CN115656099A - Method and system for measuring gas concentration - Google Patents
Method and system for measuring gas concentration Download PDFInfo
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- CN115656099A CN115656099A CN202211384532.0A CN202211384532A CN115656099A CN 115656099 A CN115656099 A CN 115656099A CN 202211384532 A CN202211384532 A CN 202211384532A CN 115656099 A CN115656099 A CN 115656099A
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Abstract
The application discloses a method and a system for measuring gas concentration. The method is applied to a gas concentration measuring system, and the gas concentration measuring system comprises: the system comprises an optical resonant cavity, a laser frequency locking system, a microwave source frequency reference scanning system and a signal acquisition and processing system, and the method specifically comprises the following steps: filling gas to be detected into the optical resonant cavity; and starting the laser to divide the laser into a first laser and a second laser. And then locking the frequency of the first laser by using the laser frequency locking system, tuning the frequency of the second laser by using the microwave source frequency reference scanning system, and measuring to obtain a spectrum signal. And processing and analyzing the spectrum signal by using the signal acquisition and processing system to obtain the gas concentration. Systems for gas concentration measurement are also disclosed in the present application. In the embodiment of the present application, high-precision measurement of the gas concentration is achieved.
Description
Technical Field
The present disclosure relates to gas detection, and more particularly, to a method and system for measuring gas concentration.
Background
With the continuous development of scientific technology, the gas concentration detection is more and more involved in the fields of industry, transportation industry and the like, and the trace gas detection has important significance for atmospheric chemistry research, environmental monitoring, semiconductor production and processing and the like.
At present, the traditional gas detection methods mainly comprise an electrochemical method, a mass spectrometry method, a gas chromatography method, a thermocatalysis method and the like. Although these conventional methods achieve measurement of gas to different degrees, they all perform sampling manually, and the instruments are expensive and complex to operate, and are often used for measurement of gas in laboratories, and it is difficult to meet the requirements of people on high sensitivity and high precision detection of gas concentration.
Therefore, how to realize high sensitivity and high precision measurement of gas concentration is an urgent technical problem to be solved.
Disclosure of Invention
In view of this, embodiments of the present application provide a method and a system for measuring a gas concentration, which aim to achieve high sensitivity and high accuracy of measurement of the gas concentration.
In a first aspect, an embodiment of the present application provides a method for measuring a gas concentration, where the method is applied to a gas concentration measurement system, and the gas measurement system includes: an optical resonant cavity, a laser frequency locking system, a microwave source frequency reference scanning system, and a signal acquisition and processing system, the method comprising:
filling gas to be detected into the optical resonant cavity;
starting a laser, and dividing the laser into a first laser and a second laser;
locking the frequency of the first laser with the laser frequency locking system;
tuning the frequency of the second laser by using the microwave source frequency reference scanning system, and measuring to obtain a spectrum signal;
and processing and analyzing the spectrum signal by using the signal acquisition and processing system to obtain the gas concentration.
Optionally, the tuning the frequency of the second laser by using the microwave source frequency reference scanning system, and measuring to obtain a spectrum signal specifically includes:
generating microwave signals with different frequencies by using the second laser;
amplifying the power of the microwave signal;
filtering high-order signals in the amplified microwave signals to obtain filtered microwave signals;
sideband lasers with different frequencies are generated by utilizing the filtered microwave signals and are introduced into the optical resonant cavity for spectrum detection.
Optionally, the locking the frequency of the first laser by using the laser frequency locking system specifically includes:
modulating the frequency of the first laser light output by the laser;
converting the first laser light from an optical signal to an electrical signal;
demodulating the electrical signal to obtain an error signal;
and converting the error signal into a control signal and feeding the control signal back to the laser, wherein the control signal is used for controlling the frequency of the first laser output by the laser.
Optionally, before the laser is started, the method further includes:
and setting a fixed pumping flow rate in the state that the gas to be measured is filled, and adjusting the flow rate of the gas to be measured at the gas inlet of the optical resonant cavity so as to maintain the pressure in the optical resonant cavity at a preset pressure value.
Optionally, the gas concentration measuring system further includes a temperature control system, the temperature control system includes a heating wire, and before the gas to be measured is filled into the optical resonant cavity, the method further includes:
starting the temperature control system to control the temperature of the optical resonant cavity;
and adjusting the heating current of the heating wire through proportional-integral control in the temperature control system so as to maintain the temperature in the optical resonant cavity at a preset temperature.
Optionally, the processing and analyzing the spectral signal by using the signal acquisition and processing system to obtain the gas concentration specifically includes:
converting the spectral signal into a voltage signal;
converting the voltage signal into a digital signal and converting the digital signal;
determining the gas concentration from the digital signal.
In a second aspect, an embodiment of the present application provides a system for gas concentration measurement, the system including:
the system comprises an optical resonant cavity, a laser frequency locking system, a microwave source frequency reference scanning system and a signal acquisition and processing system;
the optical resonant cavity is used for receiving gas to be detected;
the laser is used for emitting laser and dividing the laser into a first laser and a second laser;
the laser frequency locking system is used for locking the frequency of the first laser;
the microwave source frequency reference scanning system is used for tuning the frequency of the second laser and measuring to obtain a spectrum signal;
the signal acquisition and processing system is used for processing and analyzing the spectrum signal to obtain the gas concentration.
Optionally, the microwave source frequency reference scanning system includes:
the device comprises a microwave signal generating device, a signal amplifying device, a filtering device and a laser sideband generator;
the microwave signal generating device is used for generating microwave signals with different frequencies by using the second laser;
the signal amplification device is used for performing power amplification on the microwave signal and outputting the microwave signal;
the filtering device is used for filtering the high-order signal output by the signal amplifying device;
the laser sideband generator is used for generating sideband laser with different frequencies through the microwave signal and introducing the sideband laser into the optical resonant cavity for spectrum detection.
Optionally, the system further includes a pressure measuring device, where the pressure measuring device is configured to measure the pressure of the gas to be detected in the optical resonant cavity, and is configured to adjust the flow rate of the gas to be detected at the gas inlet of the optical resonant cavity according to a set fixed pumping flow rate in a state where the gas to be detected is filled, so as to maintain the pressure in the optical resonant cavity at a preset pressure value.
Optionally, the system further includes a temperature control system, the temperature control system includes a heating wire, and the temperature control system is configured to adjust a heating current of the heating wire through proportional-integral control, so as to maintain the temperature in the optical resonant cavity at a preset temperature.
The application provides a method and a system for measuring gas concentration, wherein the method is applied to a gas concentration measuring system, and the gas concentration measuring system comprises: the method comprises the following steps that an optical resonant cavity, a laser frequency locking system, a microwave source frequency reference scanning system and a signal acquisition and processing system are adopted, and when the method is executed, gas to be detected is filled into the optical resonant cavity; and starting the laser to divide the laser into a first laser and a second laser. And then locking the frequency of the first laser by a laser frequency locking system, tuning the frequency of the second laser by using a microwave source frequency reference scanning system, and measuring to obtain a spectrum signal. And finally, processing and analyzing the spectrum signal by using a signal acquisition and processing system to obtain the gas concentration. Therefore, the narrowing of the line width of the first laser is realized by locking the frequency of the first laser, and the frequency of the first laser can be kept stable so as to be convenient for measuring the gas concentration; by tuning the frequency of the second laser, a wide-range spectral scan is achieved, enabling high-precision measurement of gas concentration.
Drawings
To illustrate the technical solutions in the present embodiment or the prior art more clearly, the drawings needed to be used in the description of the embodiment or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
FIG. 1 is a flow chart of a method of gas concentration measurement;
FIG. 2a is a system diagram of a laser frequency locking system;
FIG. 2b is a flow chart of the laser frequency locking system to achieve laser frequency locking;
FIG. 3a is a system diagram of a laser frequency locking system;
FIG. 3b is a flow chart of the laser frequency locking system to achieve laser frequency locking;
FIG. 4 is a schematic diagram of a system for gas concentration measurement;
FIG. 5 is a schematic diagram of a system for gas concentration measurement.
Detailed Description
The method has important significance in trace gas detection on atmospheric chemical research, environmental monitoring, semiconductor production and processing and the like. The high-sensitivity laser spectrum detection technology based on the optical resonant cavity is an important means for detecting the trace gas. Under the assistance of the optical resonant cavity, the interaction length of the laser and the sample is greatly increased, and the absorption of the sample to the laser is greatly improved, so that the method has great advantages in detecting trace gas. However, when measuring gas concentration by laser absorption spectroscopy, the accuracy of the measurement results can be affected by laser parameters, including its linewidth and frequency stability.
Based on the method and the system, two paths of laser branched from a laser are processed, the first laser is subjected to laser frequency locking, the narrowing of the laser line width and the stabilization of the frequency are realized, and the second laser is tuned to realize the large-range spectrum scanning. This enables a highly accurate measurement of the gas concentration.
Fig. 1 is a flowchart of a method of gas concentration measurement, and referring to fig. 1, the method of implementing the present invention is applied to a gas concentration measurement system including: the system comprises an optical resonant cavity, a laser frequency locking system, a microwave source frequency reference scanning system and a signal acquisition and processing system. The method specifically comprises the following steps:
step 101: and filling the gas to be detected into the optical resonant cavity.
The optical resonant cavity mainly comprises two pieces of concave reflectors with ultrahigh reflectivity fixed at two ends of the cavity and a pressure measuring device.
Two opposite concave surfaces of the concave reflector form an optical resonant cavity. The concave reflector is plated with a corresponding dielectric film according to the absorption wave band of a sample to be measured. The cavity of the optical resonator is usually made of a material with a low thermal expansion coefficient to obtain a stable cavity length.
The optical resonator exhibits a plurality of longitudinal modes with equal frequency intervals in frequency, which may be referred to as Free Spectral Range (FSR), and the free spectral range has a certain correlation with the cavity length and the refractive index of the medium in the cavity under a certain cavity length, and the medium in the cavity is not substantially changed when the cavity of the optical resonator is in a sealed state or when the gas pressure inside the cavity is stable although the cavity is not in a sealed state. Therefore, the free spectral range of the optical resonant cavity is only affected by the cavity length, and the cavity length fluctuates along with the temperature change, so that the temperature of the cavity needs to be controlled in order to reduce the influence of the temperature fluctuation on the cavity length. The laser is locked on a longitudinal mode of the optical resonant cavity by a frequency locking technology, the cavity length is not changed, the frequency of the longitudinal mode is not changed, and then stable laser frequency can be obtained.
The pressure measuring device is used for measuring the pressure of the sample gas in the resonant cavity. The reason for measuring the gas pressure is that the measured spectra are different at different pressures, and pressure variations can affect the frequency-locking effect. The pressure of the gas needs to be controlled while measuring, and the specific control method comprises the following steps: in the state of flowing gas, namely in the state of filling the gas to be measured into the optical resonant cavity, the fixed extraction flow and the reading of the pressure gauge are set, and the pressure is stabilized by continuously compensating the flow of the gas inlet, wherein the pressure stabilization is understood to be dynamic stabilization.
The temperature of the cavity of the optical resonant cavity can be controlled by the following methods: the specific temperature control mode can be selected by a person skilled in the art according to the actual situation and the application scenario, and is not set herein.
When the temperature of the cavity is controlled in a position mode, the temperature can be controlled by adopting a heater, a temperature threshold value is set for the cavity, and when the real-time temperature is higher than the temperature threshold value, the heater is turned off; when the real-time temperature is higher than the temperature threshold, the heater is turned on. So that the temperature of the cavity can be dynamically balanced within a certain range.
When the cavity is controlled by adopting a cascade control mode, the temperature control can be realized by adopting a temperature control system, the temperature control system can comprise a temperature measuring module and a feedback control module, and the temperature measuring module is mainly used for monitoring the temperature of the cavity in real time and sending the measured temperature to the feedback control module. The feedback control module can set up a temperature threshold for the cavity, compare with the temperature threshold according to the real-time temperature of cavity that the temperature measurement module provided, then adjust the heating current realization of heater strip through proportional-integral control to the control of cavity temperature, so that obtain stable laser frequency, what mainly used in this application is this kind of accuse temperature mode.
When the cavity is controlled in an online non-contact control mode, the non-contact temperature control system comprises a test piece, a power supply, a heater, a light sensation temperature measurer, a silicon controlled rectifier and a data acquisition memory. A temperature control point and a target temperature are set for the chamber. The temperature control point of the cavity is sensed through the light-sensitive temperature detector, the temperature of the control point is collected, stored and analyzed, and the measurement result is compared with the target temperature; the controller is used for carrying out error analysis on the target temperature and the control point temperature, and the silicon controlled module is used for controlling the power of the heater, so that the temperature of the cavity is consistent with the target temperature; the temperature of the control point of the cavity is controlled by the light sensation temperature detector.
Step 102: and starting the laser to divide the laser into a first laser and a second laser.
The laser is a device capable of emitting laser, and can be divided into a solid laser, a gas laser, a liquid laser and a semiconductor laser according to working substances; the excitation modes can be divided into optical pump lasers, electric excitation lasers, chemical lasers and nuclear pump lasers; the operation mode can be divided into a continuous laser, a single pulse laser and the like; the range of the wave band can be divided into a far infrared laser, a mid-infrared laser and the like, the type of the applied laser is not limited in the application, and the laser can be selected by a person skilled in the art according to the actual situation and the specific application scene.
The light splitting mode of the laser can be realized by a light splitter. There are two types of beam splitters, one is a cube beam splitter and the other is a circular beam splitter. The light splitting mode of the cubic beam splitter is simple, and the cubic beam splitter has the advantage of not introducing optical path difference and optical axis deviation. The circular beam splitter has the advantages that the light splitting mode is complex, more optical lenses are needed, the energy distribution of circularly polarized light in all directions is uniform, the light splitting effect is balanced, the high-quality effect is obtained in most occasions, and the specific light splitting mode can be selected by a person skilled in the art according to actual conditions and application scenes, and is not limited herein.
Step 103: locking the frequency of the first laser with the laser frequency locking system.
The laser frequency locking system comprises a frequency modulation device, a phase detection device, a photoelectric detection device and a servo controller. The laser frequency locking steps are as follows: the frequency locking light of the laser enters the optical resonant cavity after being modulated by the spatial EOM, the light resonating with the optical resonant cavity can penetrate through the optical resonant cavity, the light with other frequencies can be reflected, the reflected light is introduced into the phase detection device to generate an error signal, the error signal is sent to the servo controller, and the current fed back to the laser by the servo controller realizes the locking of the laser frequency.
Step 104: and tuning the frequency of the second laser by using the microwave source frequency reference scanning system, and measuring to obtain a spectrum signal.
The microwave source frequency control system comprises a microwave signal generating device, a signal amplifying device, a filtering device and a laser sideband generator. The microwave signal source applies radio frequency drive to the optical fiber electro-optical crystal to generate sideband light with two frequencies on the basis of the original frequency of the laser, the frequency difference between the frequency of the sideband light and the frequency of the main laser is equal to the applied radio frequency power, so that the tuning of the second laser is realized, and the sideband laser with different frequencies generated after tuning is introduced into the optical resonant cavity to carry out spectrum detection to obtain a spectrum signal.
Step 105: and processing and analyzing the spectrum signal by using the signal acquisition and processing system to obtain the gas concentration.
The signal collecting and processing system comprises a photoelectric detector, a collecting card and a spectrum analyzer. The detection of the spectrum signal is realized by a photoelectric detector, the photoelectric detector converts the light signal into an electric signal, and then an acquisition card converts the analog voltage signal into a digital signal to be stored. And performing fitting analysis on the stored digital signal by using a spectrum analyzer so as to obtain the concentration information of the gas to be detected.
In this embodiment, the method is applied to a gas concentration measurement system comprising: the system comprises an optical resonant cavity, a laser frequency locking system, a microwave source frequency reference scanning system and a signal acquisition and processing system. The specific measurement method comprises the following steps: and filling the gas to be detected into the optical resonant cavity, controlling the pressure of the gas, starting the laser, and dividing the laser into a first laser and a second laser.
And then, locking the frequency of the first laser by a laser frequency locking system, tuning the frequency of the second laser by a microwave source frequency reference scanning system to realize large-range spectrum scanning, and obtaining a spectrum signal. And finally, processing and analyzing the spectrum signal through a signal acquisition and processing system to obtain the gas concentration. Therefore, the frequency is locked by one path of laser to realize the frequency stability, and the frequency is tuned by the other path of laser to realize the scanning of a spectrum signal in a large range, thereby finally realizing the high-precision measurement of the gas concentration.
The order of the steps is merely for convenience of description, and is not limited to the technical solution of the present application, and in practical applications, other implementation orders may be adopted, for example, the order of the steps 101 and 102 is exchanged.
Fig. 2a is a system diagram of a laser frequency locking system, as shown in fig. 2a, the laser frequency locking system includes: frequency modulation device, phase detection device, photoelectric detection device and servo controller. Fig. 2b is a flow chart of the laser frequency locking system to achieve laser frequency locking. As shown in fig. 2b, step 103 in the method provided in the foregoing embodiment may be implemented by the following steps:
step 201: modulating the frequency of the first laser light output by the laser.
This step can be implemented by using a frequency modulation device, and the phase of the reflected light needs to be obtained in the process of frequency locking the laser, because the phase contains frequency information. In obtaining the phase of the reflected light, phase modulation is typically applied to the laser, with a well-defined phase relationship between the sideband produced by the modulation and the frequency of the reflected light, although they are different. If these sidebands interfere with the reflected light, the phase of the beat frequency can be measured and the phase of the reflected light can be derived from the beat frequency phase. Thereby locking the frequency of the laser by an error signal generated by the phase change on both sides of the formant.
The phase modulation can adopt electro-optic phase modulation which can be divided into inner modulation and outer modulation. The inner modulation means: during the laser forming process, a certain parameter of laser oscillation is changed according to the rule of a modulation signal. I.e. the formation of the laser is controlled by a modulation signal. External modulation refers to placing the modulator outside the laser where the modulator is independent of the laser formation. The selection of the modulation method can be performed by those skilled in the art according to actual situations and specific scenarios, and is not limited herein.
Step 202: and converting the first laser light into an electric signal from an optical signal.
This step can be implemented by using a photoelectric detection device, and usually, the optical signal is processed by converting it into an electrical signal and a radio frequency signal which are easy to process, and the photoelectric detection device is used for converting the laser signal generated by the laser method into an electrical signal.
Step 203: the electrical signal is demodulated to obtain an error signal.
Demodulation can be accomplished using a phase detection device. Modulation is the process of using baseband signals to control the variation of one or more parameters of a carrier signal and load information thereon to form a modulated signal for transmission, while demodulation is the inverse process of modulation, and the original baseband signal is recovered from the parameter variation of the modulated signal by a specific method. The phase of the reflected light can be obtained by modulation and demodulation so that there is a positive and negative difference around the resonance frequency for use as an error signal.
The error signal actually means a deviation between an actual value and a set value, and is compensated by PID (proportional, integral, derivative) feedback control when the deviation is not zero. If the laser frequency is consistent with the resonance frequency of the optical cavity, the demodulation signal is 0, the error signal does not exist, when the laser frequency is higher than the resonance frequency of the optical resonant cavity, the demodulation signal is positive, and when the laser frequency is lower than the resonance frequency of the optical resonant cavity, the demodulation signal is negative and can be used as the error signal.
Step 204: and converting the error signal into a signal which is fed back to the laser and controls the frequency of the first laser output by the laser.
An error signal is obtained after phase demodulation, and then the error signal is processed by a low-pass filter and a PID (proportional integral circuit) and fed back to other response devices such as piezoelectric ceramics of a laser or an acousto-optic modulator for frequency compensation.
In this embodiment, laser is output by a laser, and then passes through an EOM crystal (electro-optical modulator) electro-optical modulator to perform radio-frequency electro-optical phase modulation on an optical field of the laser, and then a modulated laser signal enters an optical resonant cavity, resonates with the optical resonant cavity, and is reflected to a photodetector. The phase detection device is used for carrying out phase demodulation on the reflected light signal to obtain frequency detuning information in the reflected light, an error signal is generated, then the frequency detuning information is processed by a proportional-integral circuit, a frequency error signal between the laser and the optical resonant cavity used as a reference is obtained through photoelectric detection, and the laser frequency is compensated in real time to be locked on the resonant frequency of the reference cavity. Therefore, the stability of the laser frequency is ensured, the reference of the laser frequency relative to the optical cavity mode frequency is realized, and the measurement precision is improved.
Fig. 3a is a system schematic diagram of a laser frequency locking system, and as shown in fig. 3a, the microwave source frequency control system comprises a microwave signal generating device, a signal amplifying device, a filtering device and a laser sideband generator.
Fig. 3b is a flow chart of the laser frequency locking system to achieve laser frequency locking. As shown in fig. 3b, step 104 in the method provided in the foregoing embodiment can be implemented by the following steps:
step 301: and generating microwave signals with different frequencies by using the second laser.
This step may be achieved by a microwave signal generating means. The purpose of generating microwave signals at different frequencies is that the spectral measurement requires light at different frequencies, which frequencies are obtained by means of the microwave signals.
Step 302: and carrying out power amplification on the microwave signal.
The power of the sideband laser is related to the intensity of the radio frequency signal, and the sideband power generated by the microwave source is limited, so that a signal amplifier is required to amplify the power of the microwave signal generated by the microwave signal generator.
Step 303: and filtering the high-order signals in the amplified microwave signals to obtain filtered microwave signals.
This step may be implemented by filtering means. The purpose of filtering out high-order signals is that high-frequency signals may be coupled into the optical resonant cavity, which affects the accuracy of the spectral measurement.
Step 304: sideband lasers with different frequencies are generated by utilizing the filtered microwave signals and are introduced into the optical resonant cavity for spectrum detection.
The microwave signal source applies radio frequency drive to the optical fiber electro-optical crystal to generate sideband light with two frequencies on the basis of the original frequency of laser, and the frequency difference between the frequency of the sideband light and the frequency of the main laser is equal to the applied radio frequency power.
Each time the sideband laser light is introduced into the optical cavity is of a specific frequency, since spectral detection requires that the specific absorption coefficient at each frequency be known, it is necessary to measure one frequency at a time and finally integrate the absorption coefficients at these frequencies to obtain an absorption spectrum. The spectral measurement is to record the absorption coefficients of substances under different frequencies, and the horizontal axis of the obtained spectrum is the laser frequency and the vertical axis is the absorption coefficient. The optical resonant cavity is subjected to spectrum detection through sideband lasers with different frequencies, so that the detection light can be matched with any longitudinal mode of the optical cavity, the large-range spectrum scanning is realized, the larger the spectrum scanning range is, the larger the corresponding measurement range is, and the final measurement result is more accurate.
In this embodiment, different microwave signals are generated by using the second laser, power amplification and high-order signal filtering are performed on the microwave signals, after the filtered microwave signals pass through the electro-optical modulation crystal, light (sideband light) with two frequencies is additionally generated on the basis of the original laser frequency (main laser) by applying an electric field and radio frequency drive to the crystal, the light enters the optical resonant cavity through different sideband lasers to perform spectrum detection, and the detection light can be matched with any longitudinal mode of the optical resonant cavity, so that spectrum scanning in a large range is realized, and high-precision measurement of gas concentration is realized.
Although the operations are depicted in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order. Under certain circumstances, multitasking and parallel processing may be advantageous.
It should be understood that the various steps recited in the method embodiments of the present application may be performed in a different order and/or in parallel. Moreover, method embodiments may include additional steps and/or omit performing the illustrated steps. The scope of the present application is not limited in this respect.
Fig. 4 is a schematic structural diagram of a system for measuring a gas concentration, and as shown in fig. 4, the present invention further provides a system for measuring a gas concentration, including:
an optical resonant cavity 100, a laser 200, a laser frequency locking system 300, a microwave source frequency reference scanning system 400, and a signal acquisition and processing system 500;
the optical resonant cavity 100 is used for receiving a gas to be measured;
the laser 200 is used for emitting laser and dividing the laser into a first laser and a second laser;
the laser frequency locking system 300 is used for locking the frequency of the first laser;
the microwave source frequency reference scanning system 400 is configured to tune the frequency of the second laser and measure the frequency to obtain a spectrum signal;
the signal acquisition and processing system 500 is used to process and analyze the spectral signals to obtain gas concentrations.
The laser frequency locking system 300 includes: a frequency modulation device 301, a phase detection device 302, a photoelectric detection device 303 and a servo controller 304. The frequency modulation device 301 is used for modulating the frequency of the first laser output by the laser; the photoelectric detection device 303 is used for converting the first laser light from an optical signal to an electrical signal; a phase detection device 302 for demodulating the electrical signal to obtain an error signal; the servo controller 304 is configured to convert the error signal into a signal that is fed back to the laser and controls the frequency of the first laser output by the laser.
The microwave source frequency reference scanning system 400 includes: a microwave signal generating device 401, a signal amplifying device 402, a filtering device 403 and a laser sideband generator 404. The microwave signal generating device 401 is configured to generate microwave signals with different frequencies by using the second laser; the signal amplifying device 402 is configured to amplify and output the microwave signal; the filtering device 403 is configured to filter the high-order signal output by the signal amplifying device; the laser sideband generator 404 is used for generating sideband laser light with different frequencies through the microwave signal and introducing the sideband laser light into the optical resonant cavity for spectrum detection.
The system further includes a pressure measuring device 600, the pressure measuring device 600 is used for measuring the pressure of the gas to be measured in the optical resonant cavity, and specifically includes: and under the state that the gas to be measured is filled, the fixed air exhaust flow and the reading of the pressure gauge are set, and the pressure is stabilized by continuously compensating the flow of the gas to be measured at the air inlet of the optical resonant cavity.
The system further includes a temperature control system 700, where the temperature control system 700 is configured to control the temperature of the optical resonant cavity, and specifically includes: a temperature point is set for the optical resonant cavity, and then the heating current of the heating wire is adjusted through proportional-integral control to realize the control of the temperature point.
In this embodiment, the laser 200 generates a first laser and a second laser, wherein the first laser enters the laser frequency locking system 300, the laser frequency locking system 300 locks the frequency of the first laser on the longitudinal mode of the optical resonator, and the high precision of the cavity is utilized to realize the narrowing of the laser linewidth and the stabilization of the frequency. The second laser enters the microwave source frequency reference scanning system 400, the frequency of the second laser is tuned to other longitudinal modes of the optical resonant cavity by the microwave source frequency reference scanning system 400, and the second laser is used for detecting the spectrum signal. Finally, the signal acquisition and processing system 500 fits the spectrum signal detected by the second laser and calculates the data to obtain the concentration of the gas to be measured.
By the gas concentration measuring system, high-precision measurement of the gas concentration can be realized.
Fig. 5 is a schematic diagram of a gas concentration measurement system, and as shown in fig. 5, the working principle of the system specifically includes: after light is emitted from the laser 100, the light is divided into two beams after passing through the beam splitter 200, the first laser generated by the beam splitter 200 is frequency-locked light and enters the optical resonant cavity after passing through the reflector, and because a signal of reflected light is used in PDH, the light reflected back from the cavity mirror is introduced into the detector 300 through the prism. The signal in the detector is finally fed back to the laser 100 through the frequency locking system 400, so as to realize the locking of the laser frequency. The second laser light generated by the beam splitter 200 is used as a detection laser for measuring the absorption coefficient of the absorption medium. The second laser light passes through the laser sideband generator 500 to generate laser light at different frequencies, which are generated by the microwave source. The reason for using two lasers to enter the optical cavity here is that the frequency of the laser is first locked to the longitudinal mode of the optical cavity by the frequency-locked laser, i.e. the first laser, and the laser frequency is stable at this time. Whereas a scanned spectrum requires absorption at different laser frequencies. This requires that the detection laser, i.e., the second laser, be introduced into the laser sideband modulator 600, controlled by the microwave source control system 700, to generate sideband lasers at different frequencies for spectral detection. Besides, the temperature control system 800 controls the temperature of the optical resonant cavity 100, and the signal acquisition and processing system 900 acquires and processes the spectral signals to obtain the concentration of the gas to be measured.
Computer program code for carrying out operations for aspects of the present invention may be written in any combination of one or more programming languages, including an object oriented programming language such as Java, smalltalk, C + + or the like and conventional procedural programming languages, such as the "C" programming language or similar programming languages. The program code may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user's computer through any type of network, including a Local Area Network (LAN) or a Wide Area Network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet service provider).
It is further noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising a … …" does not exclude the presence of another identical element in a process, method, article, or apparatus that comprises the element.
Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.
While several specific implementation details are included in the above discussion, these should not be construed as limitations on the scope of the disclosure. Certain features that are described in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination.
The above description is only one specific embodiment of the present application, but the scope of the present application is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present application should be covered by the scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.
Claims (10)
1. A method of gas concentration measurement, wherein the method is applied to a gas concentration measurement system comprising: an optical resonator, a laser frequency locking system, a microwave source frequency reference scanning system, and a signal acquisition and processing system, the method comprising:
filling gas to be detected into the optical resonant cavity;
starting a laser, and dividing the laser into a first laser and a second laser;
locking the frequency of the first laser with the laser frequency locking system;
tuning the frequency of the second laser by using the microwave source frequency reference scanning system, and measuring to obtain a spectrum signal;
and processing and analyzing the spectrum signal by using the signal acquisition and processing system to obtain the gas concentration.
2. The method of claim 1, wherein the tuning the frequency of the second laser using the microwave source frequency reference scanning system and measuring a resulting spectral signal comprises:
generating microwave signals with different frequencies by using the second laser;
performing power amplification on the microwave signal;
filtering out a high-order signal in the amplified microwave signal to obtain a filtered microwave signal;
sideband lasers with different frequencies are generated by the filtered microwave signals and are introduced into the optical resonant cavity for spectrum detection.
3. The method according to claim 1, wherein said locking the frequency of the first laser with the laser frequency locking system comprises:
modulating the frequency of the first laser light output by the laser;
converting the first laser light from an optical signal to an electrical signal;
demodulating the electrical signal to obtain an error signal;
and converting the error signal into a control signal and feeding the control signal back to the laser, wherein the control signal is used for controlling the frequency of the first laser output by the laser.
4. The method of claim 1, wherein prior to activating the laser, the method further comprises:
and setting a fixed pumping flow rate in the state that the gas to be measured is filled, and adjusting the flow rate of the gas to be measured at the gas inlet of the optical resonant cavity so as to maintain the pressure in the optical resonant cavity at a preset pressure value.
5. The method of claim 1, wherein the gas concentration measurement system further comprises a temperature control system, the temperature control system comprising a heating wire, and wherein the method further comprises, prior to filling the optical cavity with the gas to be measured:
starting the temperature control system to control the temperature of the optical resonant cavity;
and adjusting the heating current of the heating wire through proportional-integral control in the temperature control system so as to maintain the temperature in the optical resonant cavity at a preset temperature.
6. The method of claim 1, wherein the processing and analyzing the spectrum signal by using a signal acquisition and processing system to obtain the gas concentration comprises:
converting the spectral signal into a voltage signal;
converting the voltage signal into a digital signal and converting the digital signal;
determining the gas concentration from the digital signal.
7. A system for gas concentration measurement, the system comprising: the system comprises an optical resonant cavity, a laser frequency locking system, a microwave source frequency reference scanning system and a signal acquisition and processing system;
the optical resonant cavity is used for receiving gas to be detected;
the laser is used for emitting laser and dividing the laser into a first laser and a second laser;
the laser frequency locking system is used for locking the frequency of the first laser;
the microwave source frequency reference scanning system is used for tuning the frequency of the second laser and measuring to obtain a spectrum signal;
the signal acquisition and processing system is used for processing and analyzing the spectrum signal to obtain the gas concentration.
8. The system of claim 7, wherein the microwave source frequency reference scanning system is specifically configured to:
the device comprises a microwave signal generating device, a signal amplifying device, a filtering device and a laser sideband generator;
the microwave signal generating device is used for generating microwave signals with different frequencies by using the second laser;
the signal amplification device is used for performing power amplification on the microwave signal and outputting the microwave signal;
the filtering device is used for filtering the high-order signal output by the signal amplifying device;
the laser sideband generator is used for generating sideband laser with different frequencies through the microwave signal and introducing the sideband laser into the optical resonant cavity for spectrum detection.
9. The system according to claim 7, further comprising a pressure measuring device, wherein the pressure measuring device is configured to measure the pressure of the gas to be tested in the optical resonant cavity, and to adjust the flow rate of the gas to be tested at the gas inlet of the optical resonant cavity according to the set fixed pumping flow rate in the state that the gas to be tested is filled, so as to maintain the pressure in the optical resonant cavity at a preset pressure value.
10. The system of claim 7, further comprising a temperature control system comprising a heating wire, the temperature control system configured to adjust a heating current of the heating wire by proportional-integral control to maintain a temperature within the optical cavity at a preset temperature.
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