Multi-gas concentration detection method, device and semiconductor laser

Abstract

The present application discloses a method, device, and semiconductor laser for detecting the concentration of multiple gases, belonging to the field of gas detection technology. The method employs a grating-free quantum cascade laser with a Fabry-Perot resonant cavity. The method pre-characterizes the quantum cascade laser and adjusts the heat sink temperature and drive current 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's center wavelength. The method then controls the quantum cascade laser to pass through the multiple gases within a preset time within the wavelength scanning window, obtaining signals indicating changes in the absorption intensity of the multiple gases. Based on these signals, the concentrations of the multiple gases are calculated. The method can achieve rapid and accurate simultaneous detection of the concentrations of multiple gases, has a simple structure, low production cost, a wide range of applicable detection, and great application value.

Description

Technical Field

[0001] The present application relates to the technical field of gas detection based on semiconductor lasers, and in particular to a method and device for detecting multiple gas concentrations and a semiconductor laser. Background Art

[0002] In some gas detection application scenarios, such as respiratory monitoring and chemical reaction monitoring, it is necessary to continuously and rapidly monitor the changes in the concentration components of multiple gases to be tested. The existing distributed feedback (DFB)-based quantum cascade laser (QCL) gas concentration detection system uses a complex distributed feedback grating structure and operates in a single resonant cavity mode. This structure requires additional high-precision photolithography process steps, is costly, and has yield issues. In addition, the distributed feedback grating structure mainly uses temperature changes to modulate the wavelength of the laser. Since the temperature modulation coefficient of this laser on the wavelength is low, the temperature control is relatively slow, making it difficult to adjust the wavelength range of the laser over a large range in a short period of time. It is not suitable for the rapid and accurate detection of the concentration of multiple gases at the same time. 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 proposes a method, device and semiconductor laser for detecting the concentration of multiple gases. By using a quantum cascade laser without a grating structure, the concentrations of multiple gases can be quickly and accurately detected at the same time. Moreover, due to the simple structure of the laser, low production cost, and wide applicable detection range, it has great application value.

[0004] In a first aspect, embodiments of the present application provide a method for detecting multi-gas concentrations, applicable to a quantum cascade laser having a Fabry-Perot cavity, the method comprising:

[0005] Pre-characterizing the quantum cascade laser, and obtaining 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, wherein within a preset time, within the wavelength scanning window, the laser linewidth of the quantum cascade laser is less than a first threshold, and the movement 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;

[0006] The quantum cascade laser is controlled to pass the laser light emitted by the quantum cascade laser through the multiple gases within a preset time in the wavelength scanning window, thereby obtaining a change signal of the absorption intensity of the multiple gases to the laser light, and calculating the concentration of the multiple gases based on the change signal of the absorption intensity of the multiple gases to the laser light.

[0007] Optionally, the pre-characterizing the quantum cascade laser and obtaining 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:

[0008] 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, and arranging and combining the N temperature intervals and the M current intervals to form experimental data of an N*M matrix, where N and M are integers greater than 1;

[0009] According to the wavelength scanning window, target values ​​of the heat sink temperature and the driving current that meet the wavelength scanning window are obtained from the experimental data of the N*M matrix.

[0010] Optionally, the pre-characterization of the quantum cascade laser and obtaining 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 include: obtaining a first functional relationship of the laser center wavelength in the wavelength scanning window versus time, wherein the first functional relationship is: , where λ is the laser center wavelength, t is the preset time of the wavelength scanning window, tb and te represent the start time and end time of the preset time of the wavelength scanning window respectively.

[0011] Optionally, within the wavelength scanning window, the central wavelength of the laser moves unidirectionally toward a longer wavelength or a shorter wavelength as time increases, and the first functional relationship The central wavelength is repeatable over a plurality of measurements exceeding a predetermined number of times and varies by less than a predetermined percentage threshold.

[0012] Optionally, controlling the quantum cascade laser to pass the laser light emitted by the quantum cascade laser through the multiple gases within a preset time in the wavelength scanning window to obtain a change signal of absorption intensity of the laser light by the multiple gases includes:

[0013] Within a preset time of the wavelength scanning window, the laser light emitted by the quantum cascade laser is split and then passed through a reference gas chamber and a test gas chamber respectively, thereby obtaining a first current value of the laser light intensity in the test gas chamber and a second current value of the laser light intensity in the reference gas chamber as a function of time;

[0014] Calculate the first current value of the laser intensity in the gas chamber to be measured that changes with time The second current value of the laser intensity in the reference gas chamber changes with time to obtain a change signal of the absorption intensity of the laser by the multiple gases in the gas chamber to be measured. ,in, .

[0015] Optionally, calculating the concentrations of the multiple gases based on the change signals of the absorption intensities of the multiple gases to the laser light includes:

[0016] based on And the first functional relationship The inverse function of , calculate the second functional relationship between the absorption intensity of the multiple gases for the laser and the central wavelength , ;

[0017] According to the second functional relationship between the absorption intensity of the multiple gases for the laser and 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.

[0018] Optionally, the second functional relationship between the absorption intensity of the multiple gases for the laser and the central wavelength is , obtaining the intensity of the absorption peak of each gas in the plurality of gases, and calculating the concentration of each gas according to the intensity of the absorption peak of each gas includes:

[0019] According to the second functional relationship between the absorption intensity of the multiple gases for the laser and the central wavelength , obtaining the intensities of a plurality of absorption peaks of each of the plurality of gases;

[0020] A plurality of concentration values ​​corresponding to each gas are calculated according to the intensities of the plurality of absorption peaks of each gas, and an average value of the plurality of concentration values ​​is calculated as the final concentration value of each gas.

[0021] Optionally, the second functional relationship between the absorption intensity of the multiple gases for the laser and the central wavelength is , obtaining the intensity of the absorption peak of each gas in the plurality of gases, and calculating the concentration of each gas according to the intensity of the absorption peak of each gas includes:

[0022] According to the second functional relationship between the absorption intensity of the multiple gases for the laser and the central wavelength , obtaining the intensities of the multiple superimposed absorption peaks of the multiple gases;

[0023] A multivariate equation group is constructed 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 the concentration value corresponding to each gas is calculated by solving the multivariate equation group.

[0024] Optionally, the first threshold is 1 cm -1 , the second threshold is 10 cm -1 .

[0025] Optionally, 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.

[0026] 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 aforementioned embodiments, comprising: a quantum cascade laser having a Fabry-Perot resonant cavity, a power supply component, a temperature control component, a spectroscopic 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;

[0027] 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 light splitting component and is used to inject laser light into the light splitting component;

[0028] The spectroscopic component is connected to the gas chamber to be measured and the reference gas chamber, and is used to split the laser and 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 respectively receive the laser passing through the gas chamber to be measured and the reference gas chamber and convert the output 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.

[0029] In a third aspect, an embodiment of the present application further proposes a semiconductor laser suitable for the detection method described in any of the aforementioned embodiments, wherein the semiconductor laser is a quantum cascade laser having a Fabry-Perot cavity, including an active region that realizes diagonal transitions.

[0030] The present application can achieve at least the following beneficial effects: a method, device, and semiconductor laser for detecting the concentration of multiple gases in an embodiment of the present application utilizes a grating-free quantum cascade laser based on a Fabry-Perot resonator. By pre-characterizing the quantum cascade laser and adjusting the heat sink temperature and drive current 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's center wavelength, the quantum cascade laser is then controlled to pass through the multiple gases within a preset time within the wavelength scanning window, obtaining signals indicating changes in the absorption intensity of the multiple gases, and calculating the concentrations of the multiple gases based on the signals indicating changes in the absorption intensity of the multiple gases. Thus, the embodiments of the present application can achieve rapid and accurate simultaneous detection of the concentrations of multiple gases. Furthermore, due to the simple laser structure and miniaturized laser design, the production cost is low, the detection range is wide, the adjustment is convenient, and the detection speed is fast, thus having great application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. It should be understood that the following drawings only illustrate certain embodiments of the present application and should not be regarded as limiting the scope of the present application.

[0032] Figure 1 is a flow chart of a method for detecting multiple gas concentrations according to an embodiment of the present application;

[0033] Figure 2 1 is a partial flow chart of a method for detecting multiple gas concentrations according to an embodiment of the present application;

[0034] Figure 3 1 is a partial flow chart of a method for detecting multiple gas concentrations according to an embodiment of the present application;

[0035] Figure 4 1 is a partial flow chart of a method for detecting multiple gas concentrations according to an embodiment of the present application;

[0036] Figure 5 1 is a partial flow chart of a method for detecting multiple gas concentrations according to an embodiment of the present application;

[0037] Figure 6 1 is a partial flow chart of a method for detecting multiple gas concentrations according to an embodiment of the present application;

[0038] Figure 7A is a schematic diagram of a curve of a laser operating current according to an embodiment of the present application;

[0039] Figure 7Bis a schematic diagram of a wavelength scanning window according to an embodiment of the present application;

[0040] Figure 7C is a schematic diagram of a curve of a first electrical signal output by a photodetector according to an embodiment of the present application;

[0041] Figure 7D is a schematic diagram of a curve of a second electrical signal output by a photodetector according to an embodiment of the present application;

[0042] Figure 8A It is an absorption spectrum curve diagram showing the absorption intensity of the laser by the two gases to be tested in the gas chamber to be tested as the central wavelength changes;

[0043] Figure 8B It is an absorption spectrum curve diagram showing the absorption intensity of the laser by the three gases in the gas chamber to be tested changing with the central wavelength;

[0044] Figure 9 A multi-gas concentration detection device according to an embodiment of the present application;

[0045] Figure 10 is a schematic structural diagram of a semiconductor laser according to an embodiment of the present application;

[0046] Figure 11 Schematic diagram of the structure of the active region of a semiconductor laser according to an embodiment of the present application. DETAILED DESCRIPTION

[0047] In order to make the purpose, 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 in conjunction with the 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, not all embodiments, and therefore the following detailed description of the embodiments of the present application is not intended to limit the scope of protection claimed in this application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of this application.

[0048] It should be noted that the terms "first", "second", etc. in the description and claims of this application are only used to distinguish and describe similar objects, rather than to describe a specific order or sequence, and cannot be understood as indicating or implying relative importance.

[0049] As previously mentioned, existing distributed feedback (DFB)-based quantum cascade laser (QCL) gas concentration detection systems use a periodic complex grating structure and operate in a single-resonant cavity mode, primarily using temperature changes to modulate the laser wavelength. Due to the low wavelength modulation coefficient of temperature in such lasers, temperature control is relatively slow, making it difficult to adjust the laser wavelength range over a large range in a short period of time. This makes it unsuitable for rapid and accurate detection of the concentrations of multiple gases simultaneously. To this end, this application proposes a multi-gas concentration detection method, device, and semiconductor laser using a grating-free quantum cascade laser that can rapidly and accurately detect the concentrations of multiple gases simultaneously. Furthermore, due to the simple laser structure, small laser size, and low production cost, the method has a wide applicable detection range and great application value.

[0050] Figure 1 FIG. 1 is a flow chart of a method for detecting multiple gas concentrations according to an embodiment of the present application. Figure 1 As shown, the method can be used for a quantum cascade laser with a Fabry-Perot cavity, comprising the following steps:

[0051] Step S110, pre-characterizing the quantum cascade laser, and obtaining 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, wherein within 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;

[0052] Step S120: Control the quantum cascade laser to pass the laser light emitted by the quantum cascade laser through the multiple gases within a preset time in the wavelength scanning window, obtain a change signal of the absorption intensity of the multiple gases to the laser light, and calculate the concentration of the multiple gases based on the change signal of the absorption intensity of the multiple gases to the laser light.

[0053] In this embodiment, the quantum cascade laser with a Fabry-Perot resonant cavity does not have a grating structure, and the Fabry-Perot resonant cavity uses two opposing parallel mirrors to form a resonant cavity. In this structure, there is no built-in wavelength selection mechanism, and it usually works in a multi-longitudinal mode, and the output spectrum contains multiple wavelengths. In this application, in order to achieve a single longitudinal mode effect similar to a distributed feedback quantum cascade laser and to be able to quickly modulate the wavelength, a diagonal transition design is made for the active region of the quantum cascade laser of the Fabry-Perot resonant cavity. Thus, on the basis of the simpler structure and lower production cost of the quantum cascade laser with a Fabry-Perot resonant cavity, a wavelength scanning range with a wider coverage is achieved.

[0054] In step S110 of this embodiment, the quantum cascade laser is first pre-characterized, and a wavelength scanning window suitable for simultaneously detecting the concentrations of multiple gases is obtained by adjusting the heat sink temperature and the driving current, wherein in the wavelength scanning window, the laser line width is less than a first threshold value, and the moving range of the laser center wavelength is greater than a second threshold value so that the absorption peaks of the multiple gases are within the scanning range of the laser center wavelength. The laser line width refers to the distribution range of the laser output spectrum in the frequency domain. The size of the line width directly affects the monochromaticity and coherence of the laser. The smaller the line width, the more concentrated the light wave output by the laser is in frequency, the better the monochromaticity and coherence are, and the more accurate the measurement of the gas's absorption of light. The laser line width should be smaller than the line width of the gas absorption peak. The laser line width can be expressed in wave numbers (unit: cm -1 ) to characterize.

[0055] Specifically, by adjusting the laser's heat sink temperature and drive current, and recording the temporal characteristics of its spectrum, a wavelength scanning window suitable for simultaneously detecting the concentrations of multiple gases to be measured is identified. This wavelength scanning window can be defined as an operating window within a predetermined time period where the laser linewidth is less than a predetermined first threshold and the range of the laser's center wavelength shifts greater than a second threshold, ensuring that the absorption peaks of the multiple gases are within the scanning range of the laser's center wavelength. Within this wavelength scanning window, the laser's center wavelength shifts unidirectionally toward longer or shorter wavelengths over time. The time-dependent relationship between the laser's center wavelength and measurement is repeatable over a predetermined number of measurements (e.g., greater than 10), with the variation less than a predetermined percentage threshold. This percentage threshold can be set based on the accuracy of the gas concentration measurement and is typically set to 1%. The center wavelength's range of motion affects the measured gas absorption range and measurement accuracy. A larger center wavelength range broadens the gas absorption range, allowing for more gases to be tested and resulting in more accurate measurement results.

[0056] In one embodiment, the predetermined time period of the wavelength scanning window needs to be greater than 2㎲, in order to ensure that the photodetector has enough sampling points and the spectral accuracy of the measurement is guaranteed. The first threshold is expressed as 1 cm -1 , the second threshold is 10 cm -1 , that is, the laser line width is less than 1 cm -1 , the range of central wavelength movement is greater than 10 cm -1 Within this range, the movement range of the central wavelength can be greater than 1 / 2 of the laser gain spectrum width, which meets the requirements for simultaneous detection of the concentrations of more than two gases.

[0057] 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, and a change signal of the absorption intensity of the multiple gases to the laser is obtained, and the concentration of the multiple gases is calculated based on the change signal of the absorption intensity of the multiple gases to the laser. In one embodiment, a pulsed driving current can be applied to the quantum cascade laser and its heat sink temperature can be controlled by a temperature control component to control the quantum cascade laser to operate within the preset time of the wavelength scanning window. Figure 7A As shown, when a pulsed drive current is applied to the quantum cascade laser, the laser's operating current is roughly divided into three time periods. During the time period from 0 to tr, the current rapidly rises to above the laser's threshold current (i.e., the minimum operating current); during the time period from tr to tf, the current slowly increases (by 10% to 15% for periods above 2㎲); and after tf, the current rapidly drops to zero. Therefore, the appropriate wavelength scanning window exists within the time period from tr to tf, i.e., the time period from tb to te, where tb and te represent the start and end times of the preset wavelength scanning window, respectively. Therefore, the pre-characterization of the quantum cascade laser in step S110 is intended to characterize this time period from tb to te.

[0058] In one embodiment, pre-characterizing 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 drive current includes obtaining a first functional relationship of the laser center wavelength varying with time within the wavelength scanning window. Because the functional relationship of the laser center wavelength varying with time within the wavelength scanning window is reproducible across multiple measurements, after pre-characterization, the functional relationship of the laser center wavelength λ varying with time t within the time period tb to te can be determined: .

[0059] In one embodiment, Figure 2 As shown, the step S110 of pre-characterizing the quantum cascade laser and adjusting the heat sink temperature and driving current of the quantum cascade laser to obtain a wavelength scanning window suitable for simultaneously detecting the concentrations of multiple gases may include the following steps:

[0060] 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, and arranging and combining the N temperature intervals and the M current intervals to form experimental data of an N*M matrix, where N and M are integers greater than 1;

[0061] Step S220 , according to the wavelength scanning window, obtaining target values ​​of the heat sink temperature and the driving current that meet the wavelength scanning window from the experimental data of the N*M matrix.

[0062] 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 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. The characteristics of its spectrum changing over time are recorded to find a wavelength scanning window suitable for simultaneously detecting the concentrations of multiple gases.

[0063] First, the temperature range of the heat sink is divided into N temperature intervals. Each temperature interval can range from 1 to 3 degrees Celsius. The range of the temperature interval setting makes it easier to control the temperature while also considering the accuracy of the measurement.

[0064] Next, the drive current range is divided into M intervals, each of which can be 0.1 to 0.4 times the threshold current. These N temperature intervals and M current intervals are permuted and combined to form an N*M matrix of experimental data. Based on the wavelength scanning window and the wavelength requirements of the gas absorption peak, target values ​​for the heat sink temperature and drive current that meet the requirements are obtained. Preferably, the target value is the data at which the drive current is minimized when the heat sink temperature is close to room temperature (25°C) to achieve energy savings.

[0065] In one embodiment, Figure 3 As shown, in step S120, controlling the quantum cascade laser to pass the laser light emitted by the quantum cascade laser through the multiple gases within a preset time in the wavelength scanning window, obtaining signals of changes in absorption intensities of the multiple gases to the laser light, and calculating the concentrations of the multiple gases based on the signals of changes in absorption intensities of the multiple gases to the laser light may include:

[0066] Step S310, within a preset time of the wavelength scanning window, splitting the laser light emitted by the quantum cascade laser and passing it through a reference gas chamber and a test gas chamber, respectively, to obtain a first current value of the laser light intensity in the test gas chamber and a second current value of the laser light intensity in the reference gas chamber as a function of time;

[0067] Step S320, calculating the ratio between the first current value of the laser intensity in the gas chamber to be tested and the second current value of the laser intensity in the reference gas chamber to be tested, so as to obtain a change signal of the absorption intensity of the laser by the multiple gases in the gas chamber to be tested.

[0068] The basic principle of laser-based gas concentration detection is based on the absorption characteristics of specific gases for infrared laser light of a specific wavelength. When laser light of a predetermined wavelength passes through the gas to be measured, the gas concentration can be inferred from the change in laser intensity. In this embodiment, when simultaneously measuring the concentration of multiple gases, the laser light emitted by the quantum cascade laser is split and then passed through a reference gas chamber and a test gas chamber. The reference gas chamber contains a reference gas, while the test gas chamber contains multiple test gases. The reference gas does not absorb laser light of a specific wavelength, while the test gases do absorb laser light of a specific wavelength. The laser light passing through the reference gas chamber and the test gas chamber is received by photodetectors and converted into corresponding electrical signals. These two electrical signals represent the temporal variation of the laser light intensity in the reference and test gas chambers, respectively. By comparing these two electrical signals, the variation in the laser light absorption intensity of the multiple gases in the test gas chamber can be calculated. These electrical signals can be current signals.

[0069] In this embodiment, the first current value of the laser intensity in the test chamber that changes with time and the second current value of the laser intensity in the reference chamber that changes with time are 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 is It can be calculated as: .

[0070] In one embodiment, Figure 4 As shown, the calculation of the concentrations of the multiple gases based on the change signals of the absorption intensities of the multiple gases to the laser in step S120 may include:

[0071] Step S410, calculating a second functional relationship between the absorption intensity of the multiple gases for the laser and the central wavelength based on the change signals of the absorption intensity of the multiple gases for the laser and the inverse function of the first functional relationship between the central wavelength of the laser and time within the wavelength scanning window;

[0072] Step S420 , obtaining the intensity of the absorption peak of each of the multiple gases according to a second functional relationship between the absorption intensity of the multiple gases for laser light and the central wavelength, and calculating the concentration of each gas according to the intensity of the absorption peak of each gas.

[0073] In this embodiment, in the aforementioned pre-characterization step, a first functional relationship of the laser center wavelength changing with time within the wavelength scanning window has been obtained. Thus, it is possible to further calculate the inverse function of the first functional relationship of the laser center wavelength varying with time within the wavelength scanning window. , thereby calculating the second functional relationship between the absorption intensity of the multiple gases for the laser and the central wavelength, that is, .

[0074] Therefore, when the gas to be measured has an absorption peak within the laser wavelength scanning range, the intensity of the gas absorption peak can be detected through the second functional relationship in which the absorption intensity of the gas to the laser changes with the central wavelength, and the concentration of each gas can be further calculated based on the intensity of the absorption peak of each gas.

[0075] In one embodiment, Figure 5 As shown, in step S420, obtaining the intensity of the absorption peak of each of the multiple gases according to the second functional relationship between the absorption intensity of the multiple gases for the laser and the central wavelength, and calculating the concentration of each gas according to the intensity of the absorption peak of each gas includes:

[0076] Step S510, obtaining the intensities of multiple absorption peaks of each of the multiple gases according to a second functional relationship between the absorption intensities of the multiple gases for laser light and the central wavelength;

[0077] In step S520 , a plurality of concentration values ​​corresponding to each gas are calculated according to the intensities of the plurality of absorption peaks of each gas, and an average value of the plurality of concentration values ​​is calculated as a final concentration value of each gas.

[0078] Since the gas to be measured may exhibit absorption characteristics at 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 based on the intensities of the multiple absorption peaks detected for each gas, and the average value of the multiple concentration values ​​can be calculated as the final concentration value of each gas. This can reduce errors in the detection process and further improve the reliability and accuracy of gas concentration detection.

[0079] In one embodiment, Figure 6 As shown, in step S420, obtaining the intensity of the absorption peak of each of the multiple gases according to the second functional relationship between the absorption intensity of the multiple gases for the laser and the central wavelength, and calculating the concentration of each gas according to the intensity of the absorption peak of each gas includes:

[0080] Step S610, obtaining intensities of a plurality of superimposed absorption peaks of the plurality of gases according to a second functional relationship between the absorption intensities of the plurality of gases for laser light and the central wavelength;

[0081] Step S620 , constructing a multivariate equation group 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 calculating the concentration value corresponding to each gas by solving the multivariate equation group.

[0082] Since multiple gases of unknown concentrations are mixed in the gas chamber to be tested, it is possible that multiple gases may have absorption peaks at the same central wavelength within the wavelength scanning range, that is, superimposed absorption peaks. In this case, the intensities of the multiple superimposed absorption peaks of the multiple gases can be obtained based on a second functional relationship in which the absorption intensity of the multiple gases for laser light varies with the central wavelength. A multivariate equation group is constructed based on the intensities of the multiple superimposed absorption peaks and the absorption coefficients of the multiple gases involved in each superimposed absorption peak. The concentration values ​​corresponding to each gas can be calculated by solving the multivariate equation group.

[0083] like Figures 7B-7D As shown, within the preset time of the wavelength scanning window, the laser beam is split and passed through the reference gas chamber and the test gas chamber, respectively. Assuming that the target gas to be tested exhibits absorption peaks at times t1 and t2 corresponding to the center wavelengths λ1 and λ2 within the wavelength scanning window, respectively, then according to the curves of the time-varying electrical signals of the laser intensity in the reference and test gas chambers, at times t1 and t2 corresponding to the center wavelengths λ1 and λ2, the first electrical signal of the time-varying laser intensity in the test gas chamber exhibits a significantly decreasing peak value. By continuously applying a pulsed drive current to the laser, the changes in the laser absorption peak of the gas in the test gas chamber can be continuously monitored, thereby inferring changes in gas concentration. Gas concentration can be calculated using the Lambert-Beer law, which describes the relationship between the strength of a substance's absorption of monochromatic light and the concentration of the absorbing substance and the thickness of its liquid layer. Its mathematical expression can be expressed as: A=ϵbc, where A is the gas's absorption intensity of 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 shows that the gas's absorption intensity of light is proportional to the gas concentration.

[0084] The following combination Figure 8A and Figure 8B The specific examples further illustrate the detection principle of the embodiments of the present application.

[0085] Example 1:

[0086] Figure 8A The absorption spectrum curve of the two gases to be tested in the gas chamber to be tested is shown as the absorption intensity of the laser changes with the central wavelength, where the central wavelength of the horizontal axis is in wave number units of cm -1 Characterization. Figure 8AAs shown in the figure, the two gases to be tested are carbon monoxide (CO) and nitrous oxide (N2O). When performing gas detection, these two gases of unknown concentration are mixed in the gas chamber to be tested. Through the pre-characterization process, the center wavelength of the laser is shifted from short to long wavelength, and a single wavelength scan is maintained. The wavelength scanning range can cover 2180~2190cm -1 By using 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. By collecting the electrical signal of the photoelectric detector and processing the data, the wavelength between 2180 and 2190 cm -1 Multiple absorption peaks were detected in the wavelength range of Figure 8A The dark blue curve 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 high absorption spectrum 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 The absorption intensity at the position can also be used to calculate the gas concentration of nitrous oxide. In addition, since the wavelength tuning range of the quantum cascade laser is wide, multiple absorption peaks of each of the two gases can be detected within the preset time of 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.

[0087] 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:

[0088] ;

[0089] .

[0090] Wherein, L is the length of the gas chamber to be measured, 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.

[0091] Example 2:

[0092] Figure 8B The absorption spectrum curves of the three gases to be tested in the test chamber show the absorption intensity of the laser as the central wavelength changes. Figure 8B As shown in the figure, the three gases to be tested are formaldehyde (H2CO), nitric oxide (NO), and water vapor (H2O). When performing gas detection, these three gases of unknown concentration are mixed in the test chamber. Through the pre-characterization process, the center wavelength of the laser is shifted from short to long wavelength, while maintaining a single wavelength scan. The center wavelength scan range can cover 1795~1805cm -1 After scanning, the superimposed gas absorption spectrum of the three gases can be obtained, among which 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, we can find the absorption peaks of the three gases, such as 1795.5cm -1 There is an absorption peak of formaldehyde at (the molar absorption coefficient of formaldehyde corresponding to this wavelength is expressed as ), 1801.3cm -1 There is a strong absorption peak of water vapor at (the molar absorption coefficient of water vapor corresponding to this wavelength is expressed as ) and a weaker absorption peak of formaldehyde (the molar absorption coefficient of formaldehyde corresponding to this wavelength is expressed as )( and The ratio is about 400:1), 1804.7cm -1 There is also a strong absorption peak of nitric oxide at this wavelength (the molar absorption coefficient of nitric oxide corresponding to this wavelength is expressed as ) and a weaker absorption peak of formaldehyde (the molar absorption coefficient of formaldehyde corresponding to this wavelength is expressed as )( and The ratio is about 62:1), by extracting the superimposed absorption peak at 1795.5 cm -1 , 1801.3cm -1 , 1804.7cm -1 The absorption intensities at the three positions are expressed as A1, A2, and A3, respectively. The multivariate equations that characterize the concentration relationship of the mixed gas can be listed as follows:

[0093] ;

[0094] ;

[0095] ;

[0096] Wherein, L is the length of the gas chamber to be measured, Indicates the concentration of formaldehyde, Indicates the concentration of water vapor, represents the concentration of nitric oxide. Therefore, by solving the above multivariate equations, the specific concentrations of the three gases can be obtained.

[0097] Figure 9 This is a multi-gas concentration detection device according to an embodiment of the present application, which is applicable to the detection method of any of the above embodiments. Figure 9 As shown, the detection device includes the following components: a quantum cascade laser 710 based on a Fabry-Perot cavity, a power supply component 711, a temperature control component 712, a spectroscopic component 713, a gas chamber to be tested 714, a reference gas chamber 715, a first photoelectric detection component 716, a second photoelectric detection component 717 and a signal processing component 718.

[0098] The power supply assembly 711 is connected to the quantum cascade laser 710 for applying a driving current to the quantum cascade laser 710. The temperature control assembly 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 assembly 71 may include a TEC thermoelectric cooler.

[0099] The quantum cascade laser 710 is connected to the beam splitter assembly 713 for injecting laser light into the beam splitter assembly 713. The beam splitter assembly 713 is connected to the gas chamber to be measured 714 and the reference gas chamber 715 for splitting the laser light and then transmitting the laser light to the gas chamber to be measured 714 and the reference gas chamber 715. The gas chamber to be measured contains multiple gases of a concentration to be measured, and the reference gas chamber contains a reference gas.

[0100] The first photoelectric detection assembly 716 and the second photoelectric detection assembly 717 are respectively connected to the gas chamber to be measured 714 and the reference gas chamber 715, and are used to respectively receive laser light passing through the gas chamber to be measured 714 and the reference gas chamber 715 and convert the laser light into a first electrical signal and a second electrical signal.

[0101] The signal processing component 718 is connected to the first photodetection component 716 and the second photodetection component 717 and is configured to calculate the concentrations of the plurality of gases based on the first electrical signal and the second electrical signal.

[0102] Preferably, the ratio of the lasers in the test gas chamber 714 and the reference gas chamber 715 is 1:1. This ratio may be a ratio of laser energy or intensity.

[0103] Figure 10 and Figure 11 FIG. 8 is a schematic structural diagram of a semiconductor laser 800 and its active region according to an embodiment of the present application, and is applicable to the detection method of any of the aforementioned embodiments. Figure 10 and Figure 11 As shown, the semiconductor laser 800 is a quantum cascade laser based on a Fabry-Perot cavity 810 , and includes an active region 820 that implements a diagonal transition.

[0104] like Figure 11 As shown, the active region 820 of the semiconductor laser 800 includes a transition region 821 and an injection region 822. In order to achieve a single longitudinal mode effect similar to a distributed feedback quantum cascade laser and to enable rapid wavelength modulation, a diagonal transition design is made for the active region of the quantum cascade laser of the Fabry-Perot resonant cavity. That is, the transition region 821 has more than two quantum wells, the upper energy level (ul) and the lower energy level (ll) are respectively in adjacent quantum wells, and the electron transition between adjacent quantum wells is in a diagonal direction. This structure enables the semiconductor laser 800 to achieve wide gain, which can reach a gain half-maximum width greater than 70cm. -1 Therefore, the quantum cascade laser based on the Fabry-Perot cavity has a simpler structure and lower production cost, and can achieve a wider wavelength scanning range.

[0105] The embodiments of the present application provide a method, device, and semiconductor laser for detecting the concentration of multiple gases. These methods utilize a grating-free quantum cascade laser with a Fabry-Perot resonant cavity. The quantum cascade laser is pre-characterized, and 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's center wavelength. The quantum cascade laser is then controlled to pass through the multiple gases within a preset time within the wavelength scanning window, obtaining signals indicating changes in the absorption intensity of the multiple gases. The concentrations of the multiple gases are then calculated based on these signals. Thus, the embodiments of the present application can achieve rapid and accurate simultaneous detection of the concentrations of multiple gases. Furthermore, due to the laser's simple structure, low production cost, and wide applicable detection range, the method has significant application value.

[0106] It should be noted that those skilled in the art will understand that the different implementation methods described in the method embodiments of the present application and their explanations and technical effects achieved are also applicable to the device embodiments of the present application and will not be repeated here.

[0107] While the exemplary embodiments of the present application have been described above, it should be understood that the exemplary embodiments are illustrative rather than restrictive, and the scope of protection of the present application is not limited thereto. It should be understood that those skilled in the art may modify and alter the embodiments of the present application without departing from the spirit and scope of the present application, and such modifications and alterations are intended to be within the scope of protection of the present application.

Claims

1. A method for detecting multi-gas concentrations, applicable to a quantum cascade laser with a Fabry-Perot cavity, characterized in that: The method comprises: The quantum cascade laser is pre-characterized, and a wavelength scanning window suitable for simultaneously detecting the concentrations of multiple gases is obtained by adjusting the heat sink temperature and driving current of the quantum cascade laser. The method 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, and arranging and combining the N temperature intervals and the 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 meet the wavelength scanning window from the experimental data of the N*M matrix; and obtaining a first functional relationship of the laser center wavelength varying with time within the wavelength scanning window, wherein the first functional relationship is: , where λ is the laser center wavelength, t is the preset time of the wavelength scanning window, tb and te represent the start time and end time of the preset time of the wavelength scanning window respectively; in the wavelength scanning window, within the preset time, the laser line width of the quantum cascade laser is less than the first threshold value, the moving range of the laser center wavelength of the quantum cascade laser is greater than the second threshold value so that the absorption peaks of the multiple gases are within the scanning range of the laser center wavelength, the laser center wavelength moves unidirectionally toward a longer wavelength or a shorter wavelength as time increases, and the first functional relationship Repeatable over a predetermined number of measurements with a central wavelength variation less than a predetermined percentage threshold; Control the quantum cascade laser to split the laser light emitted by the quantum cascade laser within the preset time of the wavelength scanning window, and then pass the laser light through the reference gas chamber and the gas chamber to be tested respectively, and obtain the first current value of the laser light intensity in the gas chamber to be tested varying with time. The second current value of the laser intensity in the reference gas chamber changes with time ; Calculate the first current value of the laser intensity in the gas chamber to be measured that changes with time The second current value of the laser intensity in the reference gas chamber changes with time The ratio between them is used to obtain the change signal of the absorption intensity of the laser by the multiple gases in the gas chamber to be measured. ,in, , and based on the change signal of the absorption intensity of the laser by the multiple gases The concentrations of the plurality of gases are calculated.

2. The method for detecting multiple gas concentrations according to claim 1, wherein: Calculating the concentrations of the multiple gases based on the change signals of the absorption intensities of the multiple gases to the laser light includes: based on And the first functional relationship The inverse function of , calculate and obtain the second functional relationship between the absorption intensity of the multiple gases for the laser and the central wavelength, , ; According to the second functional relationship between the absorption intensity of the multiple gases for the laser and 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.

3. The method for detecting multiple gas concentrations according to claim 2, wherein: The second functional relationship according to which the absorption intensity of the multiple gases for the laser changes with the central wavelength , obtaining the intensity of the absorption peak of each gas in the plurality of 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 central wavelength , obtaining the intensities of a plurality of absorption peaks of each of the plurality of gases; A plurality of concentration values ​​corresponding to each gas are calculated according to the intensities of the plurality of absorption peaks of each gas, and an average value of the plurality of concentration values ​​is calculated as the final concentration value of each gas.

4. The method for detecting multiple gas concentrations according to claim 2, wherein: The second functional relationship according to which the absorption intensity of the multiple gases for the laser changes with the central wavelength , obtaining the intensity of the absorption peak of each gas in the plurality of 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 central wavelength , obtaining the intensities of the multiple superimposed absorption peaks of the multiple gases; A multivariate equation group is constructed 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 the concentration value corresponding to each gas is calculated by solving the multivariate equation group.

5. The method for detecting multiple gas concentrations according to claim 1, wherein: The first threshold is 1 cm -1 , the second threshold is 10 cm -1 .

6. The method for detecting multiple gas concentrations according to claim 1, 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.

7. A multi-gas concentration detection device, suitable for the detection method according to any one of claims 1 to 6, characterized in that: include: A quantum cascade laser with a Fabry-Perot resonant cavity, a power supply component, a temperature control component, a spectroscopic 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 light splitting component, and laser light is incident on the light splitting component; The spectroscopic component is connected to the gas chamber to be measured and the reference gas chamber, and is used to split the laser and 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 respectively receive the laser passing through the gas chamber to be measured and the reference gas chamber and convert the output 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.

8. A semiconductor laser, suitable for use in the detection method according to any one of claims 1 to 6, characterized in that: The semiconductor laser is a quantum cascade laser with a Fabry-Perot resonant cavity, and includes an active region that realizes diagonal transition.

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