Multi-gas concentration detection method and device and semiconductor laser

Abstract

The invention discloses a multi-gas concentration detection method, a multi-gas concentration detection device and a semiconductor laser, and belongs to the technical field of gas detection. A quantum cascade laser with a Fabry-Perot resonant cavity and without a grating structure is adopted; the method comprises the following steps of: adjusting the temperature of a heat sink and a driving current to obtain a wavelength scanning window suitable for simultaneously detecting the concentrations of various gases, so that the absorption peaks of the various gases are in a scanning range of a laser central wavelength, and then controlling a quantum cascade laser to be in a preset time of the wavelength scanning window, enabling laser to pass through the various gases to obtain change signals of the absorption intensity of the various gases to the laser, and calculating the concentration of the various gases based on the change signals of the absorption intensity of the various gases to the laser. According to the invention, the concentration of various gases can be rapidly and accurately detected at the same time, the structure is simple, the production cost is low, the applicable detection range is wide, and the application value is high.

Description

Technical Field

[0001] The present application relates to the technical field of gas detection based on semiconductor lasers, and more specifically, to a method and device for detecting multi-gas concentration and a semiconductor laser. Background Art

[0002] In some application scenarios of gas detection, such as breath monitoring, chemical reaction monitoring, etc., it is necessary to continuously and rapidly monitor the change of concentration components of multiple gases to be detected. The existing system for detecting gas concentration based on a distributed feedback (DFB) quantum cascade laser (QCL) adopts a complex distributed feedback grating structure and operates in a single resonant cavity mode. This structure requires additional high-precision lithography process steps, has a high cost and a yield problem. In addition, the distributed feedback grating structure mainly uses temperature change to modulate the wavelength of the laser. Since the wavelength modulation coefficient of this laser with respect to temperature is low and the temperature regulation is relatively slow, it is difficult to adjust the wavelength range of the laser over a large range in a short time and it is not applicable to the rapid and accurate detection of the concentration of multiple gases simultaneously. Therefore, an improved technical solution is urgently needed to solve the above technical problems. Summary of the Invention

[0003] In view of this, the present application provides a method and device for detecting multi-gas concentration and a semiconductor laser. By using a quantum cascade laser without a grating structure, it can simultaneously and rapidly and accurately detect the concentration of multiple gases. Moreover, due to the simple structure of the laser, the production cost is low, the applicable detection range is wide, and it has great application value.

[0004] In a first aspect, an embodiment of the present application provides a method for detecting multi-gas concentration, which is applicable to a quantum cascade laser having a Fabry-Perot resonant cavity. The method includes: Pre-characterizing the quantum cascade laser, and obtaining a wavelength scanning window suitable for detecting the concentration of multiple gases by adjusting the heat sink temperature and drive current of the quantum cascade laser. In the wavelength scanning window, within a preset time, the laser linewidth of the quantum cascade laser is less than a first threshold, and the moving range of the laser center wavelength of the quantum cascade laser is greater than a second threshold so that the absorption peaks of the multiple gases are within the scanning range of the laser center wavelength; Controlling the quantum cascade laser to pass the laser emitted by the quantum cascade laser through the multiple gases within the preset time of the wavelength scanning window, obtaining a change signal of the absorption intensity of the multiple gases to the laser, and calculating the concentration of the multiple gases based on the change signal of the absorption intensity of the multiple gases to the laser.

[0005] Optionally, the pre-characterization of the quantum cascade laser to obtain a wavelength scanning window suitable for simultaneously detecting the concentrations of multiple gases by adjusting the heat sink temperature and driving current of the quantum cascade laser includes: Dividing a predetermined temperature range of the heat sink temperature into N temperature intervals, dividing a predetermined current range of the driving current into M current intervals, and arranging and combining the N temperature intervals and M current intervals to form experimental data of an N*M matrix, where N and M are integers greater than 1; According to the wavelength scanning window, obtaining target values of the heat sink temperature and driving current that satisfy the wavelength scanning window from the experimental data of the N*M matrix.

[0006] Optionally, the pre-characterization of the quantum cascade laser to obtain a wavelength scanning window suitable for simultaneously detecting the concentrations of multiple gases by adjusting the heat sink temperature and driving current of the quantum cascade laser includes: obtaining a first functional relationship between the laser center wavelength and time within the wavelength scanning window, and the first functional relationship is , where λ is the laser center wavelength, t is the preset time of the wavelength scanning window, and tb and te respectively represent the start time and end time of the preset time of the wavelength scanning window.

[0007] Optionally, within the wavelength scanning window, the center wavelength of the laser moves unidirectionally towards a longer wavelength or a shorter wavelength as time increases, and the first functional relationship is repeatable in multiple measurements exceeding a predetermined number of times, and the change in the center wavelength is less than a predetermined percentage threshold.

[0008] Optionally, controlling the quantum cascade laser to pass the laser emitted by the quantum cascade laser through the multiple gases within the preset time of the wavelength scanning window to obtain a change signal of the absorption intensity of the multiple gases to the laser includes: Within the preset time of the wavelength scanning window, splitting the laser emitted by the quantum cascade laser and passing it through a reference gas chamber and a gas chamber to be measured respectively, and obtaining a first current value of the intensity of the laser in the gas chamber to be measured changing with time and a second current value of the intensity of the laser in the reference gas chamber changing with time respectively; Calculating the ratio between the first current value of the intensity of the laser in the gas chamber to be measured changing with time and the second current value of the intensity of the laser in the reference gas chamber changing with time to obtain a change signal of the absorption intensity of the multiple gases in the gas chamber to be measured to the laser , where .

[0009] Optionally, calculating the concentrations of the multiple gases based on the change signal of the absorption intensity of the laser by the multiple gases includes: Based on and the first functional relationship the inverse function of calculate the second functional relationship of the absorption intensity of the multiple gases for the laser varying with the central wavelength , ; According to the second functional relationship of the absorption intensity of the multiple gases for the laser varying with the central wavelength , obtain the intensity of the absorption peak of each gas in the multiple gases, and calculate the concentration of each gas according to the intensity of the absorption peak of each gas.

[0010] Optionally, according to the second functional relationship of the absorption intensity of the multiple gases for the laser varying with the central wavelength , obtain the intensity of the absorption peak of each gas in the multiple gases, and calculate the concentration of each gas according to the intensity of the absorption peak of each gas includes: According to the second functional relationship of the absorption intensity of the multiple gases for the laser varying with the central wavelength , obtain the intensities of multiple absorption peaks of each gas in the multiple gases; Calculate the multiple concentration values corresponding to each gas according to the intensities of the multiple absorption peaks of each gas, and calculate the average value of the multiple concentration values as the final concentration value of each gas.

[0011] Optionally, according to the second functional relationship of the absorption intensity of the multiple gases for the laser varying with the central wavelength , obtain the intensity of the absorption peak of each gas in the multiple gases, and calculate the concentration of each gas according to the intensity of the absorption peak of each gas includes: According to the second functional relationship of the absorption intensity of the multiple gases for the laser varying with the central wavelength , obtain the intensities of multiple superimposed absorption peaks of the multiple gases; Construct a system of multiple equations according to the intensities of the multiple superimposed absorption peaks and the absorption coefficients of the multiple gases involved in each superimposed absorption peak, and calculate the concentration values corresponding to each gas by solving the system of equations.

[0012] Optionally, the first threshold is 1 cm -1 , and the second threshold is 10 cm -1 .

[0013] Optionally, the predetermined temperature range of the heat sink temperature is 0 to 30 degrees Celsius, the predetermined current range of the drive current is 1 to 3 times the threshold current of the quantum cascade laser, the range of each temperature interval is 1 to 3 degrees Celsius, and the range of the current interval is 0.1 to 0.4 times the threshold current.

[0014] In a second aspect, an embodiment of the present application further provides a multi-gas concentration detection device, which is applicable to the detection method according to any of the foregoing embodiments, and includes: a quantum cascade laser with a Fabry-Perot resonator, a power supply component, a temperature control component, a beam splitting component, a gas chamber to be measured, a reference gas chamber, a first photoelectric detection component, a second photoelectric detection component, and a signal processing component; The power supply component is connected to the quantum cascade laser and is used to apply a drive current to the quantum cascade laser; the temperature control component is connected to the quantum cascade laser and is used to control the heat sink temperature of the quantum cascade laser; the quantum cascade laser is connected to the beam splitting component and emits laser light to the beam splitting component; The beam splitting component is connected to the gas chamber to be measured and the reference gas chamber, and is used to split the laser beam and then emit it to the gas chamber to be measured and the reference gas chamber respectively; the first photoelectric detection component and the second detection component are respectively connected to the gas chamber to be measured and the reference gas chamber, and are used to receive the laser light passing through the gas chamber to be measured and the reference gas chamber and convert and output them into a first electrical signal and a second electrical signal; the signal processing component is connected to the first photoelectric detection component and the second photoelectric detection component, and is used to calculate the concentrations of the multiple gases based on the first electrical signal and the second electrical signal.

[0015] In a third aspect, an embodiment of the present application further provides a semiconductor laser, which is applicable to the detection method according to any of the foregoing embodiments. The semiconductor laser is a quantum cascade laser with a Fabry-Perot resonator and includes an active region that realizes diagonal transitions.

[0016] The present application can at least achieve the following beneficial effects: A method, device, and semiconductor laser for detecting multi-gas concentrations according to an embodiment of the present application employ a quantum cascade laser with a grating-free structure based on a Fabry-Perot resonator. By pre-characterizing the quantum cascade laser, the heat sink temperature and drive current are adjusted to obtain a wavelength scanning window suitable for simultaneously detecting the concentrations of multiple gases, such that the absorption peaks of the multiple gases are within the scanning range of the laser center wavelength. Then, by controlling the quantum cascade laser within a preset time of the wavelength scanning window, the laser is passed through the multiple gases to obtain a change signal of the absorption intensity of the multiple gases to the laser, and the concentrations of the multiple gases are calculated based on the change signal of the absorption intensity of the multiple gases to the laser. Thus, the embodiments of the present application can achieve rapid and accurate detection of the concentrations of multiple gases simultaneously, and due to the simple structure of the laser, the miniaturized design of the laser, low production cost, wide applicable detection range, easy adjustment, and fast detection speed, it has great application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] To more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required to be used in the embodiments of the present application. It should be understood that the following drawings only show certain embodiments of the present application and should not be regarded as limiting the scope of the present application.

[0018] Figure 1 is a schematic flowchart of a method for detecting multi-gas concentrations according to an embodiment of the present application; Figure 2 is a partial schematic flowchart of a method for detecting multi-gas concentrations according to an embodiment of the present application; Figure 3 is a partial schematic flowchart of a method for detecting multi-gas concentrations according to an embodiment of the present application; Figure 4 is a partial schematic flowchart of a method for detecting multi-gas concentrations according to an embodiment of the present application; Figure 5 is a partial schematic flowchart of a method for detecting multi-gas concentrations according to an embodiment of the present application; Figure 6 is a partial schematic flowchart of a method for detecting multi-gas concentrations according to an embodiment of the present application; Figure 7A is a schematic curve diagram of the working current of the laser according to an embodiment of the present application; Figure 7B is a schematic curve diagram of the wavelength scanning window according to an embodiment of the present application; Figure 7C is a schematic curve diagram of the first electrical signal output by the photodetector according to an embodiment of the present application; Figure 7DIt is a schematic diagram of the curve of the second electrical signal output by the photodetector according to the embodiment of the present application; Figure 8A It is an absorption spectrum curve diagram of the absorption intensities of two gases to be measured in the gas chamber to be measured varying with the central wavelength; Figure 8B It is an absorption spectrum curve diagram of the absorption intensities of three gases to be measured in the gas chamber to be measured varying with the central wavelength; Figure 9 It is a detection device for multi-gas concentration according to the embodiment of the present application; Figure 10 It is a schematic structural diagram of a semiconductor laser according to the embodiment of the present application; Figure 11 It is a schematic structural diagram of the active region of a semiconductor laser according to the embodiment of the present application. Detailed implementation manners

[0019] To make the objectives, technical solutions and advantages of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present application. However, it should be understood that the described embodiments are only some exemplary embodiments of the present application, rather than all embodiments. Therefore, the following detailed description of the embodiments of the present application is not intended to limit the scope claimed by the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope protected by the present application.

[0020] It should be noted that the terms "first", "second", etc. in the description and claims of the present application are only used to distinguish and describe similar objects, rather than to describe a specific order or sequence, nor can they be understood as indicating or implying relative importance.

[0021] As described above, the existing system for detecting gas concentration based on a distributed feedback (DFB) quantum cascade laser (QCL) uses a periodic complex grating structure and operates in a single resonant cavity mode. It mainly uses temperature change to modulate the wavelength of the laser. Since the temperature modulation coefficient of this laser for the wavelength is relatively low and the temperature control is relatively slow, it is difficult to widely adjust the wavelength range of the laser in a short time and cannot be applied to the rapid and accurate detection of the concentrations of multiple gases simultaneously. For this reason, the present application proposes a method, device and semiconductor laser for detecting multi-gas concentration. The quantum cascade laser with a grating-free structure can simultaneously perform rapid and accurate detection of the concentrations of multiple gases. Moreover, due to the simple structure of the laser, small size of the laser, low production cost and wide applicable detection range, it has great application value.

[0022] Figure 1It is a schematic flowchart of a method for detecting multiple gas concentrations according to an embodiment of the present application. As Figure 1 shown, this method can be used for a quantum cascade laser with a Fabry-Perot resonator and includes the following steps: Step S110: Pre-characterize the quantum cascade laser to obtain a wavelength scanning window suitable for detecting the concentrations of multiple gases by adjusting the heat sink temperature and drive current of the quantum cascade laser. Among them, in the wavelength scanning window, within a preset time, the laser linewidth of the quantum cascade laser is less than a first threshold, and the moving range of the laser center wavelength of the quantum cascade laser is greater than a second threshold so that the absorption peaks of the multiple gases are within the scanning range of the laser center wavelength; Step S120: Control the quantum cascade laser to pass the laser emitted by the quantum cascade laser through the multiple gases within the preset time of the wavelength scanning window, obtain a change signal of the absorption intensity of the multiple gases to the laser, and calculate the concentrations of the multiple gases based on the change signal of the absorption intensity of the multiple gases to the laser.

[0023] In this embodiment, the quantum cascade laser with a Fabry-Perot resonator has no grating structure, and the Fabry-Perot resonator is composed of two opposite parallel mirrors to form a resonator. In this structure, there is no built-in wavelength selection mechanism and it usually operates in a multi-longitudinal mode, and the output spectrum contains multiple wavelengths. In the present application, in order to achieve the single-longitudinal mode effect of a quantum cascade laser similar to that of a distributed feedback and to be able to perform wavelength modulation quickly, a diagonal transition design is made for the active region of the quantum cascade laser with a Fabry-Perot resonator. Thus, on the basis of a simpler structure and lower production cost of the quantum cascade laser with a Fabry-Perot resonator, a larger wavelength scanning range is achieved.

[0024] In step S110 of this embodiment, first pre-characterize the quantum cascade laser to obtain a wavelength scanning window suitable for simultaneously detecting the concentrations of multiple gases by adjusting the heat sink temperature and drive current. Among them, in the wavelength scanning window, the laser linewidth is less than a first threshold, and the moving range of the laser center wavelength is greater than a second threshold so that the absorption peaks of the multiple gases are within the scanning range of the laser center wavelength. Among them, the laser linewidth refers to the distribution range of the laser output spectrum in the frequency domain. The size of the linewidth directly affects the monochromaticity and coherence of the laser. The smaller the linewidth, the more concentrated the light wave output by the laser in frequency, the better the monochromaticity and coherence, and the more accurate the measurement of the absorption of light by the gas. The laser linewidth should be less than the linewidth of the gas absorption peak, and the laser linewidth can be characterized by wave number (unit cm -1 )

[0025] Specifically, by adjusting the heat sink temperature and drive current magnitude of the laser, recording the characteristics of its spectrum varying with time, a wavelength scanning window suitable for simultaneously detecting the concentrations of multiple gases to be measured is found. The wavelength scanning window can be defined as: within a predetermined time period, the laser linewidth is less than a predetermined first threshold, and the moving range of the laser central wavelength is greater than a second threshold such that the absorption peaks of the multiple gases are within the scanning range of the laser central wavelength. Within this wavelength scanning window, the central wavelength of the laser moves unidirectionally towards longer or shorter wavelengths as time increases, and the functional relationship between the laser central wavelength and time is repeatable in multiple measurements of a predetermined number of times (e.g., greater than 10 times), and its variation is less than a predetermined percentage threshold, which can be set according to the accuracy of the gas measurement concentration and is usually set to 1%. The moving range of the central wavelength affects the gas absorption range and measurement accuracy. The larger the moving range of the central wavelength, the larger the gas absorption range to be tested, the more gases can be tested, and the more accurate the measurement result.

[0026] In one embodiment, the predetermined time period of the wavelength scanning window needs to be greater than 2 μs, which is to ensure that the photodetector has sufficient sampling points and ensure the spectral accuracy of the measurement. The first threshold is expressed as 1 cm -1 , and the second threshold is 10 cm -1 , that is, the laser linewidth is less than 1 cm -1 , and the moving range of the central wavelength is greater than 10 cm -1 . Within this range, the moving range of the central wavelength can be greater than 1 / 2 of the laser gain spectrum width, satisfying the simultaneous detection of the concentrations of more than 2 gases.

[0027] In step S120 of this embodiment, the quantum cascade laser is controlled to pass the laser through the multiple gases within the preset time of the wavelength scanning window, obtain the change signal of the absorption intensity of the multiple gases to the laser, and calculate the concentrations of the multiple gases based on the change signal of the absorption intensity of the multiple gases to the laser. In one embodiment, a pulsed drive current can be applied to the quantum cascade laser and its heat sink temperature can be controlled through a temperature control component to control the quantum cascade laser to operate within the preset time of the wavelength scanning window. As Figure 7AAs shown, when a pulsed drive current is applied to the quantum cascade laser, the operating current of the laser is roughly divided into three segments in time. In the time period from 0 to tr, the current rapidly rises above the threshold current (i.e., the minimum operating current) of the laser; in the time period from tr to tf, the current slowly increases (it can increase by 10% - 15% when it is above 2 μs); after the time of tf, the current rapidly drops to 0. Therefore, a suitable wavelength scanning window exists in the time period from tr to tf, that is, the time period from tb to te, where tb and te respectively represent the start time and end time of the preset time of the wavelength scanning window. Then, the pre-characterization of the quantum cascade laser in step S110 is to characterize the time period from tb to te.

[0028] In one embodiment, the pre-characterization of the quantum cascade laser in step S110 to obtain a wavelength scanning window suitable for simultaneously detecting the concentrations of multiple gases by adjusting the heat sink temperature and the drive current includes: obtaining a first functional relationship between the laser center wavelength and time within the wavelength scanning window. Since the functional relationship between the laser center wavelength and time within this wavelength scanning window is repetitive in multiple measurements, after pre-characterization, the functional relationship between the laser center wavelength λ and time t within the time period from tb to te can be determined: 。

[0029] In one embodiment, as Figure 2 shown, the pre-characterization of the quantum cascade laser in step S110 to obtain a wavelength scanning window suitable for simultaneously detecting the concentrations of multiple gases by adjusting the heat sink temperature and the drive current of the quantum cascade laser may include the following steps: Step S210, dividing the predetermined temperature range of the heat sink temperature into N temperature intervals, dividing the predetermined current range of the drive current into M current intervals, arranging and combining the N temperature intervals and M current intervals to form experimental data of an N*M matrix, where N and M are integers greater than 1; Step S220, according to the wavelength scanning window, obtaining the target values of the heat sink temperature and the drive current that satisfy the wavelength scanning window from the experimental data of the N*M matrix.

[0030] In one embodiment, the heat sink temperature of the laser can be adjusted within a predetermined temperature range of 0 to 30 degrees Celsius, and the magnitude of the drive current can be adjusted within a range of 1 to 3 times the threshold current (i.e., the minimum operating current) of the quantum cascade laser, and the characteristics of its spectrum changing with time are recorded to find a wavelength scanning window suitable for simultaneously detecting the concentrations of multiple gases.

[0031] First, divide the temperature range of the heat sink temperature into N temperature intervals. The range of each temperature interval can be 1 to 3 degrees Celsius. The set range of the temperature interval makes it easier to control the temperature and also takes into account the measurement accuracy. Secondly, divide the current range of the drive current into M intervals. Each current interval can be 0.1 to 0.4 times the threshold current. Arrange and combine the N temperature intervals and M current intervals to form experimental data of an N*M matrix. According to the wavelength scanning window and the wavelength requirement standard of the gas absorption peak, obtain the target values of the heat sink temperature and the drive current that meet the requirements. Among them, preferably, the target value can be the data with the smallest drive current when the heat sink temperature is close to room temperature (25°C) to achieve the effect of energy saving.

[0032] In one embodiment, as Figure 3 shown, in step S120, controlling the quantum cascade laser to pass the laser emitted by the quantum cascade laser through the multiple gases within a preset time of the wavelength scanning window, obtaining a change signal of the absorption intensity of the multiple gases to the laser, and calculating the concentrations of the multiple gases based on the change signal of the absorption intensity of the multiple gases to the laser may include: Step S310, within the preset time of the wavelength scanning window, split the laser emitted by the quantum cascade laser and pass it through a reference gas chamber and a gas chamber to be measured respectively, and obtain a first current value of the intensity of the laser in the gas chamber to be measured changing with time and a second current value of the intensity of the laser in the reference gas chamber changing with time respectively; Step S320, calculate the ratio between the first current value of the intensity of the laser in the gas chamber to be measured changing with time and the second current value of the intensity of the laser in the reference gas chamber changing with time to obtain a change signal of the absorption intensity of the multiple gases in the gas chamber to be measured.

[0033] The basic principle of laser-based gas concentration detection is based on the absorption characteristics of specific gases for infrared lasers of specific wavelengths. When a laser of a predetermined wavelength passes through the gas to be measured, the gas concentration can be deduced from the change in the intensity of the laser. In this embodiment, when detecting the concentrations of multiple gases simultaneously, the laser emitted by the quantum cascade laser is split and then passes through a reference gas chamber and a gas chamber to be measured respectively. The reference gas chamber contains a reference gas, and the gas chamber to be measured contains multiple gases to be measured. The reference gas does not absorb the laser of a specific wavelength, while the gases to be measured absorb the laser of a specific wavelength. When the lasers passing through the reference gas chamber and the gas chamber to be measured are respectively received by a photodetector and converted into corresponding electrical signals, these two electrical signals respectively represent the electrical signals of the intensity of the laser in the reference gas chamber and the gas chamber to be measured changing with time. Then, by comparing and calculating these two electrical signals, the change signal of the absorption intensity of the multiple gases in the gas chamber to be measured for the laser can be calculated. Among them, the electrical signal can be a current signal.

[0034] In this embodiment, the first current value representing the intensity of the laser in the gas chamber to be measured changing with time and the second current value representing the intensity of the laser in the reference gas chamber changing with time are respectively expressed as and , then the change signal of the absorption intensity of the target gas to be measured in the gas chamber to be measured for the laser can be calculated as: .

[0035] In one embodiment, as Figure 4 shown, calculating the concentrations of the multiple gases based on the change signal of the absorption intensity of the multiple gases for the laser in step S120 may include: Step S410, based on the change signal of the absorption intensity of the multiple gases for the laser and the inverse function of the first function relationship of the laser center wavelength changing with time within the wavelength scanning window, calculate the second function relationship of the absorption intensity of the multiple gases for the laser changing with the center wavelength; Step S420, according to the second function relationship of the absorption intensity of the multiple gases for the laser changing with the center wavelength, obtain the intensity of the absorption peak of each gas in the multiple gases, and calculate the concentration of each gas according to the intensity of the absorption peak of each gas.

[0036] In this embodiment, in the foregoing pre-characterization step, the first function relationship of the laser center wavelength changing with time within the wavelength scanning window has been obtained . Thus, further based on the inverse function of the first function relationship of the laser center wavelength changing with time within the wavelength scanning window , thereby calculating a second functional relationship between the absorption intensity of the multiple gases for the laser and the change in the center wavelength, that is .

[0037] Thus, when the absorption peak of the gas to be measured is within the laser wavelength scanning range, the intensity of the absorption peak of the gas can be detected through the second functional relationship between the absorption intensity of the gas for the laser and the change in the center wavelength. Further, the concentration of each gas can be calculated based on the intensity of the absorption peak of each gas.

[0038] In one embodiment, as Figure 5 shown, in step S420, according to the second functional relationship between the absorption intensity of the multiple gases for the laser and the change in the center wavelength, obtaining the intensity of the absorption peak of each gas in the multiple gases, and calculating the concentration of each gas according to the intensity of the absorption peak of each gas includes: Step S510, obtaining the intensity of multiple absorption peaks of each gas in the multiple gases according to the second functional relationship between the absorption intensity of the multiple gases for the laser and the change in the center wavelength; Step S520, respectively calculating multiple concentration values corresponding to each gas according to the intensity of the multiple absorption peaks of each gas, and calculating the average value of the multiple concentration values as the final concentration value of each gas.

[0039] Since the gas to be measured may exhibit absorption characteristics for multiple specific wavelengths within the preset time of the wavelength scanning window, multiple absorption peaks may be detected for each gas. At this time, multiple concentration values corresponding to each gas can be calculated respectively based on the intensity of the multiple absorption peaks detected for each gas, and the average value of the multiple concentration values is calculated as the final concentration value of each gas. This can reduce the error in the detection process and further improve the reliability and accuracy of gas concentration detection.

[0040] In one embodiment, as Figure 6 shown, in step S420, according to the second functional relationship between the absorption intensity of the multiple gases for the laser and the change in the center wavelength, obtaining the intensity of the absorption peak of each gas in the multiple gases, and calculating the concentration of each gas according to the intensity of the absorption peak of each gas includes: Step S610, obtaining the intensity of multiple superimposed absorption peaks of the multiple gases according to the second functional relationship between the absorption intensity of the multiple gases for the laser and the change in the center wavelength; Step S620, constructing a system of multiple equations according to the intensity of the multiple superimposed absorption peaks and the absorption coefficients of the multiple gases involved in each superimposed absorption peak, and respectively calculating the concentration values corresponding to each gas by solving the system of equations.

[0041] Since there are multiple gases with unknown concentrations in the gas chamber to be measured, within the wavelength scanning range, it is possible that multiple gases simultaneously have absorption peaks at the same central wavelength, that is, superposed absorption peaks are formed. Then, according to the second functional relationship between the absorption intensities of the multiple gases for the laser and the change of the central wavelength, the intensities of the multiple superposed absorption peaks of the multiple gases can be obtained. A system of multiple equations is constructed based on the intensities of the multiple superposed absorption peaks and the absorption coefficients of the multiple gases involved in each superposed absorption peak, and the concentration values corresponding to each of the gases are calculated respectively by solving the system of equations.

[0042] As Figure 7B - 7D shown, when the laser is split and passed through the reference gas chamber and the gas chamber to be measured respectively within the preset time of the wavelength scanning window, assuming that the target gas to be measured shows absorption peaks at times t1 and t2 corresponding to central wavelengths λ1 and λ2 within the wavelength scanning window respectively, then according to the change curves of the electrical signals of the intensities of the laser in the reference gas chamber and the gas chamber to be measured with time, at times t1 and t2 corresponding to central wavelengths λ1 and λ2, the first electrical signal of the intensity of the laser in the gas chamber to be measured with time shows obvious descending peaks. By continuously applying a pulsed driving current to the laser, the change of the absorption peak of the gas in the gas chamber to be measured for the laser can be continuously monitored, thereby inferring the change of the gas concentration. The gas concentration can be calculated according to the Lambert-Beer law, which is a law describing the relationship between the absorption strength of a substance for monochromatic light and the concentration of the light-absorbing substance and the thickness of its liquid layer. Its mathematical expression can be represented as: A = ϵbc, where A is the absorption intensity of the gas for light, ϵ is the molar absorption coefficient, which is related to the wavelength of the incident light; b is the thickness of the absorption layer (usually in centimeters), and c is the concentration of the gas (usually in moles per liter). The above formula indicates that the absorption intensity of the gas for light is proportional to the gas concentration.

[0043] The following further elaborates on the detection principle of the embodiments of the present application in combination with Figure 8A and Figure 8B specific examples.

[0044] Example 1: Figure 8A shows the absorption spectral curves of the absorption intensities of two gases to be measured in the gas chamber to be measured with respect to the change of the central wavelength, where the central wavelength on the abscissa is characterized in wave number unit cm -1 As Figure 8A shown, the two gases to be measured are carbon monoxide (CO) and nitrous oxide (N2O). When performing gas detection, these two gases with unknown concentrations are mixed in the gas chamber to be measured. Through the pre-characterization process, the central wavelength of the laser is moved from short to long wavelengths and single-wavelength scanning is maintained. The scanning range of the wavelength can cover 2180 - 2190 cm -1Through the detection method of the above embodiment, the quantum cascade laser is controlled to split the laser beam within the preset time of the wavelength scanning window, and then pass through the reference gas chamber and the gas chamber to be tested respectively. Through the electrical signal collection and data processing calculation of the photoelectric detector, the wavelength of 2180~2190cm -1 Multiple absorption peaks were detected in the wavelength range of Figure 8A The dark blue curve in the figure is the absorption spectrum of carbon monoxide (CO), and the red curve is the absorption spectrum of nitrous oxide (N2O). It can be seen that carbon monoxide has a peak at 2183.23 cm -1 The absorption peak at is the strongest absorption peak in this scanning range (the molar absorption coefficient of carbon monoxide corresponding to this wavelength is expressed as ), the absorption intensity corresponding to this absorption peak is proportional to the gas concentration of carbon monoxide. The gas concentration of carbon monoxide can be calculated based on the absorption intensity of this absorption peak. Similarly, nitrous oxide is at 2189.26 cm -1 The absorption peak at is the strongest absorption peak in this scanning range (the molar absorption coefficient of nitrous oxide corresponding to this wavelength is expressed as ), through 2189.26 cm -1 In addition, since the wavelength tuning range of the quantum cascade laser is relatively wide, multiple absorption peaks of each of the two gases can be detected within a preset time in the wavelength scanning window, for example Figure 8A There are two strong absorption peaks for carbon monoxide and nine absorption peaks for nitrous oxide. By calculating the gas concentration for each absorption peak and averaging the results, the reliability and accuracy of the detection can be increased.

[0045] Assume that carbon monoxide is at 2183.23 cm -1 The absorption intensity at , nitrous oxide at 2189.26cm -1 The absorption intensity at , the following relationship can be obtained through the Lambert-Beer law: ; .

[0046] Where, L is the length of the gas chamber to be tested, Indicates the concentration of carbon monoxide (CO), represents the concentration of nitrous oxide (N2O). Therefore, the specific concentrations of the two gases can be obtained through the above relationship.

[0047] Example 2: Figure 8BThe absorption spectral curves showing the absorption intensities of three gases to be measured in the gas chamber to be measured varying with the central wavelength are presented. As Figure 8B shown, the three gases to be measured are formaldehyde (H2CO), nitric oxide (NO), and water vapor (H2O). When performing gas detection, these three gases with unknown concentrations are mixed in the gas chamber to be measured. Through the pre-characterization process, the central wavelength of the laser is moved from the short wavelength to the long wavelength while maintaining single-wavelength scanning, and the scanning range of the central wavelength can cover 1795 - 1805 cm -1 . After scanning, the superimposed gas absorption spectrum of the three gases can be obtained, where Figure 8B the dark blue curve is the absorption spectrum of formaldehyde (H2CO), the red curve is the absorption spectrum of nitric oxide (NO), and the light blue curve is the absorption spectrum of water vapor (H2O). First, by analyzing the gas absorption database, the absorption peaks of the three gases can be found respectively. For example, there is an absorption peak of formaldehyde at 1795.5 cm -1 (the molar absorption coefficient of formaldehyde corresponding to this wavelength is denoted as ), there is a relatively strong absorption peak of water vapor at 1801.3 cm -1 (the molar absorption coefficient of water vapor corresponding to this wavelength is denoted as ) and a relatively weak absorption peak of formaldehyde (the molar absorption coefficient of formaldehyde corresponding to this wavelength is denoted as ) (the ratio of to is about 400:1), and there are both a relatively strong absorption peak of nitric oxide at 1804.7 cm -1 (the molar absorption coefficient of nitric oxide corresponding to this wavelength is denoted as ) and a relatively weak absorption peak of formaldehyde (the molar absorption coefficient of formaldehyde corresponding to this wavelength is denoted as ) (the ratio of to is about 62:1). By extracting the absorption intensities at three positions of 1795.5 cm -1 , 1801.3 cm -1 , and 1804.7 cm -1 , which are denoted as A1, A2, and A3 respectively, the following system of multivariate equations characterizing the concentration relationship of the mixed gas can be listed: ; ; ; where L is the length of the gas chamber to be measured, represents the concentration of formaldehyde, represents the concentration of water vapor, represents the concentration of nitric oxide. Therefore, the specific concentrations of the three gases can be obtained by solving the above system of multivariate equations.

[0048] Figure 9 A detection device for multiple gas concentrations according to an embodiment of the present application is applicable to the detection method of any of the foregoing embodiments. As Figure 9 shown, the detection device includes the following components: a quantum cascade laser 710 based on a Fabry-Perot resonator, a power supply component 711, a temperature control component 712, a beam splitting component 713, a gas chamber to be measured 714, a reference gas chamber 715, a first photoelectric detection component 716, a second photoelectric detection component 717, and a signal processing component 718.

[0049] Among them, the power supply component 711 is connected to the quantum cascade laser 710 for applying a driving current to the quantum cascade laser 710. The temperature control component 712 is connected to the quantum cascade laser 710 for controlling the heat sink temperature of the quantum cascade laser 710. In one embodiment, the temperature control component 71 can include a TEC thermoelectric cooler.

[0050] The quantum cascade laser 710 is connected to the beam splitting component 713 for incident laser light on the beam splitting component 713. The beam splitting component 713 is connected to the gas chamber to be measured 714 and the reference gas chamber 715 for splitting the laser light and then respectively emitting it to the gas chamber to be measured 714 and the reference gas chamber 715. The gas chamber to be measured accommodates multiple gases with concentrations to be measured, and the reference gas chamber accommodates reference gases.

[0051] The first photoelectric detection component 716 and the second photoelectric detection component 717 are respectively connected to the gas chamber to be measured 714 and the reference gas chamber 715 for respectively receiving the laser light passing through the gas chamber to be measured 714 and the reference gas chamber 715 and converting and outputting them into a first electrical signal and a second electrical signal.

[0052] The signal processing component 718 is connected to the first photoelectric detection component 716 and the second photoelectric detection component 717 for calculating the concentrations of the multiple gases based on the first electrical signal and the second electrical signal.

[0053] Preferably, the ratio of the laser light in the gas chamber to be measured 714 and the reference gas chamber 715 is 1:1. This ratio can be the ratio of laser energy or intensity.

[0054] Figure 10 and Figure 11 A semiconductor laser 800 and a schematic structural diagram of its active region according to an embodiment of the present application are applicable to the detection method of any of the foregoing embodiments. As Figure 10 and Figure 11 shown, the semiconductor laser 800 is a quantum cascade laser based on a Fabry-Perot resonator 810 and includes an active region 820 that realizes diagonal transitions.

[0055] As Figure 11 shown, the active region 820 of the semiconductor laser 800 includes a transition region 821 and an injection region 822. In order to achieve the single longitudinal mode effect of a quantum cascade laser similar to that of a distributed feedback quantum cascade laser and enable rapid wavelength modulation, a diagonal transition design is made for the active region of the quantum cascade laser with a Fabry-Perot resonator, that is, the transition region 821 has more than two quantum wells, the upper energy level (u.l) and the lower energy level (l.l) are in adjacent quantum wells respectively, and the transition of electrons between adjacent quantum wells is in the diagonal direction. This structure enables the semiconductor laser 800 to achieve a wide gain, and the full width at half maximum of the gain can reach more than 70 cm -1 . Thus, the quantum cascade laser based on the Fabry-Perot resonator has a simpler structure and lower production cost, and can achieve a larger wavelength scanning range.

[0056] A method, device, and semiconductor laser for detecting multiple gas concentrations according to an embodiment of the present application use a quantum cascade laser with a grating-free structure having a Fabry-Perot resonator. By pre-characterizing the quantum cascade laser, the heat sink temperature and drive current are adjusted to obtain a wavelength scanning window suitable for simultaneously detecting the concentrations of multiple gases, so that the absorption peaks of the multiple gases are within the scanning range of the laser center wavelength. Then, by controlling the quantum cascade laser within a preset time of the wavelength scanning window, the laser is passed through the multiple gases to obtain a change signal of the absorption intensity of the multiple gases to the laser, and the concentrations of the multiple gases are calculated based on the change signal of the absorption intensity of the multiple gases to the laser. Thus, the embodiment of the present application can achieve rapid and accurate detection of the concentrations of multiple gases simultaneously, and due to the simple structure of the laser, low production cost, and wide applicable detection range, it has great application value.

[0057] It should be noted that those skilled in the art can understand that the different implementation manners, explanations, and achieved technical effects described in the method embodiments of the present application are equally applicable to the device embodiments of the present application, and will not be repeated here.

[0058] The above describes exemplary embodiments of the present application. It should be understood that the above exemplary embodiments are not restrictive but illustrative, and the protection scope of the present application is not limited thereto. It should be understood that those skilled in the art can modify and vary the embodiments of the present application without departing from the spirit and scope of the present application, and these modifications and variations should reasonably fall within the protection scope of the present application.

Claims

1. A detection method for multi-gas concentrations, applicable to a quantum cascade laser with a Fabry-Perot resonator, characterized in that, The method includes: Pre-characterizing the quantum cascade laser to obtain a wavelength scanning window suitable for detecting the concentrations of multiple gases by adjusting the heat sink temperature and driving current of the quantum cascade laser. In the wavelength scanning window, within a preset time, the laser linewidth of the quantum cascade laser is less than a first threshold, and the moving range of the laser center wavelength of the quantum cascade laser is greater than a second threshold so that the absorption peaks of the multiple gases are within the scanning range of the laser center wavelength; Controlling the quantum cascade laser to pass the laser emitted by the quantum cascade laser through the multiple gases within the preset time of the wavelength scanning window, obtaining a change signal of the absorption intensity of the multiple gases to the laser, and calculating the concentrations of the multiple gases based on the change signal of the absorption intensity of the multiple gases to the laser.

2. The detection method for multi-gas concentration according to claim 1, characterized in that, The pre-characterizing the quantum cascade laser to obtain a wavelength scanning window suitable for simultaneously detecting the concentrations of multiple gases by adjusting the heat sink temperature and driving current of the quantum cascade laser includes: Dividing the predetermined temperature range of the heat sink temperature into N temperature intervals, dividing the predetermined current range of the driving current into M current intervals, arranging and combining the N temperature intervals and M current intervals to form experimental data of an N*M matrix, where N and M are integers greater than 1; According to the wavelength scanning window, obtaining target values of the heat sink temperature and driving current that satisfy the wavelength scanning window from the experimental data of the N*M matrix.

3. The detection method for multi-gas concentration according to claim 1, characterized in that, Pre-characterizing the quantum cascade laser to obtain a wavelength scanning window suitable for detecting the concentrations of multiple gases by adjusting the heat sink temperature and drive current of the quantum cascade laser includes: obtaining a first functional relationship between the laser center wavelength and time within the wavelength scanning window, and the first functional relationship is , where λ is the laser center wavelength, t is the preset time of the wavelength scanning window, and tb and te respectively represent the start time and end time of the preset time of the wavelength scanning window.

4. The detection method for multi-gas concentration according to claim 3, characterized in that, Within the wavelength scanning window, the central wavelength of the laser moves unidirectionally towards a longer wavelength or a shorter wavelength as time increases, and the first functional relationship is repeatable in multiple measurements exceeding a predetermined number of times, and the change in the central wavelength is less than a predetermined percentage threshold.

5. The detection method for multi-gas concentration according to claim 4, characterized in that, The controlling the quantum cascade laser to pass the laser emitted by the quantum cascade laser through the multiple gases within the preset time of the wavelength scanning window, obtaining a change signal of the absorption intensity of the multiple gases to the laser, includes: Within the preset time of the wavelength scanning window, splitting the laser emitted by the quantum cascade laser and passing it through a reference gas chamber and a gas chamber to be measured respectively, and obtaining a first current value of the intensity of the laser in the gas chamber to be measured changing with time and a second current value of the intensity of the laser in the reference gas chamber changing with time respectively; Calculate a first current value of the intensity of the laser varying with time in the gas chamber to be measured and a second current value of the intensity of the laser varying with time in the reference gas chamber to obtain a change signal of the absorption intensity of the multiple gases in the gas chamber to be measured with respect to the laser , where .

6. The detection method for multi-gas concentration according to claim 5, characterized in that, The calculating the concentrations of the multiple gases based on the change signal of the absorption intensity of the multiple gases to the laser includes: Based on and the first functional relationship the inverse function calculate the second functional relationship of the absorption intensity of the multiple gases for the laser varying with the central wavelength , ; According to the second functional relationship between the absorption intensity of the multiple gases for the laser and the change of the central wavelength , obtain the intensity of the absorption peak of each gas among the multiple gases, and calculate the concentration of each gas according to the intensity of the absorption peak of each gas.

7. The detection method for multi-gas concentration according to claim 6, wherein The second functional relationship of the absorption intensity of the multiple gases with respect to the laser varying with the central wavelength , obtaining the intensity of the absorption peak of each gas in the multiple gases, and calculating the concentration of each gas according to the intensity of the absorption peak of each gas includes: According to the second functional relationship between the absorption intensity of the multiple gases for the laser and the change of the central wavelength , obtain the intensities of multiple absorption peaks of each gas among the multiple gases; Calculating multiple concentration values corresponding to each gas according to the intensities of multiple absorption peaks of each gas respectively, and calculating the average value of the multiple concentration values as the final concentration value of each gas.

8. The detection method of multi-gas concentration according to claim 6, wherein, The second functional relationship between the absorption intensity of the various gases for the laser and the change in the central wavelength , obtaining the intensity of the absorption peak of each gas among the various gases, and calculating the concentration of each gas according to the intensity of the absorption peak of each gas includes: According to the second functional relationship between the absorption intensity of the multiple gases for the laser and the change of the central wavelength , obtain the intensities of multiple superimposed absorption peaks of the multiple gases; Constructing a system of multiple equations based on the intensities of the multiple superimposed absorption peaks and the absorption coefficients of the multiple gases involved in each superimposed absorption peak, and calculating the concentration values corresponding to each gas respectively by solving the system of multiple equations.

9. The detection method for multi-gas concentration according to claim 1, characterized in that The first threshold is 1 cm -1 , and the second threshold is 10 cm -1 .

10. The detection method for multi-gas concentration according to claim 2, wherein The predetermined temperature range of the heat sink temperature is 0 to 30 degrees Celsius, the predetermined current range of the driving current is 1 to 3 times the threshold current of the quantum cascade laser, the range of each temperature interval is 1 to 3 degrees Celsius, and the range of the current interval is 0.1 to 0.4 times the threshold current.

11. A detection device for multi-gas concentration, applicable to the detection method according to any one of claims 1-10, characterized in that, including: A quantum cascade laser with a Fabry-Perot resonator, a power supply component, a temperature control component, a beam splitting component, a gas chamber to be measured, a reference gas chamber, a first photoelectric detection component, a second photoelectric detection component, and a signal processing component; The power supply component is connected to the quantum cascade laser and is used to apply a driving current to the quantum cascade laser; The temperature control component is connected to the quantum cascade laser and is used to control the heat sink temperature of the quantum cascade laser; The quantum cascade laser is connected to the beam splitting component and emits laser light to the beam splitting component; The beam splitting component is connected to the gas chamber to be measured and the reference gas chamber and is used to split the laser beam and then emit it to the gas chamber to be measured and the reference gas chamber respectively; the first photoelectric detection component and the second detection component are respectively connected to the gas chamber to be measured and the reference gas chamber and are used to receive the laser light passing through the gas chamber to be measured and the reference gas chamber and convert and output them into a first electrical signal and a second electrical signal; the signal processing component is connected to the first photoelectric detection component and the second photoelectric detection component and is used to calculate the concentrations of the multiple gases based on the first electrical signal and the second electrical signal.

12. A semiconductor laser applicable to the detection method according to any one of claims 1-10, characterized in that The semiconductor laser is a quantum cascade laser with a Fabry-Perot resonator and includes an active region that realizes diagonal transitions.

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