Disclosure of Invention
The inventor provides a ring-down cavity longitudinal mode matching method and a ring-down cavity longitudinal mode matching system aiming at the problems and the technical requirements, and the technical scheme of the invention is as follows:
a ring-down cavity longitudinal mode matching method comprises the steps of providing a CRDS platform and a light detector, wherein the CRDS platform comprises a ring-down cavity and a laser used for generating detection laser, and the detection laser is incident into the ring-down cavity;
When the ring-down cavity longitudinal mode matching is carried out, the working parameters of the laser are adjusted to enable the frequency of the detection laser to fluctuate within the frequency fluctuation range, the light detector is used for detecting the light beam in the ring-down cavity and generating an optical detection electric signal, and the frequency fluctuation range of the detection laser is adjusted according to the optical detection electric signal generated by the light detector until the detection laser and the ring-down cavity form single longitudinal mode matching within the frequency fluctuation range.
The further technical scheme is that the working parameters of the laser are regulated through periodic signal waves, and the signal waves are generated by a signal wave generator;
When the ring-down cavity longitudinal modes are matched, the optical detection electric signals generated by the optical detector are transmitted into the signal wave generator, and the signal wave generator adjusts the amplitude of the signal wave according to the optical detection electric signals so as to adjust the frequency fluctuation range of the detection laser.
The further technical scheme is that when the amplitude of the periodic signal wave is regulated according to the optical detection electric signal, the method comprises the following steps:
Confirming the number of times of longitudinal mode matching of detection laser and a ring-down cavity in one period of a signal wave according to the optical detection electric signal, and acquiring the number of mismatching times n of the detection laser and the ring-down cavity based on the number of times of longitudinal mode matching of the detection laser and the ring-down cavity in one period of the signal wave and the target matching times;
When the number of mismatching times n is more than k1, the amplitude of the signal wave is regulated by a first step length, wherein k1 is a matching threshold value;
And when the number of mismatching times n is less than or equal to k1, adjusting the amplitude of the signal wave by a second step length, wherein the second step length is smaller than the first step length.
The working parameters of the laser comprise working current or working voltage;
When the working parameters of the laser are working currents, the working parameters of the laser are adjusted through periodic signal waves, wherein the working parameters comprise signal wave current formed based on signal waveforms, and the signal wave current is superposed in the original driving current of the laser, so that the working current of the laser is adjusted based on the superposed signal wave current.
The further technical scheme is that when the detection laser and the ring-down cavity form single longitudinal mode matching, the frequency fluctuation range of the detection laser is smaller than the FSR of the ring-down cavity.
The periodic signal wave comprises a triangular wave.
A ring-down cavity longitudinal mode matching system for implementing the ring-down cavity longitudinal mode matching method, wherein the ring-down cavity longitudinal mode matching system comprises a light detector connected with a CRDS platform, the CRDS platform comprises a ring-down cavity and a laser for generating detection laser, and the detection laser is incident into the ring-down cavity;
When the ring-down cavity longitudinal mode matching is carried out, the working parameters of the laser are adjusted to enable the frequency of the detection laser to fluctuate within the initial frequency fluctuation range, the light detector is used for detecting the light beam in the ring-down cavity and generating an optical detection electric signal, and the frequency fluctuation range of the detection laser is adjusted according to the optical detection electric signal generated by the light detector until the detection laser and the ring-down cavity form single longitudinal mode matching within the frequency fluctuation range.
The further technical scheme is that the device comprises a power supply module, a signal wave generator and a driving module;
The power supply module is connected with the signal wave generator and the driving module and is used for supplying power to the signal wave generator and the driving module;
The signal wave generator is connected with the driving module and the optical detector, the driving module is connected with the laser, the signal wave generator generates signal wave voltage according to the optical detection electric signal and inputs the signal wave voltage into the driving module, and the driving module converts the signal wave voltage into signal wave current and inputs the signal wave current into the laser.
The signal wave generator comprises a matching detection unit, a main control unit, a parameter adjusting unit and an output unit which are connected in an adapting way;
The matching detection unit is used for receiving the optical detection electric signal generated by the optical detector and judging the mismatching times n of the detection laser and the ring-down cavity according to the optical detection electric signal;
The main control unit is used for comparing the relation between the number of mismatching times n and the matching threshold k1, the parameter adjusting unit is used for adjusting the amplitude of the signal wave voltage according to the relation between the number of mismatching times n and the matching threshold k1, and the output unit is used for outputting the signal wave voltage to the driving module.
The further technical scheme is that the system further comprises an interaction module, and the interaction module is connected with the signal wave generator through a communication interface.
The beneficial technical effects of the invention are as follows:
When the ring-down cavity longitudinal mode matching is carried out, the working parameters of the laser are actively regulated to enable the frequency of the detection laser to generate fluctuation, and the frequency fluctuation range of the detection laser is regulated according to the optical detection electric signal generated by the optical detector until the detection laser and the ring-down cavity form single longitudinal mode matching in the frequency fluctuation range. According to the invention, single longitudinal mode matching is realized between the detection laser and the ring-down cavity in the process of frequency dynamic change, the adjustment difficulty of the detection laser is reduced, the adjustment speed of the longitudinal mode matching of the ring-down cavity is improved, and the situation that the detection laser and the ring-down cavity are subjected to multi-longitudinal mode matching is avoided, so that the measurement precision and the response speed of the CRDS platform are improved.
Detailed Description
The following describes the embodiments of the present invention further with reference to the drawings.
In order to solve the problems of low ring-down cavity longitudinal mode matching efficiency and poor matching stability, the invention provides a ring-down cavity longitudinal mode matching method, and in one embodiment of the invention, the ring-down cavity longitudinal mode matching method comprises the following steps:
Providing a CRDS platform and a light detector, wherein the CRDS platform comprises a ring-down cavity 7 and a laser 6 for generating detection laser, and the detection laser is incident into the ring-down cavity 7;
When the ring-down cavity longitudinal mode matching is carried out, the working parameters of the laser 6 are adjusted to enable the frequency of the detection laser to fluctuate within an initial frequency fluctuation range, after the detection laser is incident into the ring-down cavity 7, the light detector is used for detecting the light beam in the ring-down cavity 7 and generating an optical detection electric signal, and the frequency fluctuation range of the detection laser is adjusted according to the optical detection electric signal generated by the light detector until the detection laser and the ring-down cavity 7 form single longitudinal mode matching within the frequency fluctuation range.
Specifically, the CRDS platform, i.e., a platform for detecting trace gases using cavity ring-down spectroscopy, generally includes a ring-down cavity 7 and a laser 6, the laser 6 being configured to generate a detection laser incident within the ring-down cavity 7. In practice, the ring-down cavity 7 and the laser 6 may take the forms commonly used in the art, and the detection laser generated by the laser 6 is generally transmitted into the ring-down cavity 7 through an optical fiber 8. In particular, since DFB (Distributed Feedback Laser) lasers have a wide frequency tuning range and good frequency tunability, DFB lasers are preferred for the laser 6 in this embodiment.
As known from the background art, in the CRDS technology, the precondition for the ring-down event is that the detection laser and the ring-down cavity achieve good longitudinal mode matching, and a plurality of longitudinal modes exist in the ring-down cavity 7, and the detection laser is matched with only one longitudinal mode, namely single longitudinal mode matching. In the prior art, the frequency of the detection laser is difficult to be fixed at a stable value, namely, the frequency of the detection laser can generate irregular oscillation, in the oscillation process of the frequency of the detection laser, the situation that the detection laser is matched with a plurality of longitudinal modes of the ring-down cavity 7 in sequence often occurs, namely, the situation that the detection laser is matched with a plurality of longitudinal modes of the ring-down cavity 7, and the mode noise is generated by the multi-longitudinal mode matching, so that the measurement precision of the CRDS platform is reduced.
In order to solve the above-mentioned problems, in this embodiment, when the ring-down cavity longitudinal mode matching is performed, the working parameters of the laser 6 are actively adjusted to make the frequency of the detection laser fluctuate, and the condition of the longitudinal mode matching between the detection laser and the ring-down cavity 7 is judged according to the optical detection electric signal generated by the optical detector, and then the frequency fluctuation range of the detection laser is continuously adjusted according to the condition of the longitudinal mode matching until the detection laser and the ring-down cavity 7 form single longitudinal mode matching within the frequency fluctuation range. In this case, the frequency of the detection laser light coincides with only one of the longitudinal mode frequencies v in the frequency fluctuation range of the detection laser light. After the frequency fluctuation range of the detection laser is adjusted, the frequency of the detection laser continuously fluctuates in the frequency fluctuation range so as to coincide with the same longitudinal mode frequency v for multiple times in the fluctuation process, and multiple times of single longitudinal mode matching is formed.
When the detection laser and the ring-down cavity 7 form longitudinal mode matching, light energy accumulation can occur in the cavity, at the moment, the light detection electric signal generated by the light detector can be enhanced drastically, so that whether the detection laser and the ring-down cavity 7 are longitudinally mode matched can be judged according to the intensity change of the light detection electric signal detected by the light detector. In this embodiment, when the intensity of the optical detection electrical signal is greater than the signal threshold, it is determined that the detection laser and the ring-down cavity 7 form a primary longitudinal mode match, where the signal threshold may be set according to the detection requirement of the gas to be detected. By combining the fluctuation state of the detection laser and the number of times of the detection laser and the ring-down cavity 7 forming the longitudinal mode matching, whether the detection laser and the ring-down cavity 7 form the single longitudinal mode matching in the frequency fluctuation range can be judged, and the specific judgment mode for forming the single longitudinal mode matching in the embodiment can be referred to as the following description.
In practice, other technical means may be used to determine whether the detection laser forms a single longitudinal mode match with ring down cavity 7. The photodetector is typically formed by a photodiode, a signal amplifying circuit, and a signal filtering circuit that are adapted to convert an optical signal into an optical detection electrical signal and amplify the optical detection electrical signal. In specific implementation, the optical detector may take a conventional form, and the manner of detecting the light beam in the ring-down cavity 7 by using the optical detector may also be consistent with the prior art, which is not described herein.
When the ring-down cavity longitudinal mode matching is carried out, the working parameters of the laser 6 are actively regulated to enable the frequency of the detection laser to generate fluctuation, and the frequency fluctuation range of the detection laser is regulated according to the optical detection electric signal generated by the optical detector until the detection laser and the ring-down cavity 7 form single longitudinal mode matching in the frequency fluctuation range. According to the invention, single longitudinal mode matching is realized between the detection laser and the ring-down cavity 7 in the process of frequency dynamic change, the adjustment difficulty of the detection laser is reduced, the adjustment speed of the longitudinal mode matching of the ring-down cavity is improved, and the situation that the detection laser is matched with the ring-down cavity 7 in multiple longitudinal modes is avoided, so that the measurement precision and the response speed of the CRDS platform are improved.
Preferably, to further increase the frequency of the single longitudinal mode match, when the detection laser and ring down cavity 7 form a single longitudinal mode match, the frequency fluctuation range of the detection laser is smaller than the FSR (FREE SPECTRAL RANGE ) of the ring down cavity 7, and it is understood that the frequency fluctuation range of the detection laser is smaller than the FSR of the ring down cavity 7, meaning that the difference between the maximum and minimum values of the frequency of the detection laser during the fluctuation is smaller than the FSR of the ring down cavity 7. The FSR represents the adjacent longitudinal mode frequency interval Δv, fsr=Δv=c/2 nL, where c is the speed of light, n is the refractive index of the gas, and L is the cavity length of the ring-down cavity 7. For a ring-down chamber 7 containing a gas to be measured, the chamber length L of the ring-down chamber 7 and the gas refractive index n can be determined, and at this time, the FSR of the ring-down chamber 7 can be determined by the above method, and the FSR is a constant value.
Further, the operating parameters of the laser 6 are adjusted by means of a periodic signal wave, which is generated by the signal wave generator 4;
When the ring-down cavity longitudinal mode matching is carried out, the optical detection electric signal generated by the optical detector is transmitted into the signal wave generator 4, and the signal wave generator 4 adjusts the amplitude of the signal wave according to the optical detection electric signal so as to adjust the frequency fluctuation range of the detection laser.
Specifically, to ensure the frequency of single longitudinal mode matching, the working parameters of the laser 6 are adjusted by using a periodic signal wave, so that after the adjustment of the frequency fluctuation range of the detection laser is completed, the detection laser periodically forms single longitudinal mode matching with the ring-down cavity 7 in the frequency fluctuation range. Preferably, the signal wave is a triangular wave, and since the change rate of the triangular wave when the instantaneous value rises or falls is kept unchanged, the change rate of the detected laser frequency when rising or falling is also kept unchanged by the adjustment of the triangular wave, so when longitudinal mode matching occurs at any moment of the rise or fall of the detected laser frequency, that is, when the detected laser frequency is coincident with the longitudinal mode frequency v, the time for forming light energy accumulation in the ring-down cavity 7 is fixed, and the intensity of the optical detection electric signal detected and generated by the optical detector is the same when the longitudinal mode matching is performed, so that the condition of judging the longitudinal mode matching according to the intensity change of the optical detection electric signal is facilitated. In specific implementation, the type of the signal wave can be selected according to actual requirements, for example, the signal wave can be a sine wave, and the like, and the detection of the fluctuation of the laser frequency can be adjusted.
In this embodiment, in order to improve the efficiency of adjusting the frequency of the detection laser, in implementation, the initial amplitude of the triangular wave is set relatively larger, so that the frequency of the detection laser fluctuates in a larger initial frequency fluctuation range, and in the ring-down cavity longitudinal mode matching process, the amplitude of the triangular wave is gradually reduced, so that the frequency fluctuation range of the detection laser is gradually reduced, until the detection laser and the ring-down cavity form single longitudinal mode matching in the frequency fluctuation range. When the initial frequency fluctuation range, that is, the triangular wave amplitude is the initial amplitude, the fluctuation range of the laser frequency under the adjustment of the triangular wave is detected, and generally, the initial frequency fluctuation range can be set according to actual requirements.
As is clear from the above description, in this embodiment, by combining the fluctuation state of the detection laser and the number of times of the detection laser forming the longitudinal mode matching with the ring down cavity 7, it is determined whether the detection laser forms the single longitudinal mode matching with the ring down cavity 7 in the frequency fluctuation range, specifically, the target matching number of times of the detection laser and the ring down cavity 7 is determined by detecting the fluctuation state of the laser, and when the number of times of the longitudinal mode matching in one period of the signal wave is equal to the target matching number of times, it is determined that the detection laser forms the single longitudinal mode matching with the ring down cavity 7 in the frequency fluctuation range.
The target matching times refer to corresponding longitudinal mode matching times in one period of the signal wave when single longitudinal mode matching is realized under the adjustment of the current signal wave type. In this embodiment, the signal wave is a triangular wave, and under the adjustment of the triangular wave, the working parameter of the laser 6 changes along with the instantaneous value of the triangular wave in one period of the triangular wave, so that the frequency of the detection laser generated by the laser 6 rises and falls in one period of the triangular wave, and the detection laser frequency at each moment in the rising edge is equal to the detection laser frequency at each moment in the falling edge in a one-to-one correspondence. When the detection laser realizes single longitudinal mode matching under the regulation of the triangular wave, the frequency of the detection laser only coincides once with the longitudinal mode frequency v at the frequency peak value in one period of the triangular wave, or the frequency of the detection laser coincides once with the longitudinal mode frequency v at a certain moment of the rising edge and at the corresponding moment of the falling edge respectively, namely, when the single longitudinal mode matching is realized under the regulation of the triangular wave, the corresponding longitudinal mode matching times in one period of the signal wave are 1 or 2 times. However, since the frequency of the detection laser only coincides with the longitudinal mode frequency v at a frequency peak value, and since the fluctuation range of the detection laser frequency is changed from large to small when the detection laser frequency is adjusted in this embodiment, and the step length of the change of the frequency fluctuation range is generally much smaller than the FSR of the ring-down cavity 7, when the detection laser and the ring-down cavity 7 form single longitudinal mode matching, the situation that the frequency of the detection laser coincides with the longitudinal mode frequency v once at a certain time of the rising edge and at a corresponding time of the falling edge will occur only at the frequency peak value and the longitudinal mode frequency v before the situation that the frequency of the detection laser coincides with the longitudinal mode frequency v. Therefore, in this embodiment, when the detection laser forms 2 longitudinal mode matches with the ring-down cavity 7 in one period of the triangular wave, it represents that the detection laser has formed a single longitudinal mode match with the ring-down cavity 7, that is, the target matching number is 2 in this embodiment.
Further, the operating parameters of the laser 6 include an operating current or an operating voltage;
When the working parameter of the laser 6 is working current, the step of adjusting the working parameter of the laser 6 through the periodic signal wave includes forming a signal wave current based on the signal wave, and superposing the signal wave current in the original driving current of the laser 6 so as to adjust the working current of the laser 6 based on the superposed signal wave current.
Specifically, the working parameters of the laser 6 include a working current or a working voltage, the modulation type of the laser 6 may be a current modulation type or a voltage modulation type, and correspondingly, when the laser 6 is of a current modulation type, the adjusted working parameters are the working current of the laser 6; when the laser 6 is voltage modulation type, the adjusted working parameter is the working voltage of the laser 6.
In this embodiment, the laser 6 is a current modulation type, when the working current of the laser 6 is adjusted by the periodic signal wave, the signal wave current is superimposed in the original driving current of the laser 6, so as to adjust the working current of the laser 6 based on the superimposed signal wave current, that is, the working current of the laser 6 is the sum of the signal wave current and the original driving current, and the working current of the laser 6 is changed due to the change of the signal wave current.
As is known to those skilled in the art, with respect to the current modulation type laser 6, the frequency of the detection laser light generated by the laser 6 can be controlled by configuring the operation current of the laser 6, and thus, the present embodiment configures the operation current of the laser 6 by the signal wave current, thereby controlling the frequency of the detection laser light generated by the laser 6. In this case, the amplitude of the signal wave is specifically the amplitude of the signal wave current, and the signal wave is generally a waveform formed by the change of the signal wave voltage with time, and the signal wave current is generally converted from the signal wave voltage, so that the amplitude of the signal wave current is generally adjusted by adjusting the voltage amplitude of the signal wave. In this embodiment, the signal wave is a triangular wave, and the signal wave current is superimposed on the primary driving current of the laser 6, that is, the triangular wave current is superimposed on the primary driving current of the laser 6, and generally, the variation range of the triangular wave current value is 0-10mA. The conversion mode of correspondingly converting the signal wave voltage into the signal wave current can be the existing common mode.
Further, when the amplitude of the signal wave is regulated according to the optical detection electric signal, the method comprises the steps of obtaining the mismatching times n of the detection laser and the ring-down cavity based on the times of longitudinal mode matching and target matching times of the detection laser and the ring-down cavity in one period of the signal wave;
When the number of mismatching times n is more than k1, the amplitude of the signal wave is regulated by a first step length, wherein k1 is a matching threshold value;
And when the number of mismatching times n is less than or equal to k1, adjusting the amplitude of the signal wave by a second step length, wherein the second step length is smaller than the first step length.
Specifically, the number of mismatching n refers to the number of longitudinal mode matching exceeding the target number of matching in one period of the signal wave, that is, the number of mismatching n is the difference between the number of longitudinal mode matching in one period of the signal wave and the target number of matching. The step of judging the number of mismatching times n of the detection laser and the ring-down cavity 7 according to the optical detection electric signal specifically means that the number of times that the intensity of the optical detection electric signal detected by the optical detector is larger than a signal threshold value is recorded in one period of the signal wave so as to obtain the number of longitudinal mode matching times in one period of the signal wave, and the number of longitudinal mode matching times is subtracted from the number of target matching times and an absolute value is taken, so that the number of mismatching times n of the detection laser and the ring-down cavity 7 can be obtained.
As can be seen from the above description, in this embodiment, the signal wave is a triangular wave, and in the ring-down cavity longitudinal mode matching process, the amplitude of the triangular wave current is adjusted to change the frequency fluctuation range of the detection laser from large to small, specifically, when the amplitude of the triangular wave current is large, the frequency fluctuation range of the detection laser is also large, the detection laser will overlap with a plurality of longitudinal mode frequencies v in one period of the triangular wave, the number of mismatching times is large, at this time, the amplitude of the triangular wave current is reduced by adopting a larger first step size, and coarse adjustment is performed on the frequency fluctuation range of the detection laser, so as to improve the efficiency of longitudinal mode matching adjustment.
Along with the gradual reduction of the amplitude of the triangular wave current, the frequency fluctuation range of the detection laser is also gradually reduced, at this time, the longitudinal mode matching times of the detection laser in one period of the triangular wave gradually approach to the target matching times, namely the mismatching times n gradually approach to zero, when the mismatching times n is less than or equal to a matching threshold k1, the amplitude of the triangular wave current is continuously reduced by using a smaller second step length, so that the frequency fluctuation range of the detection laser is finely adjusted until the mismatching times n=0, namely the detection laser and the ring-down cavity 7 form single longitudinal mode matching.
In this embodiment, in the process of matching the threshold k1=2 and adjusting the amplitude of the triangular wave current, the first step may be 1mA, and the second step may be 0.5mA. Fig. 3 shows a schematic diagram of amplitude adjustment of the triangular wave current in this embodiment, as shown in fig. 3, the initial amplitude of the triangular wave current is 10mA, the initial frequency is 10Hz, the number of mismatching times n is greater than 2 within 0-0.6s, and the amplitude of the triangular wave current is reduced by a first step size of 1 mA. In 0.6-1.1s, the mismatching frequency n is less than or equal to 2, the amplitude of the triangular wave current is reduced by a second step length of 0.5mA, when the amplitude of the triangular wave current is reduced to 2.5mA, the mismatching frequency=0, and at the moment, the detection laser and the ring-down cavity 7 form single longitudinal mode matching in the frequency fluctuation range, namely the adjustment of the frequency fluctuation range of the detection laser is completed. Thereafter, the amplitude of the triangular wave current is maintained, so that the detection laser is matched with the ring-down cavity 7 in a single longitudinal mode periodically under the adjustment of the triangular wave current. The frequency of the triangular wave current can be kept unchanged all the time in the process of adjusting the frequency fluctuation range and after the adjustment is completed. In this embodiment, the amplitude of the triangular wave current is adjusted once every one period of the triangular wave, and in implementation, the initial amplitude of the triangular wave current, the initial frequency of the triangular wave current, the adjusting frequency of the triangular wave current amplitude, the matching threshold k1, the first step size and the second step size may be all selected according to actual requirements, where the first step size and the second step size may be set according to the cavity length L of the ring-down cavity 7, and as known from fsr=c/2 nL, the larger the cavity length L of the ring-down cavity 7, the smaller the value of the FSR, that is, the smaller the adjacent longitudinal mode frequency interval Δv. The smaller the adjacent longitudinal mode frequency interval deltav is, the higher the accuracy requirement for detecting laser frequency adjustment is, so that the larger the cavity length L is, the smaller the values of the first step length and the second step length are.
In order to implement the ring-down cavity longitudinal mode matching method, the invention also provides a ring-down cavity longitudinal mode matching system, which comprises a light detector connected with a CRDS platform, wherein the CRDS platform comprises a ring-down cavity 7 and a laser 6 for generating detection laser, and the detection laser is incident into the ring-down cavity 7;
When the ring-down cavity longitudinal mode matching is carried out, the working parameters of the laser 6 are adjusted to enable the frequency of the detection laser to fluctuate within an initial frequency fluctuation range, after the detection laser is incident into the ring-down cavity, the light detector is used for detecting the light beam in the ring-down cavity and generating an optical detection electric signal, and the frequency fluctuation range of the detection laser is adjusted according to the optical detection electric signal generated by the light detector until the detection laser and the ring-down cavity 7 form single longitudinal mode matching within the frequency fluctuation range.
Specifically, fig. 1 shows a schematic diagram of an embodiment of a ring-down cavity longitudinal mode matching system, wherein the optical detector is not shown in the drawings, and reference is made to the above description for specific forms of the laser 6, ring-down cavity 7 and optical detector.
Further, the ring-down cavity longitudinal mode matching system also comprises a power supply module 2, a signal wave generator 4 and a driving module 1;
The power supply module 2 is connected with the signal wave generator 4 and the driving module 1 and is used for supplying power to the signal wave generator 4 and the driving module 1;
the signal wave generator 4 is connected with the driving module 1 and the optical detector, the driving module 1 is connected with the laser 6, the signal wave generator 4 generates a signal wave voltage according to the optical detection electric signal and inputs the signal wave voltage into the driving module 1, and the driving module 1 converts the signal wave voltage into a signal wave current and inputs the signal wave current into the laser 6.
Specifically, the power supply module 2 is connected with a power supply of the CRDS platform, and the power supply module 2 has a level conversion capability and is used for converting a power supply voltage provided by the CRDS platform into a driving voltage, and the driving voltage is loaded to the signal wave generator 4 and the driving module 1 to provide working voltages for the signal wave generator 4 and the driving module 1. The signal wave generator can adopt an ARM chip of STM32F1 series, when the signal wave is triangular, the ARM chip outputs triangular wave voltage to the driving module 1 by step-type adjustment of DA code value, the driving module 1 converts the triangular wave voltage into triangular wave current and inputs the triangular wave current to the laser 6, the triangular wave current is superposed into original driving current of the laser 6 so as to adjust working current of the laser 6 based on the superposed triangular wave current, and the original driving current of the laser 6 is provided by a power supply of the CRDS platform. The specific way of outputting the triangular wave voltage to the driving module 1 by the step-by-step adjustment of the DA code value is the same as the way of outputting the triangular wave voltage by the step-by-step adjustment of the DA code value, and will not be described herein.
Further, the signal wave generator comprises a matching detection unit, a main control unit, a parameter adjusting unit and an output unit which are connected in an adapting mode.
Specifically, the matching detection unit is connected with the light detector and the main control unit, the main control unit is connected with the parameter adjusting unit, the parameter adjusting unit is connected with the output unit, and the output unit is connected with the driving unit. The matching detection unit is used for receiving the optical detection electric signal detected by the optical detector and judging the mismatching times n of the detection laser and the ring-down cavity in one period of the signal wave according to the optical detection electric signal. The main control unit is used for comparing the relation between the number of mismatching times n and the matching threshold k1, the parameter adjusting unit is used for adjusting the amplitude of the signal wave voltage according to the relation between the number of mismatching times n and the matching threshold k1 so as to adjust the amplitude of the signal wave current, and the output unit is used for outputting the signal wave voltage to the driving module 1.
Further, the ring-down cavity longitudinal mode matching system further comprises an interaction module 5, and the interaction module 5 is connected with the signal wave generator 4 through the communication interface 3.
Specifically, the power supply module 2 is connected to the interaction module 5 to provide an operating voltage for the interaction module 5. The communication interface 3 may be a serial communication interface, and the interaction module 5 may be a serial resistor screen, and when the ring-down cavity longitudinal mode matching is performed, an adjustment instruction of initial values of the signal wave amplitude and the frequency may be input to the signal wave generator 4 through the interaction module 5, so as to configure the initial values of the signal wave amplitude and the frequency.
In one embodiment of the invention, the ring down cavity longitudinal mode matching system comprises the following specific working steps:
s1, after a ring-down cavity longitudinal mode matching system is connected with a CRDS platform in an adaptive mode, determining initial frequency of detection laser according to an absorption spectrum of gas to be detected, and configuring initial working parameters of a laser 6 according to the initial frequency of the detection laser.
Specifically, the gas has selectivity to absorb light, and the same gas has different absorption effects to light at different frequencies, so that the initial frequency of the detection laser needs to be determined according to the absorption spectrum of the gas, so that the detection laser can be absorbed by the gas to be detected. The initial operating parameters of the laser 6 include the primary drive current and the operating temperature.
S2, the power supply module 2 converts the power supply voltage provided by the CRDS platform into a driving voltage so as to supply power for the driving module 1, the signal wave generator 4 and the interaction module 5.
S3, after the signal wave generator 4 is electrified and started, initial values of the voltage amplitude and the frequency of the signal wave are configured.
Specifically, since the signal wave current is converted from the signal wave voltage in the system, after determining the initial values of the signal wave current amplitude and the frequency, the initial values of the signal wave voltage amplitude and the frequency need to be configured according to the conversion relationship between the signal wave current and the signal wave voltage. Optionally, an adjustment instruction of the initial value of the voltage amplitude and the frequency of the signal wave can be input to the signal wave generator 4 through the interaction module 5, the initial value of the voltage amplitude and the frequency of the signal wave can be configured, and the initial value of the voltage amplitude and the frequency of the signal wave can also be preset in the signal wave generator 4 directly.
And S4, the signal wave generator 4 outputs a signal wave voltage to the driving module 1, and the driving module 1 converts the signal wave voltage into a signal wave current and superimposes the signal wave current on the original driving current of the laser 6 so as to enable the frequency of the detection laser to start to fluctuate.
S5, the optical detector detects the light beam in the ring-down cavity 7 and transmits the generated optical detection electric signal to the signal wave generator 4, and the signal wave generator 4 adjusts the amplitude of the signal wave voltage and the adjusting step length of the amplitude according to the optical detection electric signal, so that the amplitude of the signal wave current and the adjusting step length of the amplitude are adjusted until the detection laser and the ring-down cavity 7 form single longitudinal mode matching.
The ring-down cavity longitudinal mode matching system adopts a modularized design, can be quickly installed on different CRDS platforms for use, and can be used for quickly realizing single longitudinal mode matching between detection laser and the ring-down cavity 7 based on the ring-down cavity longitudinal mode matching method, so that the problems of low adjustment speed and low adjustment precision of the conventional longitudinal mode matching are solved.
It should be noted that the words "front", "back", "left", "right", "upper" and "lower" used in the above description refer to directions in the drawings of the present application, and the words "front" and "back", "inner" and "outer" refer to directions toward or away from, respectively, a specific component. Furthermore, the terms "first" and "second" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated.
The above is only a preferred embodiment of the present invention, and the present invention is not limited to the above examples. It is to be understood that other modifications and variations which may be directly derived or contemplated by those skilled in the art without departing from the spirit and concepts of the present invention are deemed to be included within the scope of the present invention.