CN111413321A - An optical fiber Raman spectroscopic gas analysis device - Google Patents

Abstract

The invention discloses an optical fiber Raman spectroscopy gas analysis device, belonging to the technical field of gas analysis. The device comprises: a laser, a beam coupling device, a gas sample chamber, a collimating beam splitting device and a photoelectric imaging receiving device; Coupling into the gas sample chamber; Raman scattering is generated by the interaction between the laser and the gas to be tested in the core of the hollow fiber; the collimating beam splitter collimates the mixed beam and separates the laser, and transmits the beam containing only scattered signals to the photoelectric The imaging receiving device; the photoelectric imaging receiving device performs digital spatial filtering on the forward scattered signal to obtain the Raman spectrum of the gas to be measured. The invention generates an enhanced Raman scattering signal by interacting the gas to be tested with the laser in the hollow core fiber, collects the forward signal by using a photoelectric imaging receiving device, and implements digital spatial filtering to reduce the background signal of the gas sample chamber, thereby solving the problem of pulling The problem of difficult detection of trace components in Mann gas analysis has improved the sensitivity of the system detection.

Description

An optical fiber Raman spectroscopic gas analysis device

technical field

The invention belongs to the technical field of gas analysis and detection, and more particularly relates to an optical fiber Raman spectroscopy gas analysis device.

Background technique

The phenomenon in which excitation light is scattered by molecules and the frequency of the scattered light is changed is called Raman scattering. When the excitation light intensity is weak, the scattered light intensity is proportional to the excitation light intensity and the number of scattering molecules. This kind of Raman scattering is often called linear Raman scattering or spontaneous Raman scattering. The signal intensity has a linear correlation with the number of scattering molecules. , making Raman scattering widely used in chemical analysis. Due to the relatively small Raman cross section and molecular number density of the gas, the intensity of Raman scattering is very weak, and the gas detection based on Raman spectroscopy is limited. It is particularly important to improve the intensity of the gas signal. In recent years, the research and development of gas Raman detection has been devoted to improving the detection sensitivity of the device and increasing its application range. The main methods include enhancing the Raman signal and reducing the signal background. For gas detection, the main technical methods for signal enhancement currently include hollow-core fiber enhancement, resonant cavity enhancement and multi-optical path enhancement. Among them, the hollow core fiber not only acts as a sample gas chamber, but also can significantly increase the Raman scattering signal, which has high application value.

In fiber-enhanced Raman spectroscopy, the choice of fiber has a great influence on the signal background and signal-to-noise ratio. Most of the published results use bandgap hollow-core photonic crystal fibers or metal-coated capillaries. However, due to the small core diameter of the former, the gas flow is slow, and the small and dense cladding holes are easy to retain the gas, which is not conducive to the rapid renewal of the gas; the latter has high transmission loss, and the excitation light leaking into the glass cladding will also bring fluorescence and Silica Raman background. Finding a more suitable hollow-core fiber is a work focus.

A method for detecting human respiratory substances based on hollow-core photonic crystal fiber and Raman spectroscopy (Patent No. CN107421942A) combines fiber enhancement and cavity enhancement technology. Fiber Bragg gratings are arranged at both ends of the hollow-core fiber to form a resonant cavity. Oscillating back and forth in the fiber increases the number of molecules involved in Raman scattering, thereby increasing the intensity of the gas signal, but imperfect coupling can also lead to increased fluorescence and silica Raman background. Hollow-core fiber SERS probe preparation method and harmful gas detection system (patent number CN109239050A) combine fiber enhancement and surface-enhanced Raman spectroscopy technology, assemble gold and silver nanoparticles on the inner surface of the core of the hollow fiber, or assemble the prepared Raman detection is carried out after the metal nanoparticles are evenly mixed with the sample to be tested to form a suspended metal nanoparticle substrate, and the signal can be greatly improved, but the preparation cost of nanoparticles is high, and any pollution on the surface of nanoparticles (such as the previous gas measurement adsorption) will affect the accuracy of the measurement and is not suitable for repeated online detection.

SUMMARY OF THE INVENTION

Aiming at the above defects or improvement needs of the prior art, the present invention provides an optical fiber Raman spectroscopy gas analysis device, thereby solving the technical problems of high signal background and low analysis sensitivity of the gas analysis system.

In order to achieve the above object, according to an aspect of the present invention, a fiber Raman spectroscopy gas analysis device is provided, the device includes: a laser, a beam coupling device, a gas sample chamber, a collimating beam splitting device, and a photoelectric imaging receiving device;

The beam coupling device is used for coupling the laser light emitted by the laser into the gas sample chamber;

The gas sample chamber is used for reacting the coupled laser light with the gas molecules to be tested in the hollow fiber core of the gas sample chamber to generate Raman scattering, and mixing the forward scattered signal with the laser light delivering the light beam to the collimating beam splitting device;

The collimating beam splitting device is used for collimating the mixed light beam to separate the laser light in the mixed light beam, and sending the light beam containing only the forward scattered signal to the photoelectric imaging receiving device;

The photoelectric imaging receiving device is used for collecting the forward scattering signal, and performing digital spatial filtering on the forward scattering signal to obtain the Raman spectrum of the gas to be measured.

Preferably, the beam coupling device includes a laser line filter and a focusing coupling lens; the laser line filter is used for filtering out the fluorescent components in the laser light generated by the laser; the focusing coupling lens is used for focusing the laser light and coupling the laser light into the hollow core fiber.

Preferably, the gas sample chamber includes a gas storage bottle, a pipeline, a hollow-core optical fiber, a fixture and a vacuum pump;

The gas storage bottle is used to store the gas to be measured; the hollow-core optical fiber is used to generate Raman scattering by the action of the gas to be measured and the laser; the fixing device is used to fix both ends of the hollow-core optical fiber; The vacuum pump is used to evacuate the gas in the hollow-core optical fiber when the gas to be tested is updated; the gas storage bottle and the hollow-core optical fiber are connected through the pipeline, and the hollow-core optical fiber and the vacuum pump pass through the The pipeline is connected, and the pipeline is used to transport the gas to be tested.

Preferably, the gas sample chamber further includes a solenoid valve; the solenoid valve is arranged between the gas storage bottle and the hollow fiber, and the solenoid valve is used to control the on-off of the gas circuit.

Preferably, the gas sample chamber further includes an air pressure gauge; the air pressure gauge is arranged between the solenoid valve and the hollow fiber, and the air pressure gauge is used to display the air pressure of the gas to be measured in the pipeline.

Preferably, the hollow-core optical fiber is a hypocycloid Kagomé hollow-core optical fiber.

Preferably, the collimating beam splitting device comprises a collimating lens, a dichroic mirror, a beam blocking device and a long pass filter;

The collimating lens is used to convert the mixed beam output from the gas sample chamber into a collimated parallel beam; the dichroic mirror is used to separate the laser light in the mixed beam from the forward scattered signal; the The beam blocking device is used for absorbing the laser light in the mixed light beam reflected by the dichroic mirror; the long-pass filter is used for filtering out the residual laser light in the forward scattered signal.

Preferably, the photoelectric imaging receiving device includes an optical radiation collecting lens, a spectrometer, a detector and a data processing device;

The spectrometer is used to obtain the spectral distribution of the forward scattered signal collected by the optical radiation collecting lens and passed through the long-pass filter; the detector is used to image the spectral distribution of the forward scattered signal ; The data output end of the detector is connected to the data processing device, and the data processing device is used to control the collection and processing of the forward scattered signal, implement digital spatial filtering, and obtain the Raman of the gas to be measured. spectrum.

Preferably, the data processing device is further configured to adjust the focus of the optical radiation collecting lens, so that the forward scattered signal is converged on the detector.

Preferably, the detector is a CCD array detector.

In general, compared with the prior art, the above technical solutions conceived by the present invention have the following beneficial effects:

1. The present invention obtains a spectrum with low background by combining forward Raman scattering signal collection and imaging spectrometer digital spatial filtering, effectively reducing signal background and noise, improving the sensitivity of analysis, and being suitable for the detection of trace component gases at the same time, It has broad application prospects in environmental gas sensing, breathing gas analysis and industrial monitoring;

2. The present invention adopts the collection of forward Raman scattering signals, which avoids the Raman fluorescence background generated during laser coupling, reduces noise, and improves signal-to-noise ratio;

3. The present invention uses the hypocycloid Kagomé hollow-core optical fiber to reduce the transmission loss, and the core mode and the cladding mode have only a small amount of spatial overlap;

4. The present invention uses an imaging spectrometer to implement digital spatial filtering, which further simplifies the experimental device.

The difficulty of adjusting the optical path is reduced.

Description of drawings

1 is a schematic structural diagram of an embodiment of the present invention;

FIG. 2 is a schematic structural diagram of a gas sample chamber according to an embodiment of the present invention.

In all figures, the same reference numerals are used to denote the same elements or structures, wherein: laser 1; laser line filter 2; focusing coupling lens 3; gas sample chamber 4; collimating lens 5; dichroic mirror 6; beam blocking device 7; long-pass filter 8; optical radiation collecting lens 9; spectrometer 10; detector 11; data processing device 12; gas cylinder 13; pipeline 14; solenoid valve 15; ; Hollow core fiber 18; Vacuum pump 19.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

As shown in FIG. 1, the present invention proposes a fiber Raman spectroscopy gas analysis device, the device includes: a laser 1, a beam coupling device, a gas sample chamber 4, a collimating beam splitting device and a photoelectric imaging receiving device; the The beam coupling device is used to couple the laser light emitted by the laser 1 into the gas sample chamber; the gas sample chamber 4 is used to couple the coupled laser to the hollow fiber core of the gas sample chamber 4 The action of the gas molecules to be tested in 18 produces Raman scattering, and the mixed beam of the forward scattered signal and the laser is sent to the collimating beam splitting device; the collimating beam splitting device is used to split the mixed beam After collimation, the laser light in the mixed beam is separated, and the beam containing only the forward scattered signal is sent to the photoelectric imaging receiving device; the photoelectric imaging receiving device is used to collect the forward scattered signal, and performing digital spatial filtering on the forward scattered signal to obtain the Raman spectrum of the gas to be measured.

In an embodiment of the present invention, considering the volume and cost of the equipment, the laser used in the present invention is a 532nm narrow linewidth laser, the continuous output power can reach 200mW, and the beam quality factor ^M2 is less than 1.2, which can pass through the The focusing coupling lens 3 is well matched to the conduction mode of the hollow core fiber 18 . The power of the laser has a linear relationship with the intensity of Raman scattering. The higher the power, the greater the intensity of Raman scattering.

To further illustrate, the beam coupling device includes a laser line filter 2 and a focusing coupling lens 3; the laser line filter 2 is used to filter out the fluorescent components in the laser light generated by the laser 1; the focusing coupling lens 3 is used to focus and couple the laser light into the hollow core fiber 18 . As shown in FIG. 1 , in an embodiment of the present invention, the focusing coupling lens 3 has a focal length of 60 mm, and the laser light generated by the laser 1 is filtered by the laser line filter 2 to filter out optical elements such as laser gain medium generation or window and so on. The generated fluorescent component, the focusing coupling lens 3 converges the laser light to match the numerical aperture of the hollow core fiber 18, and couples the laser light into the hollow core fiber 18 with high efficiency, so that the Raman scattering occurs when the laser interacts with the gas molecules to be measured.

To further illustrate, the gas sample chamber 4 includes a gas storage cylinder 13, a pipeline 14, a solenoid valve 15, a barometer 16, a hollow fiber 18, a fixing device 17 and a vacuum pump 19; the gas storage cylinder 13 is used for storing the the gas to be measured; the hollow-core optical fiber 18 is used to generate Raman scattering by the action of the gas to be measured and the laser; the fixing device 17 is used to fix both ends of the hollow-core optical fiber 18; the vacuum pump 19 is used to When the gas to be measured is updated, the gas in the hollow-core optical fiber 18 is emptied; the gas storage bottle 13 and the hollow-core optical fiber 18 are connected through the pipeline 14 , and the hollow-core optical fiber 18 and the vacuum pump 19 pass through The pipeline 14 is connected, and the pipeline 14 is used to transport the gas to be measured. A specific embodiment of the gas sample chamber 4 of the present invention is shown in FIG. 2 , the gas to be tested in the gas storage bottle 13 can be filled into the hollow fiber 18 through the pipeline 14 , and the solenoid valve 15 controls The gas path is switched on and off to realize the rapid change of air pressure and gas type in the hollow-core optical fiber 18 , and the air pressure gauge 16 is used to indicate the air pressure. Both ends of the hollow-core optical fiber 18 are installed on the fixing device 17 with an optical window, and the gas in the hollow-core optical fiber 18 is evacuated by the vacuum pump 19 when the gas is renewed. It should be noted that, in order to achieve a compact structure of the device, the hollow-core optical fiber 18 can be wound into a circular ring with a radius of not less than 10 cm.

To further illustrate, the hollow core optical fiber 18 is a hypocycloid Kagomé hollow core optical fiber. The present invention selects the hollow core optical fiber which suppresses the coupling light guide mechanism, the hypocycloid Kagomé hollow core optical fiber as the preferred embodiment of the present invention, the optical fiber cladding is a large-spacing Kagomé lattice structure, and the fiber core is a hypocycloid shape. This fiber structure can suppress the coupling of the core conduction mode to the cladding, the core mode and the cladding mode have only a small amount of spatial overlap, the Raman/fluorescence background excited by the cladding mode is weak, and the background of the obtained spectrum is relatively flat. When the fiber length is less than the fiber attenuation length (the reciprocal of the attenuation coefficient), the forward Raman scattering intensity is equivalent to the backward Raman scattering intensity. Compared with the backward direction, the forward scattering collection structure adopted in the present invention avoids the excitation light coupling. The Raman/fluorescence background generated at the fiber entrance reduces the spectral background noise and improves the signal-to-noise ratio. There is still a small amount of Raman/fluorescence background from cladding modes in the signal, which can be further reduced by digital spatial filtering. The usual spatial filter consists of a converging lens, a spatial aperture at the focal point, and a collimating lens, which increases the difficulty of adjusting the optical path. The shape and position of the spatial aperture are not necessarily consistent with the Raman scattering spot generated by the conduction mode, and There are high requirements on the stability of the device.

To further illustrate, the collimating beam splitting device includes a collimating lens 5, a dichroic mirror 6, a beam blocking device 7 and a long-pass filter 8; the collimating lens 5 is used to separate the gas sample chamber 4. The output mixed beam becomes a collimated parallel beam; the dichroic mirror 6 is used to separate the laser light in the mixed beam from the forward scattered signal; the beam blocking device 7 is used to absorb the dichroic The laser light in the mixed beam reflected by the mirror 6; the long-pass filter 8 is used to filter out the residual laser light in the forward scattered signal to obtain a light beam containing only scattered signals. It should be noted that the focal length of the collimating lens 5 is 40mm. As shown in FIG. 1 , the device adopts a forward scattering structure to collect Raman scattering signals, and the mixed beam of Raman scattering signals and laser light passes through the collimating lens. 5 After collimation, it is roughly separated by the dichroic mirror 6, and the transmitted laser light is blocked and absorbed by the beam blocking device 7. The transmitted mixed beam passes through the long-pass filter 8 to filter out residual laser light.

To further illustrate, the photoelectric imaging receiving device includes an optical radiation collecting lens 9, a spectrometer 10, a detector 11 and a data processing device 12; the spectrometer 10 is used to obtain the transmitted data collected by the optical radiation collecting lens 9 The spectral distribution of the forward scattered signal of the long-pass filter 8; the detector 11 is used to image the spectral distribution of the forward scattered signal; the data output end of the detector 11 is connected to the data The processing device 12, the data processing device 12 is used to control the collection and processing of the forward scattered signal, implement digital spatial filtering, and obtain the Raman spectrum of the gas to be measured. As shown in FIG. 1 , in an embodiment of the present invention, the optical radiation collecting lens 9 of the spectrometer 10 collects forward scattered signals, and finally images them on the detector 11 , and the data output end of the detector 11 is connected to the The computer 12 is connected, and the collection and processing of signals are controlled by software. In the image mode, the optical radiation collecting lens 9 is adjusted so that the collected Raman scattering signals of the gas to be measured in the hollow core fiber 18 are clearly converged to the desired location. onto the detector 11, followed by digital spatial filtering and data acquisition. The data processing device 12 in the present invention is a computer. By analyzing the collected low-background Raman spectrum, the composition of the gas to be measured can be obtained. In contrast, the device adopts the method of digital spatial filtering of the imaging spectrometer, which can realize the automatic focusing of the spectrometer and the automatic selection of the spectral integration area through the control software of the CCD array detector, and reduce the Raman/fluorescence generated by the cladding mode. At the same time, the experimental device is simplified and the experimental operation is convenient. For the detection of trace gas, the background in the Raman spectrum is easy to annihilate the weak signal, and the hollow-core optical fiber selected in the present invention has a low spatial overlap ratio of the core mode/cladding mode. It should be noted that the transmission frequency band of the hollow-core fiber is 500-700 nm, and under the excitation of 532 nm laser, the corresponding Stokes Raman shift range is 0-4511 cm ^-1 , which can simultaneously collect hydrogen gas including hydrogen. Raman signals of almost all gas-based vibration bands; the core diameter is 30±1μm, which is several times larger than the core diameter of the bandgap hollow-core photonic crystal fiber, which is convenient for gas renewal and realizes fast online detection; the transmission loss of the 532nm laser is 30dB/km±10, fiber length is 2m.

For further explanation, the data processing device 12 is also used for adjusting the focus of the optical radiation collecting lens 9 , so that the forward scattered signal is clearly focused on the detector 11 .

For further explanation, the detector 11 is a CCD array detector. It should be noted that the CCD array detector has two modes: image and spectrum. Using the image mode, the optical radiation collecting lens 8 can be adjusted to make the Raman scattering generated by the gas sample to be measured in the hollow fiber 18. It can be clearly imaged on the CCD array detector. According to the results of the image mode, select the pixel row corresponding to the Raman scattering signal generated by the conduction mode of the hollow-core fiber for integration, so as to avoid the increase of the Raman/fluorescence radiation signal generated by the cladding mode. background. The forward Raman scattering collection combined with the CCD digital spatial filtering of the imaging spectrometer can significantly reduce the Raman/fluorescence background of the spectral signal, improve the signal-to-noise ratio of the device, and provide favorable support for the detection of trace components. Compared with the pinhole component spatial filter, the imaging spectrometer digital spatial filter adopted by the device further simplifies the experimental device and reduces the difficulty of adjusting the optical path.

Those skilled in the art can easily understand that the above are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, etc., All should be included within the protection scope of the present invention.

Claims (10)

1. An optical fiber Raman spectroscopy gas analysis device, characterized in that the device comprises: a laser, a beam coupling device, a gas sample chamber, a collimated beam splitting device and a photoelectric imaging receiving device; The beam coupling device is used for coupling the laser light emitted by the laser into the gas sample chamber; The gas sample chamber is used for reacting the coupled laser light with the gas molecules to be tested in the hollow fiber core of the gas sample chamber to generate Raman scattering, and mixing the forward scattered signal with the laser light delivering the light beam to the collimating beam splitting device; The collimating beam splitting device is used for collimating the mixed light beam to separate the laser light in the mixed light beam, and sending the light beam containing only the forward scattered signal to the photoelectric imaging receiving device; The photoelectric imaging receiving device is used for collecting the forward scattering signal, and performing digital spatial filtering on the forward scattering signal to obtain the Raman spectrum of the gas to be measured. 2 . The optical fiber Raman spectroscopy gas analysis device according to claim 1 , wherein the beam coupling device comprises a laser line filter and a focusing coupling lens; the laser line filter is used to filter out the The fluorescent component in the laser light generated by the laser; the focusing coupling lens is used for condensing the laser light and coupling the laser light into the hollow core fiber. 3. An optical fiber Raman spectroscopy gas analysis device according to claim 1, wherein the gas sample chamber comprises a gas storage bottle, a pipeline, a hollow fiber, a fixing device and a vacuum pump; The gas storage bottle is used to store the gas to be measured; the hollow-core optical fiber is used to generate Raman scattering by the action of the gas to be measured and the laser; the fixing device is used to fix both ends of the hollow-core optical fiber; The vacuum pump is used to evacuate the gas in the hollow-core optical fiber when the gas to be tested is updated; the gas storage bottle and the hollow-core optical fiber are connected through the pipeline, and the hollow-core optical fiber and the vacuum pump pass through the The pipeline is connected, and the pipeline is used to transport the gas to be tested. 4 . The optical fiber Raman spectroscopy gas analysis device according to claim 3 , wherein the gas sample chamber further comprises a solenoid valve; the solenoid valve is arranged between the gas storage bottle and the hollow fiber. 5 . In between, the solenoid valve is used to control the opening and closing of the air passage. 5 . The optical fiber Raman spectroscopy gas analysis device according to claim 4 , wherein the gas sample chamber further comprises a barometer; the barometer is arranged between the solenoid valve and the hollow fiber. 6 . During the time, the air pressure gauge is used to display the air pressure of the gas to be measured in the pipeline. 6 . The optical fiber Raman spectroscopy gas analysis device according to claim 3 , wherein the hollow-core optical fiber is a hypocycloid Kagomé hollow-core optical fiber. 7 . 7. A kind of optical fiber Raman spectroscopy gas analysis device according to claim 1, is characterized in that: described collimating beam splitting device comprises collimating lens, dichroic mirror, beam blocking device and long pass filter; The collimating lens is used to convert the mixed beam output from the gas sample chamber into a collimated parallel beam; the dichroic mirror is used to separate the laser light in the mixed beam from the forward scattered signal; the The beam blocking device is used for absorbing the laser light in the mixed light beam reflected by the dichroic mirror; the long-pass filter is used for filtering out the residual laser light in the forward scattered signal to obtain a light beam containing only scattered signal. 8 . The optical fiber Raman spectroscopy gas analysis device according to claim 7 , wherein the photoelectric imaging receiving device comprises an optical radiation collecting lens, a spectrometer, a detector and a data processing device; 8 . The spectrometer is used to obtain the spectral distribution of the forward scattered signal collected by the optical radiation collecting lens and passed through the long-pass filter; the detector is used to image the spectral distribution of the forward scattered signal ; The data output end of the detector is connected to the data processing device, and the data processing device is used to control the collection and processing of the forward scattered signal, implement digital spatial filtering, and obtain the Raman of the gas to be measured. spectrum. 9 . The optical fiber Raman spectroscopy gas analysis device according to claim 8 , wherein the data processing device is further configured to adjust the focus of the optical radiation collecting lens, so that the forward scattered signal is converged to the desired location. 10 . on the detector. 10 . The optical fiber Raman spectroscopy gas analysis device according to claim 8 , wherein the detector is a CCD array detector. 11 .

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