Trace gas detection apparatus and method based on quantum cascade lasers

Abstract

A trace gas detection device and method based on quantum cascade laser, the device comprises a light source module, a measurement module and a data acquisition and processing module, the light source module comprises a signal generator, a laser controller, a quantum cascade laser and an optical adjustment mirror group; the measurement module comprises a gas absorption cell and a photodetector; wherein the signal generator is used for generating a current driving signal superimposed by a low-frequency pulse signal and a high-frequency sinusoidal signal, the laser controller is used for receiving the current driving signal and driving the quantum cascade laser, so as to control the quantum cascade laser to emit wavelength intermittent modulation laser, and finally demodulate the measurement signal of the measured gas to determine the concentration of the measured gas. The present application can realize high detection sensitivity of trace gas detection under the condition that the heat generation of the laser is significantly reduced, and then the external cooling system can be removed, which is beneficial to the miniaturization and light weight of the laser absorption spectrum gas sensor, and promotes its more widely application.

Description

Technical Field

[0001] This invention relates to the field of gas analysis and detection, and in particular to a trace gas detection device and method based on a quantum cascade laser. Background Technology

[0002] Laser absorption spectroscopy, as a highly selective, fast-response, and non-contact optical measurement method, has been widely used in various gas sensing fields. It utilizes the wavelength tuning characteristics of a laser, injecting a periodic continuous current signal to enable the laser to scan its output wavelength. After the laser scans across the absorption characteristic spectral lines of the gas, its spectral signal is acquired, and the concentration information of the gas being measured can then be retrieved.

[0003] For applications involving high concentrations of the gas to be measured, direct absorption spectroscopy can be used. Direct absorption spectroscopy utilizes the wavelength tuning characteristics of lasers, typically employing a continuous current signal such as a triangular wave or sawtooth wave to drive the laser for wavelength scanning. After the incident laser is absorbed by the gas, the change in the intensity of the transmitted laser is collected and compared iteratively with data in a molecular absorption spectral database to directly calculate the absolute concentration of the gas. As can be seen, direct absorption spectroscopy is a calibration-free method, but it is highly susceptible to interference from background noise.

[0004] For measurements of low gas concentrations, wavelength modulation is typically used to improve detection sensitivity. Wavelength modulation technology superimposes a high-frequency sinusoidal signal onto a low-frequency scanning signal, achieving high-frequency modulation of the gas absorption characteristics, thereby reducing low-frequency interference and improving the signal-to-noise ratio. The extracted second harmonic signal after demodulation is positively correlated with the gas concentration.

[0005] Quantum cascade lasers offer advantages such as compact structure, high laser power, and room-temperature operation, and operate in the mid-infrared band, where gas molecule absorption lines are strongest. Therefore, compared to conventional near-infrared lasers, mid-infrared quantum cascade lasers can achieve higher sensitivity gas detection as a light source for absorption spectroscopy measurements. With the rapid development of quantum cascade lasers in recent years, mid-infrared laser absorption spectroscopy technology has been widely applied in atmospheric environmental monitoring, biomedical detection, and industrial process control.

[0006] Quantum cascade lasers typically rely on semiconductor coolers to control the chip temperature. However, under continuous high-current drive, the laser chip generates significant heat, which is transferred to its hot side by the semiconductor cooler. Therefore, external active cooling is required to dissipate this heat, typically through forced air cooling or water cooling. However, the auxiliary devices for external forced cooling are relatively bulky, which is detrimental to the integration and lightweight design of sensing devices.

[0007] It should be noted that the information disclosed in the background section above is only for understanding the background of this application, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0008] The main objective of this invention is to overcome the deficiencies of the aforementioned background technology and provide a trace gas detection device and method based on a quantum cascade laser, so as to achieve high detection sensitivity of trace gases under the condition of significantly reduced heat generation of the laser, which is beneficial to the miniaturization and weight reduction of the gas detection device.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A trace gas detection device based on a quantum cascade laser includes a light source module, a measurement module, and a data acquisition and processing module. The light source module and the data acquisition and processing module are respectively coupled to the measurement module. The light source module includes a signal generator, a laser controller, a quantum cascade laser, and an optical adjustment mirror group arranged along the optical path, connected in sequence. The measurement module includes a gas absorption cell and a photodetector arranged along the optical path. The data acquisition and processing module is connected to the signal generator and the photodetector.

[0011] The signal generator generates a current-driven signal that superimposes a low-frequency pulse signal and a high-frequency sinusoidal signal. The laser controller receives the current-driven signal and drives the quantum cascade laser to control the intermittently modulated wavelength of the emitted laser. The modulated laser enters the gas absorption cell through the optical adjustment lens group. After being absorbed by the gas in the gas absorption cell, the laser is received by the photodetector. The photodetector converts the received optical signal into an electrical signal and outputs it as a measurement signal to the data acquisition and processing module. The data acquisition and processing module demodulates the measurement signal according to the laser drive reference signal input from the signal generator to obtain harmonic signals, and selects the second harmonic signal as a characterization of the concentration of the gas to be measured.

[0012] Furthermore, the laser controller includes a current control unit and a temperature control unit; the temperature control unit is used to set the temperature of the built-in semiconductor cooling chip of the quantum cascade laser and select the output laser wavelength of the quantum cascade laser according to the absorption spectrum of the gas to be measured; the current control unit is used to drive the quantum cascade laser according to the current driving signal generated by the signal generator to control the wavelength modulation of the output laser.

[0013] Furthermore, the quantum cascade laser is a distributed feedback quantum cascade laser with continuous wave output.

[0014] Furthermore, it also includes a finned heat sink base on which the quantum cascade laser is mounted.

[0015] Furthermore, the optical adjustment lens group includes several mirrors and lenses for adjusting the direction of the emitted laser and reducing the size of the laser spot.

[0016] Furthermore, the gas absorption cell is a multi-reflection cell comprising two reflectors.

[0017] Furthermore, the data acquisition and processing module includes a data acquisition card and a processing unit connected to the data acquisition card, wherein the input terminals of the data acquisition card are respectively connected to the signal generator and the photodetector.

[0018] Furthermore, the duty cycle of the low-frequency pulse current signal is adjustable but does not exceed 20%, the minimum current value within the pulse is greater than the laser's output threshold current, and the maximum current value is less than the laser's limiting current. Preferably, the minimum current value outside the pulse is slightly higher than 0.

[0019] Furthermore, the amplitude of the high-frequency sinusoidal signal is selected based on the spectral width of the absorption line of the gas to be measured in order to achieve the optimal detection signal-to-noise ratio.

[0020] A method for detecting trace gases based on quantum cascade lasers, comprising using the aforementioned trace gas detection device based on quantum cascade lasers for trace gas detection, the method comprising:

[0021] The signal generator produces a current-driven signal that superimposes a low-frequency pulse signal and a high-frequency sinusoidal signal. The laser controller receives the current-driven signal and uses it as an intermittent modulation signal to control the injection current of the quantum cascade laser, thereby controlling the quantum cascade laser to emit laser light with intermittently modulated wavelengths. The modulated laser light is absorbed by the gas to be measured along the optical path and then received by the photodetector and converted into an electrical signal. The data acquisition and processing module demodulates and filters the electrical signal according to the laser drive reference signal input from the signal generator to obtain the second harmonic signal value related to the concentration of the gas to be measured, and uses the second harmonic signal value to determine the concentration of the gas to be measured.

[0022] Furthermore, the method also includes:

[0023] The amplitude of the applied high-frequency sinusoidal signal is adjusted so that the peak-to-peak value of the second harmonic signal reaches its maximum, thereby determining the optimal modulation current value.

[0024] Furthermore, the method also includes:

[0025] Different concentrations of the target gas and non-absorbable nitrogen were introduced into the gas absorption cell to obtain the linear correlation between the second harmonic signal and the gas concentration, i.e., the calibration curve; and

[0026] A sample of the gas to be tested is extracted from a real-world scenario and introduced into the gas absorption cell. The concentration value of the gas is then retrieved based on the calibration curve.

[0027] The beneficial effects of this invention are:

[0028] This invention proposes a trace gas detection device and method based on a quantum cascade laser, which can significantly reduce the heat generated by the laser, thereby eliminating the need for an external cooling system. This invention obtains the laser absorption spectrum using an intermittently modulated quantum cascade laser, achieving high detection sensitivity for trace gases while significantly reducing laser heat generation. This facilitates the miniaturization and weight reduction of laser absorption spectroscopy gas sensors, promoting their wider application.

[0029] In summary, compared with existing trace gas detection methods based on continuous laser absorption spectroscopy, the trace gas detection device and method based on intermittently modulated quantum cascade lasers of the present invention have the following main advantages:

[0030] 1. Compared with direct absorption detection technology, the trace gas detection scheme based on intermittently modulated quantum cascade laser of the present invention can significantly improve the detection sensitivity;

[0031] 2. This invention uses an intermittent continuous wave (iCW) signal, which is based on the superposition of low-frequency pulse signals and high-frequency sinusoidal signals, as the driving current. It utilizes the chirp effect of quantum cascade lasers to achieve frequency scanning of the emitted laser. Compared with the conventional continuous wave (CW) current signal scanning, it can achieve a wider spectral coverage (generally more than twice as wide), thus enabling the detection of gas molecules with broad absorption lines.

[0032] 3. The biggest advantage of the trace gas detection scheme based on intermittently modulated quantum cascade laser of the present invention compared with the prior art is that it limits the heat generated by the laser to the pulse time range. Therefore, it can greatly reduce the heat generated by the laser, thereby eliminating the redundant external forced cooling module (generally air cooling or water cooling). This is conducive to realizing the lightweight and miniaturized design of the sensor based on the laser absorption spectroscopy method, and is suitable for the measurement needs of complex field environments. Attached Figure Description

[0033] Figure 1 This is a structural block diagram of a trace gas detection device based on a quantum cascade laser according to an embodiment of the present invention;

[0034] Figure 2 This is a schematic diagram of the modulation signal used in the trace gas detection device and method based on quantum cascade lasers according to an embodiment of the present invention;

[0035] Figure 3 This is a schematic diagram of the second harmonic signal of nitric oxide with a concentration of 20 ppm, measured by the trace gas detection device and method based on quantum cascade lasers according to an embodiment of the present invention.

[0036] Figure label:

[0037] 1. Signal generator

[0038] 2. Laser controller

[0039] 3. Quantum cascade lasers

[0040] 4. Optical adjustment lens group

[0041] 5. Gas absorption tank

[0042] 6. Photodetector

[0043] 7. Data Acquisition Card

[0044] 8. Computer Detailed Implementation

[0045] The embodiments of the present invention will be described in detail below. It should be emphasized that the following description is merely exemplary and is not intended to limit the scope and application of the present invention.

[0046] It should be noted that when a component is referred to as "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as "connected to" another component, it can be directly connected to or indirectly connected to that other component. Furthermore, a connection can be used for fixing, coupling, or communication.

[0047] It should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention.

[0048] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of embodiments of the present invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0049] See Figure 1 This invention provides a trace gas detection device based on a quantum cascade laser, comprising a light source module, a measurement module, and a data acquisition and processing module. The light source module and the data acquisition and processing module are respectively coupled to the measurement module. The light source module includes a signal generator 1, a laser controller 2, a quantum cascade laser 3, and an optical adjustment mirror group 4 arranged along the optical path, connected in sequence. The measurement module includes a gas absorption cell 5 and a photodetector 6 arranged along the optical path. The data acquisition and processing module is connected to the signal generator 1 and the photodetector 6. The signal generator 1 generates a current-driven signal that superimposes a low-frequency pulse signal and a high-frequency sinusoidal signal. The laser controller 2 receives the current-driven signal and drives the quantum cascade laser 3 to control the intermittently modulated wavelength of the quantum cascade laser emission. The modulated laser enters the gas absorption cell 5 through the optical adjustment lens group 4. After being absorbed by the gas in the gas absorption cell 5, the laser is received by the photodetector 6. The photodetector 6 converts the received optical signal into an electrical signal and outputs it as a measurement signal to the data acquisition and processing module. The data acquisition and processing module demodulates the measurement signal according to the laser drive reference signal input from the signal generator 1 to obtain harmonic signals, selects the second harmonic signal as a characterization of the concentration of the gas to be measured, and finally determines the concentration of the gas to be measured.

[0050] This invention also provides a trace gas detection method based on a quantum cascade laser. The method uses the aforementioned trace gas detection device based on a quantum cascade laser for trace gas detection. The method includes: a signal generator 1 generating a current-driven signal that superimposes a low-frequency pulse signal and a high-frequency sinusoidal signal; a laser controller 2 receiving the current-driven signal and using it as an intermittent modulation signal to control the injection current of the quantum cascade laser 3, thereby controlling the quantum cascade laser to emit laser light with intermittently modulated wavelengths; the modulated laser light being absorbed by the gas to be measured along the optical path and then received by a photodetector 6 and converted into an electrical signal; and a data acquisition and processing module demodulating and filtering the electrical signal according to the laser drive reference signal input from the signal generator 1 to obtain a second harmonic signal value related to the concentration of the gas to be measured, and using the second harmonic signal value to determine the concentration of the gas to be measured.

[0051] The trace gas detection device and method based on quantum cascade lasers provided in this invention can achieve high detection sensitivity for trace gases with a significant reduction in laser heat generation. This eliminates the need for an external cooling system, which is beneficial for the miniaturization and weight reduction of laser absorption spectroscopy gas sensors, and promotes their wider application. Specifically, the trace gas detection scheme based on intermittently modulated quantum cascade lasers of this invention can significantly improve detection sensitivity compared with direct absorption detection technology. The trace gas detection device and method of this invention use an intermittent continuous wave (iCW) signal based on the superposition of low-frequency pulse signals and high-frequency sinusoidal signals as the driving current, and utilize the chirp effect of the quantum cascade laser to achieve frequency scanning of the emitted laser. Compared with the conventional continuous wave (CW) current signal scanning, it can achieve a wider spectral coverage (generally more than twice), thus enabling the detection of gas molecules with broad absorption lines. The greatest advantage of the trace gas detection scheme based on intermittently modulated quantum cascade lasers of this invention compared with the prior art is that it limits the heat generation of the laser to the pulse time range, thus greatly reducing the heat generation of the laser and eliminating the need for redundant external forced cooling modules (generally air cooling or water cooling). This facilitates the lightweight and miniaturized design of sensors based on laser absorption spectroscopy, making them suitable for measurement needs in complex field environments.

[0052] The following describes specific embodiments of the present invention in conjunction with the accompanying drawings.

[0053] like Figure 1 As shown, the trace gas detection device based on an intermittently modulated quantum cascade laser according to an embodiment of the present invention includes a light source module, a measurement module, and a data acquisition and processing module.

[0054] The light source module includes a signal generator 1, a laser controller 2, a quantum cascade laser 3, and an optical adjustment mirror group 4. The laser selected is a distributed feedback quantum cascade laser 3 with continuous wave output, whose center wavelength corresponds to the absorption line of nitric oxide molecules around 5.2 micrometers. The laser is mounted on a finned aluminum heat sink base.

[0055] Signal generator 1 is used to generate a current drive signal that combines low-frequency pulses and high-frequency modulation, such as... Figure 2As shown. The duty cycle of the low-frequency pulsed current signal is adjustable, but does not exceed 20%. The minimum current value within the pulse is greater than the laser's output threshold current, while the maximum current value is less than the laser's limiting current. The minimum current value outside the pulse is slightly higher than 0. The amplitude of the high-frequency sinusoidal signal is selected based on the spectral width of the absorption line of the gas to be measured to achieve the optimal detection signal-to-noise ratio. The laser controller 2 includes a current control unit and a temperature control unit. The temperature control unit is used to set the temperature of the built-in semiconductor cooler of the laser and select the laser output wavelength based on the absorption spectrum of the gas to be measured. The current control unit is used to receive the current signal generated by the signal generator and then drive the laser to control the wavelength modulation of the output laser. The optical adjustment lens group 4 includes several mirrors and lenses for adjusting the direction of the output laser and shrinking the spot size.

[0056] The measurement module includes a gas absorption cell 5 and a photodetector 6. The laser beam, adjusted by the optical adjustment mirror group 4, enters the gas absorption cell 5 at a suitable angle. The gas absorption cell 5 can be a multi-reflection cell composed of two mirrors. Multiple reflections of the laser within the cell increase the optical path length for gas absorption, and this path length can be flexibly selected according to the required sensitivity and signal quality. After gas absorption, the laser beam leaves the absorption cell and is received by the photodetector 6. The photodetector 6 converts the received optical signal into an electrical signal through the photoelectric effect and outputs it to the backend data acquisition and processing module.

[0057] The data acquisition and processing module includes a data acquisition card 7 and a computer 8. The input terminals of the data acquisition card 7 are connected to the signal generator 1 and the photodetector 6, respectively. The data acquisition card 7 has a built-in lock-in amplifier, which uses the laser-driven reference signal input from the signal generator 1 and the measurement signal input from the photodetector 6 to demodulate and obtain harmonic signals. The second harmonic signal is selected as the final characterization of the gas concentration to be measured. The obtained second harmonic signal is recorded and sent to the computer 8 for data processing and analysis, including digital filtering, background subtraction, and extraction of the peak-to-peak value of the second harmonic.

[0058] Figure 3 The diagram illustrates the second harmonic signal obtained by demodulating 20 ppm nitric oxide using the trace gas detection method based on an intermittently modulated quantum cascade laser according to the present invention. Specifically, the peak-to-peak value of the signal on the right is selected as the signal value associated with the concentration of the gas to be measured.

[0059] In some embodiments, a trace gas spectroscopic detection method based on an intermittently modulated quantum cascade laser includes: a signal generator outputting a signal superimposed with a low-frequency pulse and a high-frequency sine wave, which is input to a laser controller. The laser controller uses the intermittently modulated signal to control the injection current of the quantum cascade laser, thereby modulating the emitted laser wavelength. The modulated laser is absorbed by the gas to be measured along the optical path and received by a photodetector, converted into an electrical signal. This electrical signal is input to a data acquisition card and a processing module, and after signal demodulation, filtering, and analysis, a second harmonic signal value related to the concentration of the gas to be measured is obtained.

[0060] In a preferred embodiment, the detection method may include the following steps:

[0061] (1) First, select the corresponding mid-infrared absorption line (ν0) from the high-resolution molecular absorption spectral database according to the type of gas to be measured. The selected line should meet the requirements of high absorption intensity and low interference from other gases.

[0062] (2) For the absorption spectrum of the target gas, select a quantum cascade laser that can emit the corresponding wavelength as the detection light source.

[0063] (3) Adjust the parameters of the laser controller (including the current control unit and the temperature unit), wherein the current control unit is triggered by a pulse signal generated by the signal generator (duty cycle not exceeding 20%). The current within the pulse is greater than the laser's output threshold current, but less than the laser's limiting current; the current outside the pulse is slightly higher than 0 to ensure safe operation of the laser. Ultimately, the output laser wavelength of the quantum cascade laser covers the absorption spectrum (ν0) of the target gas within the pulse time;

[0064] (4) The signal generator generates a superimposed signal of low-frequency pulse and high-frequency (f) sine wave, which is input to the laser controller to intermittently modulate the output wavelength of the quantum cascade laser. The superimposed signal also ensures that the minimum current value within the pulse is greater than the laser's output threshold current, while the maximum current value is less than the laser's limiting current, and the minimum current value outside the pulse is slightly higher than 0.

[0065] (5) The emitted laser from the modulated quantum cascade laser is adjusted by the optical mirror group and enters the gas absorption cell at a suitable angle, forming a preset multiple reflection mode to increase the optical path of gas absorption.

[0066] (6) The laser intensity signal after being absorbed by the gas to be measured along the optical path by the mid-infrared laser reflected multiple times in the absorption cell is collected by the photoelectric detection unit and sent to the data acquisition and analysis unit for demodulation to obtain the second harmonic signal (Y). 2f );

[0067] (7) Adjust the amplitude of the applied sinusoidal modulation current signal so that the peak-to-peak value of the second harmonic signal obtained in step (7) reaches the maximum, thereby determining the optimal modulation current value.

[0068] (8) Different concentrations of the gas to be tested and nitrogen gas without absorption are introduced into the gas absorption cell to obtain the linear correlation between the second harmonic signal and the gas concentration, i.e., the calibration curve.

[0069] (9) Extract the gas sample to be tested in the actual scenario and enter the absorption cell. Based on the calibration curve in step (8), retrieve the concentration value of the gas to be tested.

[0070] This invention enables rapid measurement of extremely low concentrations of gas in the low-heat-dissipation operating mode of this type of laser, thus making it widely applicable to trace gas detection in scenarios such as air pollution, industrial process control, and exhaust emissions from power plants.

[0071] The background section of this invention may include background information about the problems or environment in which the invention is being developed, and is not necessarily a description of prior art. Therefore, the content included in the background section does not constitute an admission of prior art by the applicant.

[0072] The above description provides a further detailed explanation of the present invention in conjunction with specific / preferred embodiments, and it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various substitutions or modifications can be made to these described embodiments without departing from the concept of the present invention, and all such substitutions or modifications should be considered within the scope of protection of the present invention. In the description of this specification, the reference to terms such as "an embodiment," "some embodiments," "preferred embodiment," "example," "specific example," or "some examples," etc., indicates that the specific features, structures, materials, or characteristics described in connection with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any suitable manner in one or more embodiments or examples. Without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification and the features of different embodiments or examples. Although the embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions, and modifications can be made herein without departing from the scope of protection of the patent application.

Claims

1. A quantum cascade laser-based trace gas detection apparatus, characterized by, The system includes a light source module, a measurement module, and a data acquisition and processing module, with the light source module and the data acquisition and processing module respectively coupled to the measurement module. The light source module includes a signal generator, a laser controller, a quantum cascade laser, and an optical adjustment mirror group arranged along the optical path, connected in sequence. The measurement module includes a gas absorption cell and a photodetector arranged along the optical path. The data acquisition and processing module is connected to the signal generator and the photodetector. The signal generator generates a current-driven signal that superimposes a low-frequency pulse signal and a high-frequency sinusoidal signal. The duty cycle of the low-frequency pulse signal is adjustable but does not exceed 20%. The laser controller receives the current-driven signal and drives the quantum cascade laser, causing the quantum cascade laser to generate a chirp effect under the action of the low-frequency pulse signal. The chirp effect is used to achieve frequency scanning of the emitted laser. Simultaneously, wavelength modulation is achieved through the high-frequency sinusoidal signal, thereby controlling the quantum cascade laser to emit intermittently modulated laser light. The modulated laser light enters the gas absorption cell through the optical adjustment lens group. After being absorbed by the gas in the gas absorption cell, the laser light is received by the photodetector. The photodetector converts the received optical signal into an electrical signal and outputs it as a measurement signal to the data acquisition and processing module. The data acquisition and processing module demodulates the measurement signal according to the laser drive reference signal input from the signal generator to obtain harmonic signals, and selects the second harmonic signal as a characterization of the concentration of the gas to be measured.

2. The quantum cascade laser-based trace gas sensing apparatus of claim 1, wherein, The laser controller includes a current control unit and a temperature control unit; the temperature control unit is used to set the temperature of the built-in semiconductor cooling chip of the quantum cascade laser and select the output laser wavelength of the quantum cascade laser according to the absorption spectrum of the gas to be measured. The current control unit is used to drive the quantum cascade laser according to the current drive signal generated by the signal generator, so as to control the wavelength modulation of the emitted laser.

3. The trace gas detection device based on quantum cascade laser according to claim 1, characterized in that, The quantum cascade laser is a distributed feedback quantum cascade laser with continuous wave output.

4. The trace gas detection device based on a quantum cascade laser according to claim 1, characterized in that, It also includes a finned heat sink base on which the quantum cascade laser is mounted.

5. The trace gas detection device based on a quantum cascade laser according to claim 1, characterized in that, The optical adjustment lens group includes several mirrors and lenses, used to adjust the direction of the emitted laser and reduce the size of the laser spot.

6. The trace gas detection device based on quantum cascade laser according to claim 1, characterized in that, The gas absorption cell is a multi-reflection cell comprising two reflectors.

7. The trace gas detection device based on a quantum cascade laser according to claim 1, characterized in that, The data acquisition and processing module includes a data acquisition card and a processing unit connected to the data acquisition card. The input terminals of the data acquisition card are connected to the signal generator and the photodetector, respectively.

8. The trace gas detection device based on a quantum cascade laser according to any one of claims 1 to 7, characterized in that, The minimum current value within the pulse is greater than the laser's output threshold current, while the maximum current value is less than the laser's limiting current, and the minimum current value outside the pulse is slightly higher than 0.

9. The trace gas detection device based on a quantum cascade laser according to any one of claims 1 to 7, characterized in that, The amplitude of the high-frequency sinusoidal signal is selected based on the spectral width of the absorption line of the gas to be measured in order to achieve the optimal detection signal-to-noise ratio.

10. The trace gas detection device based on a quantum cascade laser according to any one of claims 1 to 7, characterized in that, The quantum cascade laser utilizes the chirping effect generated by low-frequency pulse signals to achieve frequency scanning of the emitted laser, and its frequency scanning range is greater than that of the continuous wave driving mode.

11. A method for detecting trace gases based on quantum cascade lasers, characterized in that, Trace gas detection is performed using the trace gas detection device based on a quantum cascade laser according to any one of claims 1 to 10, the method comprising: The signal generator produces a current-driven signal that superimposes a low-frequency pulse signal and a high-frequency sinusoidal signal. The laser controller receives the current-driven signal and uses it as an intermittent modulation signal to control the injection current of the quantum cascade laser. The quantum cascade laser generates a chirp effect under the action of the low-frequency pulse signal, and uses the frequency drift caused by the chirp effect to achieve frequency scanning of the absorption spectrum of the gas to be measured. At the same time, the superimposed high-frequency sinusoidal signal generates harmonic signals related to the absorption of the gas to be measured. The modulated laser is absorbed by the gas to be measured and then received by a photodetector and converted into an electrical signal. The data acquisition and processing module demodulates the reference signal to obtain the second harmonic signal value and uses the second harmonic signal value to determine the concentration of the gas to be measured. The quantum cascade laser operates with a duty cycle of no more than 20% and uses the chirp effect to achieve frequency scanning, thereby completing gas detection without the need for an external forced cooling system.

12. The method according to claim 11, characterized in that, The frequency scanning range generated by the chirping effect is greater than the frequency scanning range in the continuous wave drive mode.

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