC(N(C)C)=CC=C3N=C21 RBTBFTRPCNLSDE-UHFFFAOYSA-N 0.000 description 6
- 229960000907 methylthioninium chloride Drugs 0.000 description 6
- 238000004458 analytical method Methods 0.000 description 5
- 238000010586 diagram Methods 0.000 description 5
- 230000008569 process Effects 0.000 description 5
- 239000012488 sample solution Substances 0.000 description 5
- 125000000325 methylidene group Chemical group [H]C([H])=* 0.000 description 3
- PCTMTFRHKVHKIS-BMFZQQSSSA-N (1s,3r,4e,6e,8e,10e,12e,14e,16e,18s,19r,20r,21s,25r,27r,30r,31r,33s,35r,37s,38r)-3-[(2r,3s,4s,5s,6r)-4-amino-3,5-dihydroxy-6-methyloxan-2-yl]oxy-19,25,27,30,31,33,35,37-octahydroxy-18,20,21-trimethyl-23-oxo-22,39-dioxabicyclo[33.3.1]nonatriaconta-4,6,8,10 Chemical compound C1C=C2C[C@@H](OS(O)(=O)=O)CC[C@]2(C)[C@@H]2[C@@H]1[C@@H]1CC[C@H]([C@H](C)CCCC(C)C)[C@@]1(C)CC2.O[C@H]1[C@@H](N)[C@H](O)[C@@H](C)O[C@H]1O[C@H]1/C=C/C=C/C=C/C=C/C=C/C=C/C=C/[C@H](C)[C@@H](O)[C@@H](C)[C@H](C)OC(=O)C[C@H](O)C[C@H](O)CC[C@@H](O)[C@H](O)C[C@H](O)C[C@](O)(C[C@H](O)[C@H]2C(O)=O)O[C@H]2C1 PCTMTFRHKVHKIS-BMFZQQSSSA-N 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
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- 239000000126 substance Substances 0.000 description 2
- 230000001133 acceleration Effects 0.000 description 1
- 238000003384 imaging method Methods 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 238000005305 interferometry Methods 0.000 description 1
- 230000031700 light absorption Effects 0.000 description 1
- 230000004044 response Effects 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- 238000002834 transmittance Methods 0.000 description 1
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- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/171—Systems in which incident light is modified in accordance with the properties of the material investigated with calorimetric detection, e.g. with thermal lens detection
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- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/171—Systems in which incident light is modified in accordance with the properties of the material investigated with calorimetric detection, e.g. with thermal lens detection
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Abstract
Aiming at the limitation of the prior art, the invention provides a liquid trace detection device, which generates a photo-thermal self-mixing signal by modulating the length of an external cavity, combines the photo-thermal self-mixing signal to envelop amplitude extraction, measures the self-mixing signal envelop amplitude change caused by the light beam central light intensity change caused by the sample thermal lens effect, and realizes the trace analysis of a sample by utilizing the linear relation between the photo-thermal self-mixing parameter and the sample concentration; because the detection is realized by using the single light beam optically coupled between the feedback light and the cavity, compared with the traditional photothermal lens analyzer, the analyzer is small and compact and is convenient to use; compared with the traditional method for directly measuring the change of the central light intensity of the light beam, the method has the advantages that the change of the central light intensity of the light beam is converted into the change of the envelope amplitude of the self-mixing signal, and the self-mixing signal stripes have the effect of suppressing electrical noise, so that the detection limit of an instrument is favorably improved.
Description
Technical Field
The invention relates to the technical field of trace analysis, in particular to a photothermal spectrometer technology, and more particularly relates to a liquid trace detection device and method.
Background
The self-mixing interferometer is a single-light path interferometer integrating a light source, an interferometer and a detector. The self-mixing interference effect is a new technology with high sensitivity in the detection field, can measure various physical parameters including displacement, speed, acceleration, flow, refractive index, laser line width and the like, and is also applied to the aspects of biomedicine, imaging and the like. When laser emitted by the laser enters the laser cavity after being reflected or scattered by an external object, light in the cavity and feedback light generate self-mixing interference, and the light intensity and wavelength of the output light of the laser are changed. Compared with the traditional interferometer principle, the two interference signal waveforms are similar in shape and identical in fringe resolution, but the laser self-mixing interferometer has the advantages of being simple in light path, free of an additional filter and the like.
For example, the Chinese invention patent with publication date of 2021.07.09: photothermal interferometry is shown to be a highly sensitive method for measuring the light absorption and thermal properties of a sample by photothermal lens analysis. The thermal lens effect is that when laser emitted by a laser passes through a medium, because the energy of the laser beam is in Gaussian distribution, the medium absorbs the energy of the laser to generate a radial temperature gradient, and further a radial refractive index gradient is generated, so that a lens-like effect is formed. The photothermal lens analysis method has two to three higher detection limits than the conventional transmission analysis method, so that the photothermal lens analysis method has wide application in the field of trace analysis. Although the concentration of the detectable substance is low at present, designing a photothermal lens analyzer using low-power laser to achieve high-sensitivity detection is still an important task, and the miniaturization of the analyzer is also a problem to be solved.
Disclosure of Invention
Aiming at the limitation of the prior art, the invention provides a liquid trace detection device and a method, and the technical scheme adopted by the invention is as follows:
a liquid trace detection apparatus comprising: the system comprises a photo-thermal self-mixing light path module, an external cavity length modulation module and a photoelectric signal acquisition, conversion and processing module;
the photo-thermal self-mixing light path module comprises a laser, a light switch, a sample tank and a plane mirror which are sequentially arranged along the same light path when in use;
the external cavity length modulation module comprises a signal generator and a micro displacement table controlled by the signal generator;
the plane mirror is arranged on the micro-displacement table and is displaced along with the operation of the micro-displacement table; the photoelectric signal acquisition conversion processing module is connected with a rear light outlet of the laser and used for acquiring a photo-thermal self-mixing signal reflected to the laser, acquiring photo-thermal self-mixing parameters of a sample to be detected by extracting an envelope amplitude of the photo-thermal self-mixing signal, and measuring the solution concentration of the sample to be detected according to the photo-thermal self-mixing parameters.
Compared with the prior art, the method generates the photo-thermal self-mixing signal by modulating the length of the external cavity, combines the photo-thermal self-mixing signal envelope amplitude extraction, measures the self-mixing signal envelope amplitude change caused by the light beam central light intensity change caused by the sample thermal lens effect, and realizes the trace analysis of the sample by utilizing the linear relation between the photo-thermal self-mixing parameter and the sample concentration; because the detection is realized by using the single light beam optically coupled between the feedback light and the cavity, compared with the traditional photothermal lens analyzer, the analyzer is small and compact and is convenient to use; compared with the traditional method for directly measuring the change of the central light intensity of the light beam, the method has the advantages that the change of the central light intensity of the light beam is converted into the change of the envelope amplitude of the self-mixing signal, and the self-mixing signal stripes have the effect of suppressing electrical noise, so that the detection limit of an instrument is favorably improved.
As a preferred scheme, the photoelectric signal acquisition, conversion and processing module comprises a photodiode, an operational amplifier, a data storage medium and a computer; the photodiode is arranged at a rear light outlet of the laser and is connected with the operational amplifier; the operational amplifier is connected with the data storage medium; the data storage medium is connected with the computer.
Preferably, the laser is a gaussian beam laser.
Preferably, in use, the micro-displacement stage is continuously sinusoidally vibrated in response to the sinusoidal signal generated by the signal generator.
As a preferable scheme, the liquid trace amount detection device satisfies the following conditions:
b2>>L2；
b2>>d2；
L>l；
wherein b is a confocal parameter of the laser, L is a distance from the laser to the plane mirror, d is a distance from the laser to a sample to be detected, and L is a length of the sample.
As a preferable scheme, the photoelectric signal acquisition, conversion and processing module extracts the envelope amplitude of the photo-thermal self-mixing signal by using a maximum detection algorithm in the process of signal processing.
As a preferable scheme, in the signal processing process, the photoelectric signal acquisition, conversion and processing module obtains the photothermal self-mixing parameter s (m) of the sample to be detected according to the following formula:
wherein, | Δ PF0I is the envelope amplitude of the initial moment of the Mth laser heating period; | Δ PFt(at tt1)And | is the envelope amplitude at the moment when the mth laser heating period t is t 1.
As a preferable scheme, in the signal processing process, the photoelectric signal acquisition, conversion and processing module obtains the solution concentration C of the sample to be detected according to the following formula:
wherein S (M) represents photothermalSelf-mixing parameters; k1、K2And K3Are all preset constants; dn/dT is the coefficient of change of the refractive index of the sample to be detected along with the temperature; p is the output optical power of the laser; l is the length of the sample; the Joule coefficient J is 4.18; k is the thermal conductivity of the sample to be detected; omega0The radius of a beam generated by the laser at a light outlet of the laser; t is t1Is the excitation time length; t is tcThe photothermal time constant.
Further, constant K3Set by the following formula:
wherein alpha is0The absorption coefficient of the sample to be detected at a solution concentration of 0 is shown.
The present invention also provides the following:
a liquid trace detection method based on the liquid trace detection device comprises the following steps:
s1, placing the cuvette containing the sample to be detected in the sample groove, and starting the laser and the optical switch to irradiate the sample to be detected for a period of time;
s2, collecting photo-thermal self-mixing signals, and extracting the photo-thermal self-mixing signals of the heating section after normalization processing;
and S3, extracting the envelope amplitude of the photo-thermal self-mixing signal to obtain photo-thermal self-mixing parameters of the sample to be detected, and measuring the solution concentration of the sample to be detected according to the photo-thermal self-mixing parameters.
Drawings
FIG. 1 is a schematic view of an overview of a liquid trace detection apparatus provided in an embodiment of the present invention;
FIG. 2 is a schematic diagram of the detailed structure and connection of a liquid trace detection device according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a sample thermal lens formation;
FIG. 4 is an example of the variation of the external cavity light of the liquid trace detection device provided by the embodiment of the present invention;
FIG. 5 is a schematic diagram of the steps of the liquid trace detection method provided in example 3 of the present invention;
FIG. 6 is a graph of photothermal self-mixing signals of absolute ethanol in an experiment of example 3 according to the present invention;
FIG. 7 is a graph showing the variation of the envelope amplitude of the photo-thermal self-mixing signal of 8.0umol/L methylene blue ethanol solution in the experiment of example 3 according to the present invention;
FIG. 8 is a graph showing the relationship between different concentrations of methylene blue ethanol solutions and the amplitude variation in the experiment of example 3 according to the present invention;
description of the drawings: 1. the photo-thermal self-mixing light path module; 11. a laser; 12. an optical switch; 13. a sample tank; 14. a plane mirror; 2. an external cavity length modulation module; 21. a signal generator; 22. a micro-displacement stage; 3. a photoelectric signal acquisition, conversion and processing module; 31. a photodiode; 32. an operational amplifier; 33. a data storage medium; 34. and (4) a computer.
Detailed Description
The drawings are for illustrative purposes only and are not to be construed as limiting the patent;
it should be understood that the embodiments described are only some embodiments of the present application, and not all embodiments. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments in the present application without any creative effort belong to the protection scope of the embodiments in the present application.
The terminology used in the embodiments of the present application is for the purpose of describing particular embodiments only and is not intended to be limiting of the embodiments of the present application. As used in the examples of this application and the appended claims, the singular forms "a", "an", and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It should also be understood that the term "and/or" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items.
When the following description refers to the accompanying drawings, like numbers in different drawings represent the same or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present application. Rather, they are merely examples of apparatus and methods consistent with certain aspects of the application, as detailed in the appended claims. In the description of the present application, it is to be understood that the terms "first," "second," "third," and the like are used solely to distinguish one from another and are not necessarily used to describe a particular order or sequence, nor are they to be construed as indicating or implying relative importance. The specific meaning of the above terms in the present application can be understood by those of ordinary skill in the art as appropriate.
Further, in the description of the present application, "a plurality" means two or more unless otherwise specified. "and/or" describes the association relationship of the associated objects, meaning that there may be three relationships, e.g., a and/or B, which may mean: a exists alone, A and B exist simultaneously, and B exists alone. The character "/" generally indicates that the former and latter associated objects are in an "or" relationship. The invention is further illustrated below with reference to the figures and examples.
In order to solve the limitation of the prior art, the present embodiment provides a technical solution, and the technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments.
Example 1
Referring to fig. 1 and fig. 2, a liquid trace detection apparatus includes: the system comprises a photo-thermal self-mixing light path module 1, an external cavity length modulation module 2 and a photoelectric signal acquisition conversion processing module 3;
the photo-thermal self-mixing optical path module 1 comprises a laser 11, an optical switch 12, a sample tank 13 and a plane mirror 14 which are sequentially arranged along the same optical path when in use;
the external cavity length modulation module 2 comprises a signal generator 21 and a micro-displacement table 22 controlled by the signal generator 21;
the plane mirror 14 is arranged on the micro-displacement table 22 and is displaced along with the operation of the micro-displacement table 22; the photoelectric signal acquisition conversion processing module 3 is connected with a rear light outlet of the laser 11 and used for acquiring a photo-thermal self-mixing signal reflected to the laser 11, acquiring photo-thermal self-mixing parameters of a sample to be detected by extracting an envelope amplitude of the photo-thermal self-mixing signal, and measuring the solution concentration of the sample to be detected according to the photo-thermal self-mixing parameters.
Compared with the prior art, the method generates the photo-thermal self-mixing signal by modulating the length of the external cavity, combines the photo-thermal self-mixing signal envelope amplitude extraction, measures the self-mixing signal envelope amplitude change caused by the light beam central light intensity change caused by the sample thermal lens effect, and realizes the trace analysis of the sample by utilizing the linear relation between the photo-thermal self-mixing parameter and the sample concentration; because the detection is realized by using the single light beam optically coupled between the feedback light and the cavity, compared with the traditional photothermal lens analyzer, the analyzer is small and compact and is convenient to use; compared with the traditional method for directly measuring the change of the central light intensity of the light beam, the method has the advantages that the change of the central light intensity of the light beam is converted into the change of the envelope amplitude of the self-mixing signal, and the self-mixing signal stripes have the effect of suppressing electrical noise, so that the detection limit of an instrument is favorably improved.
Specifically, the solution provided by this embodiment is to find a linear relationship between the sample concentration and the amplitude variation by measuring the amplitude variation of the envelope of the self-mixing signal caused by the thermal lens effect of the sample.
In this embodiment, the laser is used as an excitation light source of the device, and can also be regarded as a high-sensitivity detection light source, and also used as a detector of the device; the light outlet of the laser is used as an equivalent diaphragm to limit the feedback light from entering the laser resonant cavity and realize paraxial detection. Laser emitted by the laser is modulated by the optical switch, passes through the sample tank containing a sample to be detected, is reflected by the planar mirror, passes through the sample tank again and then returns into the laser cavity, and the feedback light and the light in the cavity form a self-mixing interference effect. Meanwhile, referring to fig. 3, the micro-displacement stage drives the plane mirror to move, and the length of the external cavity changes to generate a self-mixing signal; when the laser passes through the sample to be detected, referring to fig. 4, the sample to be detected absorbs the energy of the laser to generate a radial temperature gradient, and further a radial refractive index gradient is generated, and the liquid sample is equivalent to a concave lens due to a negative thermo-optic coefficient. The laser gradually diverges along with the gradual formation of the thermal lens when passing through a sample to be detected, and the light intensity returned to the laser cavity after being limited by the light outlet of the laser is gradually reduced, so that the self-mixing interference effect is weakened, namely the self-mixing signal envelope amplitude is gradually reduced, and finally the photo-thermal self-mixing effect is formed.
The photoelectric signal acquisition conversion processing module 3 can use a LabVIEW program of a computer to complete signal processing contents such as signal extraction and the like for a platform.
Example 2
Referring to fig. 1 and 2, a liquid trace detection apparatus includes: the system comprises a photo-thermal self-mixing light path module 1, an external cavity length modulation module 2 and a photoelectric signal acquisition conversion processing module 3;
the photo-thermal self-mixing optical path module 1 comprises a laser 11, an optical switch 12, a sample tank 13 and a plane mirror 14 which are sequentially arranged along the same optical path when in use;
the external cavity length modulation module 2 comprises a signal generator 21 and a micro-displacement table 22 controlled by the signal generator 21;
the plane mirror 14 is arranged on the micro-displacement table 22 and is displaced along with the operation of the micro-displacement table 22; the photoelectric signal acquisition, conversion and processing module 3 is connected with a rear light outlet of the laser 11 and is used for acquiring a photo-thermal self-mixing signal reflected to the laser 11, acquiring photo-thermal self-mixing parameters of a sample to be detected by extracting an envelope amplitude of the photo-thermal self-mixing signal, and measuring the solution concentration of the sample to be detected according to the photo-thermal self-mixing parameters;
the photoelectric signal acquisition, conversion and processing module 3 comprises a photodiode 31, an operational amplifier 32, a data storage medium 33 and a computer 34; the photodiode 31 is arranged at a rear light outlet of the laser 11 and connected with the operational amplifier 32; the operational amplifier 32 is connected with the data storage medium 33; the data storage medium 33 is connected with the computer 34;
the laser 11 is a Gaussian beam laser;
in use, the micro-displacement stage 22 continuously oscillates sinusoidally according to the generated sinusoidal signal of the signal generator 21;
the liquid trace detection device meets the following conditions:
b2>>L2；
b2>>d2；
L>l；
wherein b is a confocal parameter of the laser 11, L is a distance from the laser 11 to the plane mirror 14, d is a distance from the laser 11 to a sample to be detected, and L is a length of the sample;
the photoelectric signal acquisition, conversion and processing module 3 extracts the envelope amplitude of the photo-thermal self-mixing signal by a maximum detection algorithm in the process of signal processing;
the photoelectric signal acquisition conversion processing module 3 obtains the solution concentration C of the sample to be detected according to the following formula in the signal processing process:
wherein S (M) represents a photothermal self-mixing parameter; k1、K2And K3Are all preset constants; dn/dT is the coefficient of change of the refractive index of the sample to be detected along with the temperature; p is the output optical power of the laser 11; l is the length of the sample; the Joule coefficient J is 4.18; k is the thermal conductivity of the sample to be detected; omega0The beam radius of the laser generated by the laser 11 at the light outlet of the laser 11; t is t1Is the excitation time length; t is tcIs the photo-thermal time constant;
constant K3Set by the following formula:
wherein alpha is0The absorption coefficient of the sample to be detected at a solution concentration of 0 is shown.
Specifically, the storage medium 33 may be implemented by a data acquisition card; the photodiode can convert a light intensity signal of a rear light outlet of the laser into a current signal, and then the current signal is connected with a data acquisition card through an operational amplifier, the data acquisition card is connected with a computer, the current signal is converted into a voltage signal and amplified, and the photo-thermal self-mixing signal acquisition is completed.
By adopting a Gaussian beam laser and a high-sensitivity laser resonant cavity, high-sensitivity detection can be realized by adopting a low-power laser, and the requirement of an instrument on laser power is further reduced.
The solution of the present embodiment will be further explained in principle:
when the concentration of the sample solution is 0, the ABCD rule describing propagation of a gaussian beam in optics is used, and for the gaussian beam, q is expressed when z at the laser light outlet is 0 plane0With a beam radius of omega0After passing through the sample, the light beam reflected by the plane mirror back to the plane where z is 0 can be expressed as:
wherein:
the beam radius at the location where the reflection surface z is 0 where the light is reflected back to the laser exit is ω2Can be expressed as:
wherein: λ is the wavelength of light, b is the confocal parameter of the laser, L is the distance from the laser to the plane mirror, nsIs the initial refractive index of the sample and l is the length of the sample.
The light beam fed back to the inner cavity has an equivalent transmittance of
By combining the three-mirror-cavity theoretical model, the output light power of the laser can be obtained as follows:
wherein: p0Is the laser output light power without light reflection, and m is the modulation coefficient.
Wherein: t is taThe laser passes through the sample, and the sample absorbs the corresponding transmission coefficient, LlaserIs the laser lumen length, r2Is the reflection coefficient of the front facet of the laser, r2extIs the reflection coefficient of the external flat mirror.
When the concentration of the sample solution is not 0, the sample absorbs energy of gaussian light, and the refractive index change caused by the absorption is:
wherein: dn/dT is the coefficient of change of the sample refractive index with temperature, and the sample absorption coefficient alpha is K2C + alpha, C is the sample concentration, K2The proportionality coefficient (which is a constant) of the absorption coefficient of the sample with the change of the sample concentration can be regarded as alpha is the absorption coefficient when the sample concentration is 0. J-4.18 is the Joule coefficient, tcIs the photothermal time constant and k is the thermal conductivity of the sample.
Using ABCD's law, for a gaussian beam, q is expressed when z is 0 plane0With a beam radius of omega0After passing through the sample to be measured, the light beam reflected by the plane mirror back to the plane where z is 0 can be expressed as:
wherein
Wherein: d is the distance from the laser to the sample; when laser with Gaussian distribution passes through a sample, the sample absorbs the energy of the laser to generate a radial temperature gradient and further generate a radial refractive index gradient, a liquid sample is equivalent to a concave lens due to a negative thermo-optic coefficient, and the variation amplitude of the focal length F of the lens is as follows:
wherein: t is t1Is the excitation time period.
When the concentration of the sample solution is not 0, the light beam passing through the sample and reflected by the plane mirror back to the plane where z is 0 can be expressed as:
at this time, the laser output optical power is expressed as:
combining equations (5) and (12) yields:
due to the arrangement of the invention b2>>L2,b2>>d2And L>l, obtaining:
thus, the photothermal self-mixing parameters can be defined as:
wherein: | Δ PF0I is the amplitude of the photo-thermal self-mixing signal at the initial time of the Mth laser heating period, | Δ PFt(at tt1)I is t-t of Mth laser heating period1The magnitude of the photo-thermal self-mixing signal at the moment.
The following can be obtained:
wherein: k1、K2And K3All are constants.
From equation (16), the photothermal self-mixing parameter is linear with the concentration of the sample solution.
As shown in fig. 5, when the optical switch is just turned on, there is no photothermal effect, and the amplitude of the photothermal self-mixing signal corresponds to | PF0L. When the laser is continuously irradiated, the amplitude value of the tail photo-thermal self-mixing signal of the heating section is corresponding to | PFt(at tt1)L. And (3) solving photo-thermal self-mixing parameters by extracting the amplitude of the photo-thermal self-mixing signal and utilizing a formula (15), and obtaining the trace detection of the sample solution according to a formula (16).
Example 3
A liquid trace detection method implemented based on the liquid trace detection device described in embodiment 1 or 2, please refer to fig. 5, which includes the following steps:
s1, placing the cuvette containing the sample to be detected in the sample groove 13, and starting the laser 11 and the optical switch 12 to irradiate the sample to be detected for a period of time;
s2, collecting photo-thermal self-mixing signals, and extracting the photo-thermal self-mixing signals of the heating section after normalization processing;
and S3, extracting the envelope amplitude of the photo-thermal self-mixing signal to obtain photo-thermal self-mixing parameters of the sample to be detected, and measuring the solution concentration of the sample to be detected according to the photo-thermal self-mixing parameters.
The protocol provided in this example will be described below with reference to specific experiments:
in the experiment, methylene blue substances with better absorption to light of 632.8nm are selected as samples for analysis, ethanol is used as a solvent, and methylene blue-ethanol solutions with different concentrations are prepared. The concentration of the prepared methylene blue-ethanol solution is 1umol/L-10 umol/L. During the experiment, 10 groups of photo-thermal self-mixing signals are collected for each concentration, the average value of amplitude variation is obtained, photo-thermal self-mixing parameters are calculated, and the linear relation between the concentration of the methylene blue-ethanol solution and the amplitude variation and the quantitative limit of detection are obtained.
In the experiment of this example, the frequency of the optical switch was set to 0.5Hz and the irradiation time was 2 minutes.
FIG. 6 shows a photo-thermal self-mixing signal diagram of 0umol/L methylene blue ethanol solution, i.e. a photo-thermal self-mixing signal diagram of absolute ethanol. From the figure, the photothermal self-mixing signal of the heating section has almost the same head amplitude and tail amplitude.
FIG. 7 is a graph showing the change in the envelope amplitude of the photo-thermal self-mixing signal of 8.0umol/L methylene blue ethanol solution. As can be seen from the figure, the photothermal self-mixing signal of the heating section has a maximum envelope amplitude due to the non-photothermal effect at the beginning. When Gaussian light continuously heats a sample, the sample absorbs light energy to form a thermal lens effect, the light beam is gradually diffused, the light intensity fed back to the inner cavity is gradually weakened, the feedback light modulation coefficient m is gradually reduced, and the photo-thermal self-mixing interference signal envelope is gradually reduced.
FIG. 8 is a graph of the linear relationship between the concentration of different concentrations of methylene blue ethanol solution and the photo-thermal self-mixing parameter.
It should be understood that the above-described embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the claims of the present invention.
Claims (10)
1. A liquid trace detection apparatus, comprising: the system comprises a photo-thermal self-mixing light path module (1), an external cavity length modulation module (2) and a photoelectric signal acquisition, conversion and processing module (3);
the photo-thermal self-mixing light path module (1) comprises a laser (11), a light switch (12), a sample groove (13) and a plane mirror (14) which are sequentially arranged along the same light path when in use;
the external cavity length modulation module (2) comprises a signal generator (21) and a micro displacement table (22) controlled by the signal generator (21);
the plane mirror (14) is arranged on the micro displacement table (22) and moves along with the operation of the micro displacement table (22); photoelectric signal gathers conversion processing module (3) and connects the back light-emitting window of laser instrument (11) for acquire reflect to laser instrument (11) light and heat are from the mixing signal, through extracting the envelope amplitude of light and heat from the mixing signal obtains to wait to detect the light and heat from the mixing parameter of sample, according to the light and heat is from mixing parameter measurement to wait to detect the solution concentration of sample.
2. The liquid trace detection device according to claim 1, wherein the photoelectric signal acquisition, conversion and processing module (3) comprises a photodiode (31), an operational amplifier (32), a data storage medium (33) and a computer (34); the photodiode (31) is arranged at a rear light outlet of the laser (11) and is connected with the operational amplifier (32); the operational amplifier (32) is connected with the data storage medium (33); the data storage medium (33) is connected to the computer (34).
3. The liquid trace detection device according to claim 1, wherein the laser (11) is a gaussian beam laser.
4. The liquid trace detection device according to claim 1, wherein, in use, the micro-displacement stage (22) is continuously sinusoidally vibrated according to the generated sinusoidal signal of the signal generator (21).
5. The liquid trace detection device according to claim 1, wherein the following condition is satisfied:
b2>>L2；
b2>>d2；
L>l；
wherein b is a confocal parameter of the laser (11), L is a distance from the laser (11) to the plane mirror (14), d is a distance from the laser (11) to a sample to be detected, and L is a length of the sample.
6. The liquid trace detection device according to claim 1, wherein the photoelectric signal acquisition, conversion and processing module (3) extracts the envelope amplitude of the photo-thermal self-mixing signal by a maximum detection algorithm during signal processing.
7. The liquid trace detection device according to claim 1, wherein the photoelectric signal acquisition, conversion and processing module (3) obtains the photo-thermal self-mixing parameter s (m) of the sample to be detected according to the following formula during the signal processing:
wherein, | Δ PF0I is the envelope amplitude of the initial moment of the Mth laser heating period; | Δ PFt(at tt1)And | is the envelope amplitude at the moment when the mth laser heating period t is t 1.
8. The liquid trace detection device according to claim 1, wherein the photoelectric signal acquisition, conversion and processing module (3) obtains the solution concentration C of the sample to be detected according to the following formula during the signal processing:
wherein S (M) represents a photothermal self-mixing parameter; k1、K2And K3Are all preset constants; dn/dT is the coefficient of change of the refractive index of the sample to be detected along with the temperature; p is the output optical power of the laser (11); l is the length of the sample; the Joule coefficient J is 4.18; k is the thermal conductivity of the sample to be detected; omega0The beam radius of the laser generated by the laser (11) at the light outlet of the laser (11); t is t1Is the excitation time length; t is tcThe photothermal time constant.
9. The liquid trace detection device according to claim 8, wherein the constant K is3Set by the following formula:
wherein alpha is0The absorption coefficient of the sample to be detected at a solution concentration of 0 is shown.
10. A liquid trace amount detection method implemented based on the liquid trace amount detection apparatus according to claims 1 to 9, characterized by comprising the steps of:
s1, placing the cuvette containing the sample to be detected in the sample groove (13), and starting the laser (11) and the optical switch (12) to irradiate the sample to be detected for a period of time;
s2, collecting photo-thermal self-mixing signals, and extracting the photo-thermal self-mixing signals of the heating section after normalization processing;
and S3, extracting the envelope amplitude of the photo-thermal self-mixing signal to obtain photo-thermal self-mixing parameters of the sample to be detected, and measuring the solution concentration of the sample to be detected according to the photo-thermal self-mixing parameters.
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