Gas detection device and method based on pulse width modulation and cavity ring-down spectroscopy

Abstract

The invention discloses a gas detection device and method based on pulse width modulation and cavity ring-down spectroscopy, and relates to the technical field of gas detection, in the device, a pulse adjustable laser emission module is connected with a data processing module, the pulse adjustable laser emission module emits laser, and the laser wavelength is adjusted by using pulse current; the optical ring-down cavity assembly is used for containing gas to be detected; the optical ring-down cavity assembly further reflects the laser for multiple times, and the path of the laser in the optical ring-down cavity assembly is prolonged; the photoelectric detector obtains a detection signal; the detection signal is a residual laser signal after the laser is absorbed by the to-be-detected gas in a multi-reflection process; the data processing module is also connected with the photoelectric detector; the data processing module converts the detection signal into an electric signal, inversion is carried out according to the electric signal, and the concentration of the to-be-detected gas is obtained.According to the gas detection device, by arranging the pulse-adjustable laser emission module, the size of the gas detection device is reduced when the frequency modulation range of the laser driving current is enlarged.

Description

Technical Field

[0001] The present application relates to the technical field of gas detection, and in particular to a gas detection device and method based on pulse width modulation and cavity ring-down spectroscopy. Background Art

[0002] Cavity Ring-Down Spectroscopy (CRDS) is a highly sensitive spectroscopy technique that can be used for quantitative detection of extremely low concentration gases and is widely used in gas detection, environmental monitoring, chemical analysis and other fields. The CRDS system uses multiple reflections of light in a high-reflectivity optical cavity to accurately detect the absorption signal of a gas or substance. Its core principle is to measure the ring-down time of light in an optical cavity. The change in the ring-down time is proportional to the concentration of the absorbing substance (such as gas) in the cavity. Due to its extreme sensitivity to optical losses, CRDS exhibits extremely high accuracy and sensitivity when detecting trace gases and weakly absorbing substances. However, the key problem faced by CRDS technology in practical applications is how to achieve accurate scanning of the target absorption spectrum so that the laser mode matches the ring-down cavity mode to ensure a stable ring-down signal. At the same time, how to quickly shut down the cavity mode signal after it is generated is also a key indicator affecting the accuracy of the CRDS system. Currently, shutting down the laser usually relies on a complex laser shut-off device, which increases the complexity, volume and cost of the system. Traditionally, CRDS systems have relied on mechanical tuning devices and current-based wavelength tuning to achieve wavelength tuning.

[0003] The current-based wavelength tuning CRDS method directly changes the driving current of the injected laser to achieve linear scanning of the wavelength. The steps are as follows: the host computer controls the signal generating device to send a given voltage signal to the laser driver; the laser driver converts the voltage signal into a current signal to drive the laser to emit light; the laser is reflected by the photodetector after entering the optical resonant cavity; the photodetector receives the ring-down signal and transmits it to the host computer for threshold judgment; after the ring-down signal reaches the threshold, the host computer controls the acousto-optic modulator (AOM) or electro-optic modulator (EOM) to turn off the laser; the host computer collects the ring-down signal after the laser is turned off and performs signal processing; the host computer inverts the concentration and outputs the concentration data. This method directly changes the driving current of the injected laser to achieve linear drift of the wavelength. It has a simple structure, but the tuning range is small and is easily affected by current fluctuations. It often requires the use of expensive optical switches and AOMs or EOMs. The CRDS method based on mechanical tuning usually uses mechanical components such as piezoelectric ceramics, rotating prisms, tuning forks, etc. to change the output optical path of the laser and thus tune the wavelength. Such methods have complex structures and large volumes, making it difficult to meet the needs of portable or on-site real-time detection. Summary of the invention

[0004] The purpose of the present application is to provide a gas detection device and method based on pulse width modulation and cavity ring-down spectroscopy, which can reduce the volume of the gas detection device while increasing the frequency modulation range of the laser driving current.

[0005] To achieve the above objectives, this application provides the following solutions:

[0006] In a first aspect, the present application provides a gas detection device based on pulse width modulation and cavity ring-down spectroscopy, comprising:

[0007] Pulse adjustable laser emission module, optical ring-down cavity assembly, photoelectric detector and data processing module;

[0008] The pulse adjustable laser emission module is connected to the data processing module, and the pulse adjustable laser emission module is used to emit laser and adjust the laser wavelength by using pulse current;

[0009] The optical ring-down cavity assembly is used to contain the gas to be tested;

[0010] The optical ring-down cavity component is also used to reflect the laser multiple times to extend the path of the laser in the optical ring-down cavity component;

[0011] The photoelectric detector is used to obtain a detection signal; the detection signal is the remaining laser signal after the laser is absorbed by the gas to be detected during multiple reflections;

[0012] The data processing module is also connected to the photoelectric detector; the data processing module is used to convert the detection signal into an electrical signal, and perform inversion according to the electrical signal to obtain the concentration of the gas to be measured.

[0013] Optionally, the pulse adjustable laser emission module includes:

[0014] Tunable lasers and direct digital frequency synthesizers;

[0015] The direct digital frequency synthesizer is connected to the tunable laser and the data processing module respectively;

[0016] The tunable laser is used to emit laser light;

[0017] The direct digital frequency synthesizer is used to generate a pulse current to control the temperature of the tunable laser and complete wavelength tuning;

[0018] The data processing module feedback controls the closing of the digital frequency synthesizer to control the start and stop of the tunable laser.

[0019] Optionally, the pulse adjustable laser emission module further includes:

[0020] Temperature controller;

[0021] The temperature controller is connected to the tunable laser and the data processing module respectively;

[0022] The temperature controller is used to operate when the temperature of the tunable laser reaches a damage temperature value, and control the temperature of the tunable laser to be lower than the damage temperature value.

[0023] Optionally, the optical ring-down cavity component comprises:

[0024] Gas pool;

[0025] The gas pool is used to contain the gas to be tested.

[0026] Optionally, the optical ring-down cavity component further includes:

[0027] Multiple reflectors;

[0028] A plurality of reflectors are arranged on the inner wall of the gas pool, and are arranged at a preset angle with the inner wall of the gas pool;

[0029] A plurality of reflecting mirrors are used to reflect the laser light multiple times, thereby extending the path of the laser light in the gas pool.

[0030] Optionally, the reflectivity of the plurality of reflectors is greater than a preset reflectivity.

[0031] Optionally, the optical ring-down cavity component further includes:

[0032] Drying device;

[0033] The drying device is connected to the inlet of the gas pool and the gas source to be tested respectively;

[0034] The drying device is used to dry the gas to be tested that enters the gas pool.

[0035] Optionally, the optical ring-down cavity component further includes:

[0036] air pump;

[0037] The air pump is connected to the outlet of the gas pool;

[0038] The air pump is used to extract the gas to be tested.

[0039] Optionally, the data processing module includes:

[0040] analog-to-digital converters and computers;

[0041] The analog-to-digital converter is connected to the photoelectric detector and the computer respectively;

[0042] The photodetector is used to convert the detection signal into an electrical signal;

[0043] The computer is used to perform inversion according to the electrical signal to obtain the concentration of the gas to be measured.

[0044] In a second aspect, the present application provides a gas detection method based on pulse width modulation and cavity ring-down spectroscopy, wherein the gas detection method based on pulse width modulation and cavity ring-down spectroscopy is applied to the gas detection device based on pulse width modulation and cavity ring-down spectroscopy, and the gas detection method based on pulse width modulation and cavity ring-down spectroscopy comprises:

[0045] Generate pulse current based on the pulse width modulation principle to adjust the laser wavelength;

[0046] Acquire a detection signal; the detection signal is the remaining laser signal after the laser is absorbed by the gas to be detected during multiple reflections;

[0047] converting the detection signal into an electrical signal;

[0048] The electric signal is inverted to obtain the concentration of the gas to be measured.

[0049] According to the specific embodiments provided in this application, this application discloses the following technical effects:

[0050] The present application provides a gas detection device and method based on pulse width modulation and cavity ring-down spectroscopy, which uses pulse current to quickly adjust the laser temperature and thus change the laser wavelength. This method has a fast response speed and can achieve more efficient wavelength scanning compared to traditional temperature control systems; in the CRDS system, temperature tuning technology is combined to detect the absorption characteristics of the gas through the change of the light ring-down time in the optical cavity. This solution simplifies the system design, improves the detection efficiency, ensures the high accuracy of gas detection, simplifies the system design, reduces the dependence on expensive laser shutoff devices and complex temperature control equipment, and reduces the system cost and volume. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0052] Figure 1 The figure is a schematic diagram of the structure of a gas detection device based on pulse width modulation and cavity ring-down spectroscopy in one embodiment of the present application. DETAILED DESCRIPTION

[0053] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0054] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0055] In an exemplary embodiment, Figure 1As shown, a gas detection device based on pulse width modulation and cavity ring-down spectroscopy is provided, comprising: a pulse adjustable laser emission module, an optical ring-down cavity component, a photodetector and a data processing module; the pulse adjustable laser emission module is connected to the data processing module, the pulse adjustable laser emission module is used to emit laser, and use pulse current to adjust the laser wavelength; the optical ring-down cavity component is used to contain the gas to be measured; the optical ring-down cavity component is also used to reflect the laser multiple times, and extend the path of the laser in the optical ring-down cavity component; the photodetector is used to obtain the detection signal; after the data received by the data processing module reaches the set threshold, it is fed back to the direct digital frequency synthesizer to turn off the laser, and the signal detected by the photodetector is the laser signal remaining after the laser is absorbed by the gas to be measured during the multiple reflections after being turned off; the data processing module is also connected to the photodetector; the data processing module is used to convert the detection signal into an electrical signal, and invert according to the electrical signal to obtain the concentration of the gas to be measured.

[0056] The pulse tunable laser emission module includes: a tunable laser, a direct digital frequency synthesizer and a temperature controller; the direct digital frequency synthesizer is connected to the tunable laser and the data processing module respectively; the tunable laser is used to emit laser; the direct digital frequency synthesizer is used to generate pulse current to control the temperature of the tunable laser and complete wavelength tuning; the data processing module feedback controls to turn off the digital frequency synthesizer to control the start and stop of the tunable laser; the temperature controller is connected to the tunable laser and the data processing module respectively; the temperature controller is used to operate when the temperature of the tunable laser reaches a damage temperature value, and control the temperature of the tunable laser to be lower than the damage temperature value.

[0057] The optical ring-down cavity assembly includes: a gas pool, a drying device, an air pump and a plurality of reflectors. The gas pool is used to contain the gas to be tested. The plurality of reflectors are arranged on the inner wall of the gas pool; and are arranged at a preset angle with the inner wall of the gas pool; the plurality of reflectors are used to reflect the laser multiple times to extend the path of the laser in the gas pool. The reflectivities of the plurality of reflectors are all greater than the preset reflectivity. The drying device is respectively connected to the inlet of the gas pool and the source of the gas to be tested; the drying device is used to dry the gas to be tested entering the gas pool. The air pump is connected to the outlet of the gas pool; the air pump is used to extract the gas to be tested.

[0058] The data processing module includes: an analog-to-digital converter and a computer; the analog-to-digital converter is connected to the photoelectric detector and the computer respectively; the photoelectric detector is used to convert the detection signal into an electrical signal; the computer is used to perform inversion according to the electrical signal to obtain the concentration of the gas to be measured.

[0059] This embodiment adjusts the laser temperature by pulse current. Compared with the traditional CRDS system, this application simplifies the system structure and reduces the cost, and is particularly suitable for the application of portable CRDS system. In addition, this application ensures the tuning accuracy and ensures the high sensitivity and accuracy of gas detection. The temperature-tuned CRDS system of this application includes the following main parts:

[0060] 1) Laser (DFB, Distributed Feedback Laser): A tunable laser whose wavelength is sensitive to temperature and wavelength scanning is achieved through temperature tuning.

[0061] 2) Direct Digital Synthesis (DDS): used to generate pulse current, control the temperature change of the laser, and achieve fast wavelength tuning.

[0062] 3) Optical Ring-down Cavity: It is composed of mirrors with high reflectivity and is used to reflect the laser multiple times to increase the path length of the light, thereby amplifying the absorption signal of the gas.

[0063] 4) Photodetector (PD): used to detect the optical ring-down signal in the optical cavity and convert it into an electrical signal for subsequent analysis.

[0064] 5) Analog-to-Digital (AD): collects the electrical signals converted by the detector and transmits them to the host computer for subsequent processing.

[0065] 6) Computer: Fit the optical ring-down signal collected by AD, perform signal processing, calculate the ring-down time, and invert the gas concentration.

[0066] 7) Drying Agent: Dry the gas entering the gas pool to eliminate the interference of water vapor on the system.

[0067] 8) Air pump (Pumb): used to extract the gas to be tested.

[0068] 9) Temperature Controller (TC): Prevents the laser from overheating and damage.

[0069] This embodiment introduces pulse current to control the temperature tuning of the laser, aiming to solve the speed and cost problems in traditional temperature tuning. By applying pulse current to the laser, the temperature of the laser is instantly changed, thereby achieving wavelength tuning. This is particularly suitable for application scenarios that do not require high scanning speed but want to simplify system design and reduce costs.

[0070] In an exemplary embodiment, a gas detection method based on pulse width modulation and cavity ring-down spectroscopy is provided. The gas detection method based on pulse width modulation and cavity ring-down spectroscopy is applied to the gas detection device based on pulse width modulation and cavity ring-down spectroscopy. The gas detection method based on pulse width modulation and cavity ring-down spectroscopy includes:

[0071] Step 1: Generate pulse current based on the pulse width modulation principle to adjust the laser wavelength.

[0072] Step 2: Obtain a detection signal; the detection signal is the remaining laser signal after the laser is absorbed by the gas to be measured during multiple reflections.

[0073] Step 3: Convert the detection signal into an electrical signal.

[0074] Step 4: Invert the electrical signal to obtain the concentration of the gas to be measured.

[0075] This application proposes a PWM-CRDS method based on temperature tuning, which uses pulse current to quickly change the temperature of the laser to achieve wavelength tuning, thereby matching the laser mode with the cavity mode to achieve the effect of detecting the substance being measured. Specifically, it includes the following steps:

[0076] 1) Pulse current control:

[0077] This application adopts a pulse current control system to achieve precise adjustment of current intensity and pulse duration to achieve rapid and stable changes in laser temperature. Compared with traditional temperature control systems, pulse current control systems have faster response speeds, can achieve rapid heating and cooling, and significantly improve the speed and stability of wavelength tuning.

[0078] 2) Rapid adjustment of laser operating temperature:

[0079] Apply pulse current to the laser to change the operating temperature of the laser through instantaneous current. Since the laser wavelength is very sensitive to temperature changes, rapid changes in temperature will cause corresponding drifts in the laser wavelength.

[0080] 3) Temperature tuning wavelength scanning:

[0081] Through pulse current regulation, the operating temperature of the laser increases or decreases rapidly, so that the wavelength can be tuned and scanned between different gas absorption peaks. When the laser mode meets the standing wave condition in the cavity, the laser mode matches the cavity mode and forms a cavity mode signal.

[0082] 4) Optical cavity ring-down signal detection:

[0083] When the cavity mode signal reaches the shutdown threshold, the pulse current is turned off. At this time, the system collects the ring-down signal after the laser is turned off.

[0084] 5) Signal processing:

[0085] The collected signal is denoised, averaged and exponentially fitted to calculate the ring-down time, and the gas concentration is calculated through the calibration curve.

[0086] The temperature tuning method in this embodiment is applicable to the detection of multiple gases: by scanning multiple wavelengths at different temperatures, the absorption peaks of different gases can be covered, and the simultaneous detection of multiple gases can be achieved. For example, in environmental monitoring, the system can detect multiple greenhouse gases such as methane and carbon dioxide through temperature tuning.

[0087] Through the temperature tuning method, the laser wavelength is precisely tuned, and combined with the CRDS technology for gas detection. By applying a pulse current to the laser to achieve rapid temperature changes, precise tuning of the wavelength is achieved. Its main purpose is to simplify the tuning device. This application reduces the dependence on high-cost temperature control equipment and laser shutoff devices, and reduces the manufacturing and maintenance costs of the overall system. Suitable for low-cost and efficient gas detection applications. This embodiment uses a pulse current to adjust the laser temperature. Compared with the traditional temperature control system, it has a simpler structure and can be integrated to reduce the size and cost. By simplifying the system design, the dependence on mechanical and complex laser shutoff equipment is reduced, thereby reducing the system cost and volume, which is suitable for portable CRDS systems.

[0088] The technical features of the above embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0089] This article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, according to the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A gas detection device based on pulse width modulation and cavity ring-down spectroscopy, characterized in that: include: Pulse adjustable laser emission module, optical ring-down cavity assembly, photoelectric detector and data processing module; The pulse adjustable laser emission module is connected to the data processing module, and the pulse adjustable laser emission module is used to emit laser and adjust the laser wavelength by using pulse current; The optical ring-down cavity assembly is used to contain the gas to be tested; The optical ring-down cavity component is also used to reflect the laser multiple times to extend the path of the laser in the optical ring-down cavity component; The photoelectric detector is used to obtain a detection signal; the detection signal is the remaining laser signal after the laser is absorbed by the gas to be detected during multiple reflections; The data processing module is also connected to the photoelectric detector; the data processing module is used to convert the detection signal into an electrical signal, and perform inversion according to the electrical signal to obtain the concentration of the gas to be measured.

2. The gas detection device based on pulse width modulation and cavity ring-down spectroscopy according to claim 1 is characterized in that: The pulse adjustable laser emission module comprises: Tunable lasers and direct digital frequency synthesizers; The direct digital frequency synthesizer is connected to the tunable laser and the data processing module respectively; The tunable laser is used to emit laser light; The direct digital frequency synthesizer is used to generate a pulse current to control the temperature of the tunable laser and complete wavelength tuning; The data processing module feedback controls the closing of the digital frequency synthesizer to control the start and stop of the tunable laser.

3. The gas detection device based on pulse width modulation and cavity ring-down spectroscopy according to claim 2 is characterized in that: The pulse adjustable laser emission module also includes: Temperature controller; The temperature controller is connected to the tunable laser and the data processing module respectively; The temperature controller is used to operate when the temperature of the tunable laser reaches a damage temperature value, and control the temperature of the tunable laser to be lower than the damage temperature value.

4. The gas detection device based on pulse width modulation and cavity ring-down spectroscopy according to claim 1, characterized in that: The optical ring-down cavity assembly comprises: Gas pool; The gas pool is used to contain the gas to be tested.

5. The gas detection device based on pulse width modulation and cavity ring-down spectroscopy according to claim 4 is characterized in that: The optical ring-down cavity assembly further comprises: Multiple reflectors; A plurality of reflectors are arranged on the inner wall of the gas pool, and are arranged at a preset angle with the inner wall of the gas pool; A plurality of reflecting mirrors are used to reflect the laser light multiple times, thereby extending the path of the laser light in the gas pool.

6. The gas detection device based on pulse width modulation and cavity ring-down spectroscopy according to claim 5, characterized in that: The reflectivity of the plurality of reflectors is greater than a preset reflectivity.

7. The gas detection device based on pulse width modulation and cavity ring-down spectroscopy according to claim 5, characterized in that: The optical ring-down cavity assembly further comprises: Drying device; The drying device is connected to the inlet of the gas pool and the gas source to be tested respectively; The drying device is used to dry the gas to be tested that enters the gas pool.

8. The gas detection device based on pulse width modulation and cavity ring-down spectroscopy according to claim 7, characterized in that: The optical ring-down cavity assembly further comprises: air pump; The air pump is connected to the outlet of the gas pool; The air pump is used to extract the gas to be tested.

9. The gas detection device based on pulse width modulation and cavity ring-down spectroscopy according to claim 8, characterized in that: The data processing module comprises: analog-to-digital converters and computers; The analog-to-digital converter is connected to the photoelectric detector and the computer respectively; The photodetector is used to convert the detection signal into an electrical signal; The computer is used to perform inversion according to the electrical signal to obtain the concentration of the gas to be measured.

10. A gas detection method based on pulse width modulation and cavity ring-down spectroscopy, characterized in that: The gas detection method based on pulse width modulation and cavity ring-down spectroscopy is applied to the gas detection device based on pulse width modulation and cavity ring-down spectroscopy as claimed in any one of claims 1 to 9, and the gas detection method based on pulse width modulation and cavity ring-down spectroscopy comprises: Generate pulse current based on the pulse width modulation principle to adjust the laser wavelength; Acquire a detection signal; the detection signal is the remaining laser signal after the laser is absorbed by the gas to be detected during multiple reflections; converting the detection signal into an electrical signal; The electric signal is inverted to obtain the concentration of the gas to be measured.

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