Quartz enhanced photo-thermal spectrum concentration data acquisition method, light intensity correction method and device

Abstract

The invention provides a quartz enhanced photo-thermal spectral concentration data acquisition method and a light intensity correction method and device, and the light intensity correction method comprises the following steps: selecting data of non-absorption positions at two sides of an original 2f signal as base lines, and adjusting the value range of the base lines at the two sides according to an actually measured spectral signal; fourth-order polynomial fitting is carried out according to the base line, and a light intensity nonlinear response background signal in the whole spectral range is obtained through fitting; a background obtained by fourth-order polynomial fitting is deducted from the measured harmonic signal, and the peak-to-peak value of the signal is in direct proportion to the light intensity and the concentration of the gas to be measured; and dividing the peak-to-peak value of the 2f signal from which the background is deducted by the amplitude of the background signal to obtain a normalized peak-to-peak value of the 2f signal. According to the invention, light intensity correction of quartz enhanced photo-thermal spectrum concentration data is realized, light intensity jittering and drifting are prevented from introducing errors to system measurement, light noise can be inhibited, and the long-term stability of the system can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of quartz tuning fork enhanced photoacoustic spectroscopy, and particularly relates to a method for collecting concentration data of quartz enhanced photoacoustic spectroscopy, a method for correcting light intensity, and a device therefor. Background Art

[0002] Quartz tuning fork enhanced photoacoustic spectroscopy has the advantages of high sensitivity, strong anti-interference ability, small volume, etc., and is widely used in many fields such as environmental detection, industrial control, and medical diagnosis. This technology couples a laser beam to the surface of a quartz tuning fork, uses the quartz tuning fork as a photoacoustic signal sensor, and combines phase-locked detection to achieve ultra-high sensitivity detection. The frequency response bandwidth of the quartz tuning fork is relatively narrow, usually within a few Hz. Therefore, a single tuning fork can only measure a single frequency harmonic signal. Combining with the currently commonly used second harmonic measurement, only the concentration measurement can be achieved, and the synchronous inversion of the light intensity cannot be achieved. Summary of the Invention

[0003] Object of the Invention: To propose a method for collecting concentration data of quartz enhanced photoacoustic spectroscopy, a method for correcting light intensity, and a device therefor, so as to solve the above problems existing in the prior art.

[0004] In a first aspect, a method for collecting concentration data of quartz enhanced photoacoustic spectroscopy is proposed, and the steps are as follows:

[0005] Use a microcontroller to set the frequency control word and initial phase of a frequency synthesizer, so that the frequency synthesizer outputs a sawtooth sweep signal and superimposes a high-frequency modulation signal;

[0006] Input the sawtooth sweep signal and the high-frequency modulation signal into a laser, and emit a first laser beam from the laser; the frequency of the high-frequency modulation signal is half of the center resonance frequency of the quartz tuning fork;

[0007] Couple the first laser beam to an optical fiber amplifier, and amplify the light intensity of the first laser beam and the amplitude of its non-linear response term by the optical fiber amplifier to form a second laser beam;

[0008] Adjust the second laser beam to pass through a gas measurement cell and converge on the surface of the quartz tuning fork to excite a photoacoustic signal;

[0009] Input the photoacoustic signal into a signal conditioning circuit, and amplify and filter the photoacoustic signal by the signal conditioning circuit and then demodulate it by a lock-in amplifier to obtain a harmonic signal;

[0010] Input the harmonic signal into an analog-to-digital converter to obtain harmonic signal data, and the harmonic signal data is the concentration data of the photoacoustic spectroscopy.

[0011] In a second aspect, a device for collecting concentration data of quartz enhanced photoacoustic spectroscopy is proposed, and the device includes:

[0012] A microcontroller; the microcontroller is used to set the frequency control word and the initial phase of a frequency synthesizer, so that the frequency synthesizer outputs a sawtooth scanning signal and superimposes a high-frequency modulation signal;

[0013] A laser, electrically connected to the microcontroller; the laser is used to receive the sawtooth scanning signal and the high-frequency modulation signal, and output a first laser beam; the frequency of the high-frequency modulation signal is half of the center resonance frequency of a quartz tuning fork;

[0014] An optical fiber amplifier, electrically connected to the laser; the first laser beam is coupled to the optical fiber amplifier, and the optical fiber amplifier amplifies the light intensity of the first laser beam and the amplitude of its non-linear response term to form a second laser beam;

[0015] A gas measurement cell, arranged behind the optical fiber amplifier and within the output range of the optical fiber amplifier; adjusting the second laser beam to converge on the surface of the quartz tuning fork after passing through the gas measurement cell to excite a photo-thermal signal;

[0016] A conditioning circuit; the conditioning circuit is used to receive the photo-thermal signal, and the signal conditioning circuit amplifies and filters the photo-thermal signal and then demodulates it by a lock-in amplifier to obtain a harmonic signal;

[0017] An analog-to-digital converter, electrically connected to the conditioning circuit; the analog-to-digital converter inputs the harmonic signal into the analog-to-digital converter to obtain harmonic signal data, and the harmonic signal data is the photo-thermal spectroscopy concentration data.

[0018] In a third aspect, a method for correcting the light intensity of photo-thermal spectroscopy concentration data applied to quartz-enhanced photo-thermal spectroscopy is proposed, including the following steps:

[0019] Select data at positions without absorption on both sides of the original 2f signal as the baseline, and the value range of the two-side baseline is adjusted according to the actually measured spectral signal;

[0020] Perform a fourth-order polynomial fitting based on the selected baseline, and fit to obtain the light intensity non-linear response background signal within the entire spectral range. The amplitude of the signal is only proportional to the light intensity and has nothing to do with the concentration of the gas to be measured;

[0021] Among them, the expression of the fourth-order polynomial fitting is as follows:

[0022] S 2f_base =ax 4 +bx 3 +cx 2 +dx+e;

[0023] In the formula, S 2f_baseIt represents the background signal of the nonlinear response of light intensity in the entire spectral range obtained by fitting. x represents the sampling point, and a, b, c, d, and e are the parameters obtained by fitting.

[0024] The measured harmonic signal is subtracted by the background obtained by fourth-order polynomial fitting. The peak-to-peak value of this signal is proportional to the light intensity and is also proportional to the concentration of the gas to be measured.

[0025] The peak-to-peak value of the 2f signal after background subtraction is divided by the amplitude of the background signal to obtain the normalized peak-to-peak value of the 2f signal, thus completing the light intensity correction of the concentration data of the quartz-enhanced photoacoustic spectroscopy.

[0026] In the fourth aspect, a device for light intensity correction of concentration data of quartz-enhanced photoacoustic spectroscopy is proposed. The device includes:

[0027] A baseline selection unit for selecting the data at the positions without absorption on both sides of the original 2f signal as the baseline, and the value range of the two-side baselines is adjusted according to the actually measured spectral signal.

[0028] A first calculation unit for performing fourth-order polynomial fitting based on the selected baseline to obtain the background signal of the nonlinear response of light intensity in the entire spectral range. The amplitude of the signal is only proportional to the light intensity and has nothing to do with the concentration of the gas to be measured.

[0029] A second calculation unit for subtracting the background obtained by fourth-order polynomial fitting from the measured harmonic signal. The peak-to-peak value of this signal is proportional to the light intensity and is also proportional to the concentration of the gas to be measured.

[0030] An output unit for dividing the peak-to-peak value of the 2f signal after background subtraction by the amplitude of the background signal to obtain the normalized peak-to-peak value of the 2f signal, thus completing the light intensity correction of the photoacoustic spectroscopy concentration data.

[0031] In the fifth aspect, a computer-readable storage medium is proposed. At least one executable instruction is stored in the storage medium. When the executable instruction runs on an electronic device, the electronic device is made to execute the method for collecting concentration data of quartz-enhanced photoacoustic spectroscopy as described in the first aspect, or execute the light intensity correction method as described in the third aspect.

[0032] The present invention has the following beneficial effects: The method for collecting concentration data of quartz-enhanced photoacoustic spectroscopy and the light intensity correction method proposed by the present invention can achieve accurate light intensity correction of the concentration data of quartz-enhanced photoacoustic spectroscopy, avoid errors introduced by light intensity jitter and drift to the system measurement, help suppress light noise and improve the long-term stability of the system. Description of the Drawings

[0033] Figure 1 It is a schematic structural diagram of the device for collecting concentration data of quartz-enhanced photoacoustic spectroscopy in an embodiment of the present invention.

[0034] Figure 2 It is a comparison chart between the original harmonic signal and the polynomial fitting curve.

[0035] Figure 3 It is a schematic diagram of the 2f signal after background subtraction.

[0036] Figure 4 It is a flowchart of the light intensity correction method applied to the concentration data of quartz-enhanced photoacoustic spectroscopy.

[0037] Figure 5 It is a flowchart of the method for collecting concentration data of quartz-enhanced photoacoustic spectroscopy in the embodiment of the present invention.

[0038] The reference numerals in the figure are: microcontroller 1, frequency synthesizer 2, laser and driver 3, fiber amplifier 4, gas measurement cell 5, quartz tuning fork 6, signal conditioning circuit 7, lock-in amplifier 8, analog-to-digital converter 9. Specific Embodiments

[0039] In the following description, a large number of specific details are given to provide a more thorough understanding of the present invention. However, it is obvious to those skilled in the art that the present invention can be implemented without one or more of these details. In other examples, in order to avoid confusion with the present invention, some technical features well known in the art are not described.

[0040] Embodiment 1:

[0041] This embodiment discloses a device for collecting concentration data of quartz-enhanced photoacoustic spectroscopy. The system hardware part is as Figure 1 shown, including a microcontroller 1, a frequency synthesizer 2, a laser and driver 3, a fiber amplifier 4, a gas measurement cell 5, a quartz tuning fork 6, a signal conditioning circuit 7, a lock-in amplifier 8, and an analog-to-digital converter 9. The microcontroller 1 sets the frequency control word and the initial phase of the frequency synthesizer 2 to output a sawtooth scanning signal and superimpose a high-frequency modulation signal, and inputs this signal to the laser and driver 3. The frequency of the high-frequency modulation signal is half of the center resonance frequency of the quartz tuning fork. The laser beam is coupled to the fiber amplifier 4 to amplify the laser light intensity and the amplitude of its non-linear response term, and then the beam is adjusted to pass through the gas measurement cell 5 and converge on the surface of the quartz tuning fork 6 to excite a photoacoustic signal. The signal conditioning circuit 7 amplifies and filters the output signal of the quartz tuning fork and demodulates it by the lock-in amplifier 8 to obtain a harmonic signal, which is finally input to the analog-to-digital converter 9 to realize the data acquisition of the harmonic signal.

[0042] Using the microcontroller 1, control the frequency synthesizer 2 and the laser driver system to output a modulated current signal to drive the laser, where the modulation frequency is half of the central resonance frequency of the quartz tuning fork 6. Use the fiber amplifier 4 to amplify the laser output power and enhance the amplitude of the laser intensity nonlinear response term. After the light beam passes through the measurement cell filled with the gas to be measured, it is focused on the surface of the tuning fork to excite the quartz-enhanced photo-thermal signal. At this time, the excited photo-thermal signal not only contains the second harmonic signal (2f), but also contains the background signal excited due to the nonlinear response of the light intensity. The lock-in amplifier 8 can be used to demodulate and obtain Figure 2 the original harmonic signal S shown by the black solid line in 2f_raw .

[0043] Embodiment 2:

[0044] Based on the foregoing Embodiment 1, this embodiment discloses a method for collecting quartz-enhanced photo-thermal spectroscopy concentration data. The specific steps are as follows:

[0045] S101. Use the microcontroller 1 to set the frequency control word and the initial phase of the frequency synthesizer 2, so that the frequency synthesizer 2 outputs a sawtooth scanning signal and superimposes a high-frequency modulation signal.

[0046] S102. Input the sawtooth scanning signal and the high-frequency modulation signal into the laser and driver 3, and the laser and driver 3 emits a first laser beam; the frequency of the high-frequency modulation signal is half of the central resonance frequency of the quartz tuning fork 6.

[0047] S103. The first laser beam is coupled to the fiber amplifier 4, and the fiber amplifier 4 amplifies the light intensity of the first laser beam and the amplitude of its nonlinear response term to form a second laser beam.

[0048] S104. Adjust the second laser beam to pass through the gas measurement cell 5 and then converge on the surface of the quartz tuning fork 6 to excite a photo-thermal signal.

[0049] S105. Input the photo-thermal signal into the signal conditioning circuit 7, and the signal conditioning circuit 7 amplifies and filters the photo-thermal signal and then demodulates it by the lock-in amplifier 8 to obtain a harmonic signal.

[0050] S106. Input the harmonic signal into the analog-to-digital converter 9 to obtain the original harmonic signal data, and the original harmonic signal data is the original photo-thermal spectroscopy harmonic signal data.

[0051] Embodiment 3:

[0052] For the original photo-thermal spectroscopy harmonic signal data collected through the above Embodiment 1 or Embodiment 2, this embodiment discloses the specific processing flow of the original photo-thermal spectroscopy harmonic signal data, as Figure 4 shown:

[0053] First, take Figure 2 the data within the gray rectangles on both sides of the black solid line in

[0054] as the baseline. The spectral data corresponding to this part of the baseline does not contain gas absorption information. The value ranges of the two-sided baselines are adjusted according to the actually measured spectral signals; Figure 2 the background signal S shown by the black dashed line in 2f_base , and the amplitude of this signal is only proportional to the light intensity and has nothing to do with the concentration of the gas to be measured;

[0055] Then, use the data selected in the previous step as the baseline and perform a fourth-order polynomial fitting to obtain the background signal within the entire measured harmonic signal range, that is, 2f_raw Subtract the background signal S obtained by the fourth-order polynomial fitting from the measured original harmonic signal S 2f_base , and then the Figure 3 background-subtracted 2f signal (S 2f_raw -S 2f_base ) shown in can be obtained. The peak-to-peak value of this signal is proportional to the light intensity and is also proportional to the concentration of the gas to be measured;

[0056] Finally, divide the peak-to-peak value of the background-subtracted 2f signal (S 2f_raw -S 2f_base ) by the amplitude of the background signal (S 2f_base ) to obtain the peak-to-peak value of the normalized 2f signal. This value is only proportional to the concentration of the gas to be measured and has nothing to do with the light intensity, thus realizing the light intensity correction of the concentration data of the quartz-enhanced photoacoustic spectroscopy.

[0057] As described above, although the present invention has been shown and described with reference to specific preferred embodiments, it should not be construed as a limitation of the present invention itself. Various changes in form and detail may be made without departing from the spirit and scope of the present invention defined by the appended claims.

Claims

1. A method for collecting quartz-enhanced photo-thermal spectroscopy concentration data, characterized in that, It includes the following steps: S101. Use a microcontroller to set the frequency control word and initial phase of a frequency synthesizer, so that the frequency synthesizer outputs a sawtooth scanning signal and superimposes a high-frequency modulation signal; S102. Input the sawtooth scanning signal and the high-frequency modulation signal into a laser, and emit a first laser beam from the laser; the frequency of the high-frequency modulation signal is half of the center resonance frequency of a quartz tuning fork; S103. Couple the first laser beam to an optical fiber amplifier, and amplify the light intensity of the first laser beam and the amplitude of its non-linear response term by the optical fiber amplifier to form a second laser beam; S104. Adjust the second laser beam to converge on the surface of the quartz tuning fork after passing through a gas measurement cell, thereby exciting a photo-thermal signal; S105. Input the photo-thermal signal into a signal conditioning circuit, and amplify and filter the photo-thermal signal by the signal conditioning circuit, and then demodulate it by a lock-in amplifier to obtain a harmonic signal; S106. Input the harmonic signal into an analog-to-digital converter to obtain original harmonic signal data, and the original harmonic signal data is the original photo-thermal spectral harmonic signal data.

2. A method for correcting the light intensity of quartz-enhanced photo-thermal spectroscopy concentration data, characterized in that It includes the following steps: S201. Use the quartz-enhanced photo-thermal spectroscopy concentration data acquisition method as described in claim 1 to collect the original harmonic signal data S 2f_raw ; S202. Select the data of the original harmonic signal S 2f_raw The data at the positions without absorption on both sides are used as the baseline, and the value range of the baselines on both sides is adjusted according to the actually measured spectral signals; S203. Perform a fourth-order polynomial fitting based on the baseline described in step S202 to obtain the background signal S of the light intensity non-linear response over the entire spectral range. 2f_base , where the background signal S of the light intensity non-linear response 2f_base has an amplitude that is only proportional to the light intensity and independent of the concentration of the gas to be measured. S204. Subtract the background signal S of the non-linear response of the light intensity from the original harmonic signal data S 2f_raw to obtain the 2f signal after background subtraction. The peak-to-peak value of the 2f signal after background subtraction is proportional to the light intensity and is also proportional to the concentration of the gas to be measured; 2f_base ​ S205. Divide the peak-to-peak value of the 2f signal after background subtraction by the amplitude of the optical intensity non-linear response background signal S 2f_base to obtain the normalized peak-to-peak value of the 2f signal, and complete the optical intensity correction of the concentration data of the quartz-enhanced photo-thermal spectroscopy.

3. The light intensity correction method according to claim 2, characterized in that The expression of the fourth-order polynomial fitting in step S203 is as follows: S 2f_base = ax 4 + bx 3 + cx 2 + dx + e; where S 2f_base represents the background signal of the non-linear response of the light intensity in the entire spectral range obtained by fitting, x represents the sampling point, and a, b, c, d, and e are the parameters obtained by fitting.

4. A quartz-enhanced photo-thermal spectroscopy concentration data acquisition device, characterized in that, It includes: A microcontroller, which is used to set the frequency control word and initial phase of a frequency synthesizer, so that the frequency synthesizer outputs a sawtooth scanning signal and superimposes a high-frequency modulation signal; A laser, electrically connected to the microcontroller; the laser is used to receive the sawtooth scanning signal and the high-frequency modulation signal, and output a first laser beam; the frequency of the high-frequency modulation signal is half of the center resonance frequency of a quartz tuning fork; An optical fiber amplifier, electrically connected to the laser; the first laser beam is coupled to the optical fiber amplifier, and the optical fiber amplifier amplifies the light intensity of the first laser beam and the amplitude of its non-linear response term to form a second laser beam; A gas measurement cell, arranged behind the optical fiber amplifier and within the output range of the optical fiber amplifier; adjust the second laser beam to converge on the surface of the quartz tuning fork after passing through the gas measurement cell, thereby exciting a photo-thermal signal; A conditioning circuit, which is used to receive the photo-thermal signal, amplify and filter the photo-thermal signal by the signal conditioning circuit, and then demodulate it by a lock-in amplifier to obtain a harmonic signal; An analog-to-digital converter, electrically connected to the conditioning circuit; the analog-to-digital converter inputs the harmonic signal into the analog-to-digital converter to obtain original harmonic signal data, and the original harmonic signal data is the original photo-thermal spectral harmonic signal data.

5. An optical intensity correction device applied to the concentration data of quartz-enhanced photo-thermal spectroscopy, characterized in that, It includes: A baseline selection unit, which is used to select the original harmonic signal data S 2f_raw The data at the positions without absorption on both sides are used as the baseline, and the value range of the baselines on both sides is adjusted according to the actually measured spectral signal; A first calculation unit, configured to perform a fourth-order polynomial fitting based on the baseline, and obtain a light intensity non-linear response background signal S within the entire spectral range through fitting 2f_base ; A second calculation unit for subtracting the optical intensity non-linear response background signal S from the original harmonic signal data S 2f_raw to obtain a 2f signal with the background subtracted; 2f_base ​ An output unit for dividing the peak-to-peak value of the 2f signal after background subtraction by the amplitude of the optical intensity non-linear response background signal S 2f_base to obtain the peak-to-peak value of the normalized 2f signal, thereby completing the optical intensity correction of the concentration data of the quartz-enhanced photo-thermal spectroscopy.

6. A computer-readable storage medium, characterized in that, At least one executable instruction is stored in the storage medium. When the executable instruction runs on an electronic device, it enables the electronic device to execute the method for correcting the light intensity of the photo-thermal spectral concentration data applied to the quartz-enhanced photo-thermal spectroscopy as claimed in claim 2.

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