Reincidence-adjustable integral cavity gas measurement system and detection method

Abstract

The invention relates to the technical field of gas measurement, and discloses an adjustable re-incidence integral cavity gas measurement system, which comprises a laser emission module, an adjustable re-incidence module, a resonant cavity assembly and a signal acquisition and analysis module, and is characterized in that the adjustable re-incidence module comprises a first reflector, a second reflector and a first re-reflector; the resonant cavity assembly comprises an optical resonant cavity, a front high-reflectivity mirror and a rear high-reflectivity mirror, the front high-reflectivity mirror and the rear high-reflectivity mirror are arranged at the front end and the rear end of the optical resonant cavity respectively, the signal acquisition and analysis module comprises a converging lens, a photoelectric detector and a terminal, and a data acquisition card is arranged in the terminal. The signal output end of the photoelectric detector is connected with the signal input end of a data acquisition card in the terminal; the laser output by the laser emission module is reflected to the second reflector through the first reflector, and is reflected to the plane of the front high-reflectivity mirror at the front end of the resonant cavity through the second reflector. The precision, sensitivity and stability of gas measurement can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of gas measurement, and particularly to an integral cavity gas measurement system with adjustable re-incidence and a detection method therefor. Background Art

[0002] At present, the accuracy of domestic greenhouse gas measurement equipment is quite different from that of foreign equipment. The technical gap is mainly manifested in problems such as low spectral resolution, insufficient detection sensitivity, and susceptibility to water vapor and aerosols. The mainstream greenhouse gas monitoring technology is based on the interaction between light and gas components, and through spectral analysis algorithms combined with opto-mechatronic and computer engineering technologies, non-contact quantitative inversion of greenhouse gas concentration is achieved. Common monitoring technologies include non-dispersive infrared beam technology, off-axis integrated cavity output spectroscopy technology, Fourier transform spectroscopy technology, differential absorption lidar technology, etc.

[0003] Among them, the off-axis integrated cavity output spectroscopy technology uses an off-axis integrated cavity to reflect the light beam in the sample. After multiple reflections, a diffraction spectrum is formed at the output port. However, the cavity mode noise has a greater impact, and it is difficult to control the injection position and angle of the reflected light, resulting in serious optical interference. Summary of the Invention

[0004] In order to overcome the deficiencies of the prior art, the purpose of the present invention is to provide an integral cavity gas measurement system with adjustable re-incidence and a detection method therefor, which can improve the accuracy, sensitivity and stability of gas measurement.

[0005] The present invention is implemented by the following technical solutions: An adjustable re-incidence integrated cavity gas measurement system includes a laser emission module, an adjustable re-incidence module, a resonant cavity assembly, and a signal acquisition and analysis module. The adjustable re-incidence module includes a first reflector, a second reflector, and a first re-reflector. The resonant cavity assembly includes an optical resonant cavity, a front high reflector, and a rear high reflector. The front high reflector and the rear high reflector are respectively arranged at the front end and the rear end of the optical resonant cavity. The signal acquisition and analysis module includes a converging lens, a photodetector, and a terminal. A data acquisition card is arranged in the terminal. The signal output end of the photodetector is connected to the signal input end of the data acquisition card in the terminal. The laser output by the laser emission module is reflected by the first reflector to the second reflector, and then reflected by the second reflector to the plane of the front high reflector at the front end of the resonant cavity. Part of the laser is transmitted into the resonant cavity, and most of the remaining laser cannot enter the resonant cavity due to the reflection of the plane of the front high reflector. The first re-reflector re-reflects the laser reflected by the plane of the front high reflector into the resonant cavity. The emitted laser is injected into the cavity at the plane of the front high reflector and reaches the concave surface of the rear high reflector. After being reflected, it returns to the concave surface of the front high reflector and is reflected again to the concave surface of the rear high reflector. A piezoelectric ceramic is used to adjust the distance between the first re-reflector and the front high reflector in a jitter manner to suppress the generation of interference noise. The two beams of light are incident on the resonant cavity in sequence and then transmitted through the rear high reflector. The converging lens focuses the transmitted signal, and the photodetector performs photoelectric conversion. Finally, the terminal collects and processes the signal.

[0006] Further, an air outlet and an air inlet are connected to the upper part of the resonant cavity. The air outlet is connected to an air extraction pump, and the air extraction pump is used to extract the gas in the resonant cavity to maintain the air pressure in the resonant cavity, which is convenient for continuous collection of the gas to be measured.

[0007] Further, the laser emission module includes a signal generation module, a laser unit control module, and a tunable wavelength laser diode. The laser unit control module is used to control the current and temperature of the tunable wavelength laser diode to drive the tunable wavelength laser diode to output laser.

[0008] Further, the angle of the first re-reflector can be adjusted so that the laser reflected by the plane of the front high reflector is re-reflected into the resonant cavity at a sufficient off-axis angle.

[0009] An adjustable re-incidence integrated cavity gas measurement and adjustment method uses the adjustable re-incidence integrated cavity gas measurement system, and includes the following steps:

[0010] Step 1: Stick printed circular papers with central holes at both ends of the cavity of the resonant cavity to determine the cavity axis.

[0011] Step 2: Use a He-Ne laser to emit laser light that passes through the first reflector and the second reflector in sequence. The laser beam is adjusted to pass through the central drill holes of two printed circular papers, achieving a rough alignment of the cavity.

[0012] Step 3: Remove the printed circular papers, install the front high reflector and the rear high reflector into two hexagonal adjustment mounts respectively, and fix them with retaining rings. Install and adjust the first adjustment mount with the front high reflector so that the laser beam of the front high reflector coincides with the light spot on the first reflector. At the same time, observe the diffraction rings on the whiteboard and make fine adjustments to ensure that the incident beam is centered in the rings.

[0013] Step 4: Install the second adjustment mount with the rear high reflector and make fine adjustments to the rear high reflector so that the spot pattern converges around the first pattern caused by the rear high reflector. As the two reflectors are gradually aligned, specific changes can be observed, and finally, a concentric ring interference pattern appears, achieving the calibration of the optical resonator.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0015] 1. An adjustable re-incident integrated cavity gas measurement system of the present invention improves the utilization efficiency of laser light significantly at the input end by re-injecting useless reflected light into the optical resonator, and improves the signal flatness and signal-to-noise ratio at the receiving end, thereby improving the accuracy, sensitivity, and stability of gas measurement.

[0016] 2. An adjustable re-incident integrated cavity measurement adjustment method of the present invention is used to perform optical alignment on the resonator of the adjustable re-incident integrated cavity gas measurement system before use, thereby improving the measurement accuracy of the system. Description of the Drawings

[0017] Figure 1 is a schematic structural diagram of the adjustable re-incident integrated cavity gas measurement system of the present invention;

[0018] Figure 2 is a schematic adjustment diagram of the adjustable re-incident integrated cavity gas measurement system of the present invention.

[0019] In the figure: Laser emission module - 1; Tunable wavelength laser diode - 2; Optical resonator - 3; Converging lens - 6; Photoelectric detector - 7; Terminal - 8; He-Ne laser - 9; First reflector - 10; Second reflector - 11; First re-reflector - 12; Whiteboard - 13; Piezoelectric ceramic - 14; Front high reflector - 41; Rear high reflector - 42; Gas outlet - 51; Gas inlet - 52. Detailed Embodiments

[0020] The following describes the embodiments of the present invention through specific examples. Those skilled in the art can easily understand the other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, without conflict, the following embodiments and the features in the embodiments can be combined with each other.

[0021] The object of the present invention is to provide an adjustable re - incident integrated cavity gas measurement system and detection method in view of the defects of the prior art.

[0022] Embodiment 1

[0023] An adjustable re - incident integrated cavity gas measurement system provided in this embodiment is shown in reference to Figure 1 and includes a laser emission module 1, an adjustable re - incident module, a resonant cavity assembly, and a signal acquisition and analysis module. The laser emission module 1 includes a signal generation module, a laser unit control module, and a tunable - wavelength laser diode 2. The laser unit control module is used to control the current and temperature of the tunable - wavelength laser diode 2 to drive the tunable - wavelength laser diode 2 to output laser. The adjustable re - incident module includes a first reflector 10, a second reflector 11, and a first re - reflector 12. The first re - reflector 12 is mounted on a piezoelectric ceramic 14 and is used to adjust the distance between the first re - reflector 12 and the front high - reflector 41. The resonant cavity assembly includes an optical resonant cavity 3, a front high - reflector 41, and a rear high - reflector 42. The front high - reflector 41 and the rear high - reflector 42 are respectively arranged at the front end and the rear end of the optical resonant cavity 3. The signal acquisition and analysis module includes a converging lens 6, a photodetector 7, and a terminal 8. In this embodiment, the terminal 8 is a computer, and a data acquisition card is set in the computer. The signal output end of the photodetector 7 is connected to the signal input end of the data acquisition card in the computer.

[0024] When the adjustable re-incident integrating cavity gas measurement system is working, the laser output by the laser emitting module 1 is reflected by the first reflector 10 to the second reflector 11, and is reflected by the second reflector 11 to the plane of the front high reflector 41 at the front end of the resonant cavity 3. Part of the laser is transmitted into the resonant cavity 3, and most of the remaining laser cannot enter the resonant cavity 3 due to the plane reflection of the front high reflector 41. The laser reflected from the plane of the front high reflector 41 is reflected again by the first re-reflector 12 into the resonant cavity 3; after the laser is injected into the cavity from the plane of the front high reflector 41 and reaches the concave surface of the rear high reflector 42, it is reflected back to the concave surface of the front high reflector 41 and reflected again to the concave surface 41 of the rear high reflector, thereby realizing back and forth emission. When the fully off-axis condition is met, dense light spots are formed on the concave surfaces of the front and rear high-reflection mirrors, and at the same time, a large amount of weak transmitted light is emitted through the rear high-reflection mirror to form a detection signal; since the signal light in the resonant cavity 3 is divided into two paths, namely the transmitted light and the reflected light; the transmitted light and the reflected light are reflected back and forth by the concave surfaces of the front and rear high-reflection mirrors in the resonant cavity 3, and both can form a uniform light spot distribution on the surfaces of the front and rear high-reflection mirrors, and then the piezoelectric ceramic 14 is used to realize the dither adjustment of the distance between the first re-reflection mirror 12 and the front high-reflection mirror, change the phase of the laser, and further suppress the generation of interference noise. The angle of the first re-reflection mirror 12 can also be adjusted so that the laser reflected from the plane of the front high-reflection mirror 41 is reflected back into the resonant cavity 3 at a fully off-axis angle. The two paths of light are incident on the resonance 3 in turn and then pass through the rear high reflective mirror 42. The transmission signal is focused by the converging lens 6 and photoelectrically converted by the photodetector 7. Finally, the data acquisition card and the terminal collect and process the signal. By injecting the useless reflected light into the optical resonance cavity, the utilization efficiency of the laser is greatly improved at the input end, and the signal flatness and signal-to-noise ratio are improved at the receiving end, thereby improving the accuracy, sensitivity and stability of gas measurement.

[0025] The upper part of the resonance cavity 3 is connected with an air outlet 51 and an air inlet 52. The air outlet 51 is connected to an air pump, and the air in the resonance cavity 3 is pumped out by the air pump to maintain the air pressure in the resonance cavity 3, so as to facilitate the continuous collection of the gas to be tested.

[0026] A method for adjusting the measurement of an adjustable re-incidence integral cavity is used to optically align the resonant cavity 3 before the use of the adjustable re-incidence integral cavity gas measurement system, referring to Figure 2 As shown, it includes the following steps:

[0027] Step 1: Paste a printed circular paper with a central hole on both ends of the cavity of the resonant cavity 3 to determine the cavity axis;

[0028] Step 2: Using He-Ne laser 9 to emit laser light through first reflector 10 and second reflector 11 in sequence, the laser beam is adjusted to pass through the central drilling holes of two printed round papers to achieve rough alignment of the cavity;

[0029] Step 3: Remove the printed round paper, install the front high reflector 41 and the rear high reflector 42 into two hexagonal adjustment brackets respectively, and fix them with retaining rings; install and adjust the first adjustment bracket with the front high reflector 41 to make the laser beam of the front high reflector 41 coincide with the light spot on the first mirror 10. At the same time, observe the diffraction rings on the whiteboard 13 and make fine adjustments to ensure that the incident beam is centered in the rings;

[0030] Step 4: Install the second adjustment bracket with the rear high reflector 42 and make fine adjustments to the rear high reflector 42 so that the spot pattern converges with the first pattern caused by the rear high reflector 42 as the center; as the two mirrors are gradually aligned, specific changes can be observed, and finally the appearance of a concentric ring interference pattern is achieved, realizing the calibration of the optical resonator 3 and improving the measurement accuracy of the system.

[0031] In addition, it should be understood that although this specification is described according to embodiments, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. An adjustable re-incidence integrating cavity gas measurement system, characterized in that: The invention comprises a laser emission module (1), an adjustable re-incidence module, a resonant cavity component and a signal acquisition and analysis module. The adjustable re-incidence module comprises a first reflector (10), a second reflector (11) and a first re-reflector (12). The resonant cavity component comprises an optical resonant cavity (3), a front high reflector (41) and a rear high reflector (42). The front high reflector (41) and the rear high reflector (42) are respectively arranged at the front end and the rear end of the optical resonant cavity (3). The signal acquisition and analysis module comprises a converging lens (6), a photoelectric detector (7) and a terminal (8). A data acquisition card is arranged in the terminal (8). The signal output end of the photoelectric detector (7) is connected to the signal input end of the data acquisition card in the terminal (8). The laser output of the laser emission module (1) is reflected to the second reflector (11) through the first reflector (10), and the second reflector (11) reflects to the front end of the resonant cavity (3). The plane of the front high reflector (41) is reflected by the plane of the front high reflector (41), part of the laser light is transmitted into the resonant cavity (3), and most of the remaining laser light cannot enter the resonant cavity (3) due to the plane reflection of the front high reflector (41). The laser light reflected by the plane of the front high reflector (41) is reflected again by the first re-reflector (12) and enters the resonant cavity (3); the emitted laser light is injected into the cavity from the plane of the front high reflector (41) and reaches the concave surface of the rear high reflector (42), then reflected back to the concave surface of the front high reflector (41), and reflected again to the concave surface of the rear high reflector (41), and the jitter adjustment of the distance between the first re-reflector (12) and the front high reflector (41) is realized by using piezoelectric ceramics to suppress the generation of interference noise, the two paths of light are incident on the resonance in sequence and then transmitted through the rear high reflector, the transmission signal is focused by the converging lens (6), and the photoelectric conversion is performed by the photoelectric detector (7), and finally the signal is collected and processed by the terminal (8).

2. The adjustable re-incident integrating cavity gas measurement system according to claim 1, characterized in that: The resonant cavity (3) is connected to an air outlet (51) and an air inlet (52), and the air outlet (51) is connected to an air pump, and the air in the resonant cavity (3) is pumped out by the air pump to maintain the air pressure in the resonant cavity (3), thereby facilitating the continuous collection of the gas to be measured.

3. The adjustable re-incident integrating cavity gas measurement system according to claim 2, characterized in that: The laser emission module (1) comprises a signal generating module, a laser unit control module and a laser diode (2) with a tunable wavelength. The laser unit control module is used to control the current and temperature of the laser diode (2) with a tunable wavelength, and drive the laser diode (2) with a tunable wavelength to output laser light.

4. The adjustable re-incident integrating cavity gas measurement system according to claim 3, characterized in that: The angle of the first re-reflecting mirror (12) can be adjusted so that the laser light reflected from the plane of the front high-reflecting mirror (41) is re-reflected at a sufficiently off-axis angle and enters the resonant cavity (3).

5. A method for adjusting gas measurement of an integrating cavity with adjustable re-incidence, using the integrating cavity with adjustable re-incidence gas measurement system according to any one of claims 1 to 4, characterized in that: The following steps are involved: Step 1: Paste a printed circular paper with a central hole on both ends of the cavity of the resonant cavity (3) to determine the cavity axis; Step 2: Using a He-Ne laser (9) to emit laser light, the laser beam is adjusted to pass through the central drilling holes of the two printed round papers to achieve rough alignment of the cavity; Step 3: Remove the printed circular paper, install the front high reflector (41) and the rear high reflector (42) into two hexagonal adjustment frames respectively, and fix them with pressure rings; install and adjust the first adjustment frame equipped with the front high reflector (41) so that the laser beam of the front high reflector (41) coincides with the light spot on the first reflector (10), and observe the diffraction ring on the white board (13) at the same time, and make fine adjustments to ensure that the incident beam is centered in the ring; Step 4: Install a second adjustment frame equipped with a rear high reflective mirror (42), and finely adjust the rear high reflective mirror (42) so that the speckle pattern is concentrated around the first pattern caused by the rear high reflective mirror (42); as the two reflective mirrors are gradually aligned, specific changes can be observed, and finally a concentric ring interference pattern is achieved, thereby achieving calibration of the optical resonant cavity (3).

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