Method and storage medium for subtracting stray light for broadband cavity enhanced absorption spectrum

Abstract

A method and storage medium for subtracting stray light in broadband cavity enhanced absorption spectroscopy according to the present invention. The steps of the method are as follows: S1. Measure without using a filter in the broadband cavity enhanced absorption spectroscopy system to obtain a spectrum I(λ); S2. Select a suitable filter according to the main wavelength band of the interfering light to obtain an uncorrected stray light spectrum I0(λ); S3. Correct the data of I0(λ) to obtain the corrected I0′(λ), which is the part of the stray light caused by the interfering light in the measurement wavelength band; S4. During the measurement process of the broadband cavity enhanced absorption spectroscopy system, a filter may not be used, and only the obtained spectra need to be corrected for stray light. After using the present invention, a filter may not be used during the actual measurement process of the broadband cavity enhanced absorption spectroscopy system, avoiding the situation that using a filter will reduce the radiation intensity of the "true" spectrum and that the filter may have a certain structure and interfere with the fitting result of the absorption spectrum, thereby improving the system performance.

Description

Technical Field

[0001] The invention relates to the technical field of atmospheric trace gas detection, and in particular to a method and a storage medium for subtracting stray light from a broadband cavity enhanced absorption spectrum. Background Art

[0002] In view of the atmospheric pollution problem in the process of rapid economic development in my country, it is necessary to develop a variety of key technologies for atmospheric composite pollution monitoring, mainly advanced environmental monitoring technologies, to improve the detection sensitivity and the types of trace gases detected, and to detect low-dose and difficult-to-detect pollutants in the environment with higher sensitivity. Broadband cavity-enhanced absorption spectroscopy technology is one of the most advanced trace gas detection technologies in the world. This technology achieves qualitative and quantitative measurement by measuring the "fingerprint" characteristic absorption of light radiation by trace gas components, and combines the resonant cavity principle. Photons can be reflected back and forth in the optical cavity to increase the optical path. An optical cavity of less than 1m can achieve an effective optical path of several kilometers or even more than ten kilometers, which greatly improves the system performance. The detection sensitivity can reach ppt (10 -12 ) level, and has the advantages of high sensitivity, high precision, high stability, high time resolution, real-time online in-situ detection, and no chemical interference. After more than ten years of development, broadband cavity-enhanced absorption spectroscopy technology has been successfully used for high-sensitivity measurement of a variety of atmospheric trace gases, such as NO2, NO3, N2O5, I2, IO, HONO, CHOCHO, etc.

[0003] The core component of the broadband cavity enhanced absorption spectroscopy system is an optical resonant cavity with high-reflection mirrors (the reflectivity of the lens is usually greater than 0.9995) at both ends. The light reflects back and forth in the optical resonant cavity, which can greatly increase the optical path. However, due to the limitations of existing coating technology, the high-reflection area of ​​the high-reflection mirror is usually only tens of nanometers. Therefore, the measurement band range of the broadband cavity enhanced absorption spectroscopy system corresponds to tens of nanometers. At present, LEDs are mainly used as light sources in broadband cavity enhanced absorption spectroscopy systems. Under normal circumstances, the spectral range of the main radiation band of LEDs is about tens of nanometers, which matches the high-reflection area of ​​the high-reflection mirrors in the broadband cavity enhanced absorption spectroscopy system. However, due to problems such as LED manufacturing technology, the chip often contains trace amounts of "impurities", resulting in a small amount of light radiation from the LED light source outside the main band. The main radiation band of the LED light source selected by the broadband cavity enhanced absorption spectroscopy technology is basically consistent with the high-reflection area of ​​the high-reflection mirror. Since the reflectivity of the lens of the high-reflection mirror in the high-reflection area is extremely high (the reflectivity of the high-reflection mirror lens used in the broadband cavity enhanced absorption spectroscopy system is usually greater than 0.9995), the transmittance of the lens corresponding to the high-reflection area of ​​the high-reflection mirror is extremely low, resulting in the light radiation emitted by the LED light source passing through the resonant cavity formed by the high-reflection mirror. The light radiation in the high-reflection area of ​​the high-reflection mirror will be greatly reduced, and a small part of the light radiation of the LED outside the high-reflection area of ​​the high-reflection mirror will directly pass through the high-reflection mirror, which will lead to relatively strong interference light. This interference light will cause a certain amount of stray light in the measurement band. If the stray light is not processed, it will affect the measurement accuracy of the cavity enhanced absorption spectroscopy system.

[0004] Therefore, in the measurement process of broadband cavity enhanced absorption spectroscopy technology, it is usually necessary to match appropriate filters to filter out the interference light outside the high-reflection area, thereby eliminating the stray light in the measurement band and avoiding the influence of stray light on the measurement accuracy of the broadband cavity enhanced absorption spectroscopy system. However, although the use of filters can eliminate stray light, it will inevitably reduce the radiation intensity of the absorption spectrum in the measurement band, thereby reducing the system signal-to-noise ratio to a certain extent; on the one hand, the measurement spectrum obtained after using the filter will be superimposed with the transmittance curve of the filter in the measurement band, and the transmission structure of the filter may have a certain impact on the absorption spectrum fitting. Summary of the invention

[0005] The present invention provides a method for subtracting stray light from broadband cavity enhanced absorption spectrum, which can solve at least one of the above technical problems.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for subtracting stray light from broadband cavity enhanced absorption spectrum comprises the following steps:

[0008] S1. In the broadband cavity enhanced absorption spectroscopy system, the spectrum I(λ) is obtained without using a filter, and the main band (λ3-λ4) of interfering light that causes stray light in the measurement band (λ1-λ2) is determined based on the peak shape of the spectrum I(λ);

[0009] S2. According to the main wavelength band of the interference light (λ3-λ4), a suitable filter is selected, which has extremely low transmittance in the measurement wavelength band (λ1-λ2) and high transmittance in the main wavelength band of the interference light (λ3-λ4), to obtain the uncorrected stray light spectrum I0(λ);

[0010] S3, select a band (λ5-λ6) outside the measurement band and without interference light, fit the spectrum I(λ5-λ6) with I0(λ5-λ6) to obtain a fitting function, use the fitting function to correct the data of I0(λ), and obtain the corrected I0′(λ), which is the stray light part caused by the interference light to the measurement band;

[0011] S4. During the use of the broadband cavity enhanced absorption spectroscopy system, it is not necessary to use a filter. The obtained spectra are corrected to obtain the spectrum I′(λ) after deducting the stray light, that is, I′(λ)=I(λ)-I0′(λ), so that the influence of stray light in the measurement of broadband cavity enhanced absorption spectroscopy technology can be deducted.

[0012] Among them, the stray light in the broadband cavity enhanced absorption spectroscopy technology refers to the light radiation outside the measurement band of the broadband cavity enhanced absorption spectroscopy technology (high reflection area of ​​the high reflection mirror) will directly pass through the high reflection mirror. If the intensity of the interfering light is higher than the intensity of the measurement band, it will cause a certain degree of stray light in the measurement band, thereby causing a certain impact on the measurement accuracy.

[0013] On the other hand, the present invention further discloses a computer-readable storage medium storing a computer program, wherein when the computer program is executed by a processor, the processor executes the steps of the above method.

[0014] It can be seen from the above technical solution that the method for subtracting stray light from broadband cavity enhanced absorption spectrum of the present invention divides the measurement spectrum of the broadband cavity enhanced absorption spectrum system into a "real" spectrum and a "false" spectrum caused by stray light, and subtracts the stray light in the measurement band caused by the interference light by differential means to obtain the "real" spectrum of the measurement band. In this way, in the actual measurement process of the broadband cavity enhanced absorption spectrum system, the atmospheric components can be accurately measured without using filters, avoiding the situation that the use of filters will reduce the radiation intensity of the "real" spectrum, and the use of filters may have certain structures and interfere with the absorption spectrum fitting results, which can further improve the performance of the broadband cavity enhanced absorption spectrum system. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a flow chart of a method for subtracting stray light using broadband cavity enhanced absorption spectroscopy technology in an embodiment of the present invention;

[0016] Figure 2 The black line is a typical spectrum of a 365nm broadband cavity enhanced absorption spectroscopy system (without using a filter), and the gray dotted line is the spectrum after using a long-wave pass cutoff filter.

[0017] Figure 3 The upper figure is a comparison between the reflectivity of the lens of the broadband cavity enhanced absorption spectroscopy system calibrated by the Rayleigh scattering difference method of different gases when the stray light is not considered and the reflectivity of the real lens; the lower figure is a comparison between the reflectivity of the lens of the broadband cavity enhanced absorption spectroscopy system calibrated by the Rayleigh scattering difference method of different gases after the stray light correction is performed using the present invention and the reflectivity of the real lens. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0019] like Figure 1 As shown, the method for subtracting stray light from broadband cavity enhanced absorption spectrum described in this embodiment includes the following steps:

[0020] S1. In the broadband cavity enhanced absorption spectroscopy system, the measurement is performed without using a filter to obtain the spectrum I(λ), and the main band (λ3-λ4) of interfering light that causes stray light in the measurement band (λ1-λ2) is determined based on the peak shape of the spectrum I(λ).

[0021] S2. According to the main wavelength band of the interference light (λ3~λ4), a suitable filter is selected, which has extremely low transmittance in the measurement band (λ1~λ2) and high transmittance in the main wavelength band of the interference light (λ3~λ4), to obtain the uncorrected stray light spectrum I0(λ).

[0022] S3. Select a band (λ5-λ6) outside the measurement band and without interference light, fit the spectrum I(λ5-λ6) with I0(λ5-λ6) to obtain a fitting function, use the fitting function to correct the data of I0(λ), and obtain the corrected I0′(λ), which is the stray light part caused by the interference light to the measurement band.

[0023] S4. During the use of the broadband cavity enhanced absorption spectroscopy system, it is not necessary to use a filter. The obtained spectra are corrected to obtain the spectrum I′(λ) after deducting the stray light, that is, I′(λ)=I(λ)-I0′(λ), so that the influence of stray light in the measurement of broadband cavity enhanced absorption spectroscopy technology can be deducted.

[0024] Among them, light radiation outside the measurement band of broadband cavity enhanced absorption spectroscopy technology (high reflection area of ​​high reflection mirror) will directly pass through the high reflection mirror. If the intensity of the interfering light is higher than the intensity of the measurement band, it will cause a certain degree of stray light in the measurement band, thereby causing a certain impact on the measurement accuracy.

[0025] The following are examples:

[0026] Taking the 365nm broadband cavity enhanced absorption spectroscopy system as an example for detailed explanation, the 365nm broadband cavity enhanced absorption spectroscopy system usually uses an LED with a central wavelength of 365nm as the light source. The full width at half maximum of the LED is about 13nm, and the typical high-reflection mirror used has a nominal reflectivity greater than 99.95% in the 360-390nm band. It is known that the central wavelength of the LED light source used is 365nm, and the high-reflection area of ​​the high-reflection mirror is 360nm-390nm, so the actual measurement band is 360nm-390nm. According to Figure 1 The method for subtracting stray light using broadband cavity enhanced absorption spectroscopy is shown in the figure. The specific process is as follows: 1. The 365nm broadband cavity enhanced absorption spectroscopy system is measured without using a filter to obtain the spectrum I(λ), that is, Figure 2 Black line, according to Figure 2 The black line shows that the spectrum intensity greater than 415nm in the spectrum is extremely strong, causing the spectrometer to be saturated. Therefore, the main band of interfering light (>415nm) that causes stray light in the measurement band (360nm~390nm) is determined. 2. According to the main band of interfering light (>415nm), a 400nm long-wave pass cutoff filter (FELH0400, high-quality long-wave pass filter, cutoff wavelength: 400nm, Thorlabs) is selected. The transmittance of this filter in the measurement band (360nm~390nm) is extremely low and the transmittance in the main band of interfering light (>415nm) is relatively high. The uncorrected stray light spectrum I0(λ) is obtained. Figure 2Gray dotted line. 3. Since the transmittance of the selected filter in the main band of interference light cannot reach 100%, the light radiation intensity of the interference light will inevitably be weakened to a certain extent, so the stray light spectrum I0(λ) needs to be corrected. Select a spectral band (305nm~320nm) outside the measurement band and without interference light, fit the spectrum I(305nm~320nm) with I0(305nm~320nm), obtain the fitting function, use the fitting function to correct the data of I0(λ), and obtain the corrected i0′(λ). I0′(360nm~390nm) is the stray light part caused by the interference light to the measurement band. 4. During the use of the broadband cavity enhanced absorption spectroscopy system, the filter can be used without using the filter. The obtained spectra are corrected to obtain the spectrum I′(λ) after deducting the stray light, that is, I′(λ)=I(λ)-I0′(λ), then the influence of stray light in the measurement of broadband cavity enhanced absorption spectroscopy technology can be deducted.

[0027] In order to verify the effectiveness of the method proposed in the present invention for subtracting stray light using broadband cavity enhanced absorption spectroscopy, the method proposed by Washenfelder et al. (Washenfelder RA, Langford AO, Fuchs H, Brown SS 2008 Atmos. Chem. Phys. 8 7779) for calibrating the reflectivity of a lens using the Rayleigh scattering difference of different gas molecules is adopted, and the data expression is as follows:

[0028]

[0029] in, is the Rayleigh scattering coefficient of high-purity nitrogen, is the Rayleigh scattering coefficient of high-purity helium, and I He (λ) are the measured spectra of the broadband cavity enhanced absorption spectroscopy system when the cavity is filled with high-purity nitrogen and helium, R(λ) is the curve of the change of lens reflectivity with wavelength, and d is the cavity length.

[0030] like Figure 3 As shown in (a), the gray dot line is the 365nm broadband cavity enhanced absorption spectroscopy system in the actual measurement process without using filters and without stray light correction, that is, the measured spectrum contains stray light, and the reflectivity of the high-reflectivity mirror lens calibrated by the difference of Rayleigh scattering of different gas molecules is obviously different from the reflectivity of the high-reflectivity mirror lens of the 365nm broadband cavity enhanced absorption spectroscopy system, indicating that if the broadband cavity enhanced absorption spectroscopy system does not use filters during the measurement process, its measured spectrum will be affected by stray light, and the spectral data obtained using this measured spectrum will have certain errors.

[0031] like Figure 3As shown in (b), the gray dot line is the actual measurement process of the 365nm broadband cavity enhanced absorption spectroscopy system without using a filter, but using the method of subtracting stray light proposed in the present invention to correct the stray light of the measured spectrum. Then, the reflectivity of the high-reflective mirror lens calibrated by the difference of Rayleigh scattering of different gas molecules can be seen. It can be seen that the reflectivity of the high-reflective mirror lens calibrated using the data after subtracting stray light is consistent with the reflectivity of the real high-reflective mirror lens, indicating that the method of subtracting stray light for broadband cavity enhanced absorption spectroscopy technology proposed by the present invention is effective and accurate, and can achieve the measurement process of the broadband cavity enhanced absorption spectroscopy system without using a filter, and can also effectively eliminate the influence of stray light.

[0032] In yet another aspect, the present invention further discloses a computer-readable storage medium storing a computer program, wherein when the computer program is executed by a processor, the processor executes the steps of any of the above methods.

[0033] On the other hand, the present invention further discloses a computer device, including a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor executes the steps of any of the above methods.

[0034] In another embodiment provided by the present application, a computer program product including instructions is also provided, which, when executed on a computer, enables the computer to execute the steps of any method in the above embodiments.

[0035] It is understandable that the system provided by the embodiment of the present invention corresponds to the method provided by the embodiment of the present invention, and the explanation, examples and beneficial effects of the relevant contents can refer to the corresponding parts in the above method.

[0036] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program, and the program can be stored in a non-volatile computer-readable storage medium. When the program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to memory, storage, database or other media used in the embodiments provided in this application can include non-volatile and / or volatile memory. Non-volatile memory may include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM) or flash memory. Volatile memory may include random access memory (RAM) or external cache memory. As an illustration and not limitation, RAM is available in many forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link (Synchlink) DRAM (SLDRAM), memory bus (Rambus) direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM).

[0037] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for subtracting stray light from broadband cavity enhanced absorption spectroscopy, characterized in that: The following steps are included: S1. Measurement without using filters in broadband cavity enhanced absorption spectroscopy system to obtain spectrum , and according to the spectrum The peak shape determination results in the measurement band Main wavelength band of interfering light with stray light ; S2. According to the main band of interference light , select the corresponding filter, which is in the measurement band The transmittance is extremely low to the set value and in the main band of interference light The transmittance is high, and the uncorrected stray light spectrum is obtained ; S3. Select a band outside the measurement band with no interfering light , the spectrum and Do the fitting, get the fitting function, and use the fitting function to Correct the data and obtain the corrected , which is the stray light part caused by the interference light to the measurement band; S4. No filter is used during the use of the broadband cavity enhanced absorption spectroscopy system. The obtained spectra are corrected to obtain the spectrum after deducting stray light. ,Right now , the influence of stray light in the measurement of broadband cavity enhanced absorption spectroscopy is deducted.

2. A computer-readable storage medium storing a computer program, wherein when the computer program is executed by a processor, the processor executes the steps of the method according to claim 1.

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