Terahertz wave-based high-integration and multi-reflection gas content detection device and detection method and application thereof

Abstract

The invention discloses a high-integration and multi-reflection gas content detection device based on terahertz waves, and relates to the technical field of gas detection, and the high-integration and multi-reflection gas content detection device comprises a terahertz quantum cascade laser, an information acquisition device, a first parabolic mirror, a gas chamber, a second parabolic mirror, a spherical reflection cavity and a reflector. According to the invention, the structure of the laser detector is optimized, the terahertz quantum cascade laser self-mixing technology is utilized to realize accurate detection, the multi-reflection technology is adopted to increase the optical path so as to improve the measurement accuracy, and a high-sensitivity, rapid, continuous and safe detection means is provided.

Description

Technical Field

[0001] The present invention relates to the technical field of gas detection, and in particular to a highly integrated, multi-reflection gas content detection device based on terahertz waves, and a detection method and application thereof. Background Art

[0002] Ethylene is a plant hormone that plays a key role in regulating the ripening and aging process of fruits and vegetables. In the later stages of their growth, fruits and vegetables will produce ethylene, which will trigger a series of physiological reactions, such as respiratory rupture, which will speed up the respiration rate of fruits and vegetables and accelerate the ripening and decay process. For example, bananas produce a large amount of ethylene during the ripening process. Once the concentration of ethylene reaches a certain threshold, the bananas will quickly turn yellow and soften.

[0003] However, due to the limitations of traditional detection methods, for example, traditional chemical detection methods such as gas chromatography are more accurate, but the operation is complicated and time-consuming, and requires professionals to collect and analyze samples, and cannot achieve real-time and continuous monitoring. At the same time, these methods usually require samples to be brought back to the laboratory and undergo complex pre-treatment steps, including extraction, concentration, etc., and then analyzed, and cannot timely feedback the dynamic changes of ethylene concentration in the fruit shed; and electrochemical sensor detection methods: There are problems such as poor selectivity, susceptibility to interference, and limited service life. In the fruit shed environment, due to humidity, temperature changes, and the presence of other gas components (such as carbon dioxide, ammonia, etc.), electrochemical sensors may make misjudgments, and their detection accuracy may decrease after long-term use.

[0004] Therefore, how to provide a detection method that can efficiently and continuously detect the ethylene content in the greenhouse in real time with high sensitivity and selectivity is a technical problem that urgently needs to be solved in this field. Summary of the invention

[0005] In view of this, the purpose of the present invention is to provide a highly integrated, multi-reflection gas content detection device based on terahertz waves, in which the QCL active region is designed within the 3.8-4.0THz gain bandwidth and is grown on a GaAs substrate using molecular beam epitaxy technology; the gas optical spectrum system structure includes a parabolic mirror for collimating terahertz radiation, a glass gas chamber and a spherical reflection cavity container to achieve multiple reflections and amplification of the light beam; the detection method involves monitoring the voltage change of the QCL terminal, recording the terahertz feedback phase shift, and analyzing the signal using fast Fourier transform and regression Gaussian function, and comparing it with the terahertz database of ethylene to determine the ethylene content, meeting the requirements of high sensitivity, short detection time, long duration, safety, etc.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] A highly integrated, multi-reflection gas content detection device based on terahertz waves, comprising a terahertz quantum cascade laser, an information collection device, a first parabolic mirror, a gas chamber, a second parabolic mirror, a spherical reflection cavity and a reflector;

[0008] Wherein, the terahertz quantum cascade laser is used to generate a first laser beam;

[0009] The first parabolic mirror is used to change the path of the first laser beam so that the first laser beam is emitted to the gas chamber;

[0010] The gas chamber is used to irradiate the first laser beam on the gas to be detected to generate a second laser beam carrying the sample to be detected, and emit it to the second parabolic mirror;

[0011] The second parabolic mirror is used to change the path of the second laser beam so that the second laser beam is emitted into the spherical reflection cavity;

[0012] The spherical reflection cavity increases the optical path by reflecting and amplifying the second laser beam three-dimensionally and multiple times in the cavity, and emits it to the reflection mirror;

[0013] The reflector is used to reflect the second laser beam so that it is reflected back to the terahertz quantum cascade laser along the same optical path;

[0014] The information acquisition device is used to collect and analyze the signal and determine the components of its main frequency, thereby obtaining the terahertz spectrum of the ambient gas and judging the real-time content of the gas.

[0015] Laser detectors can accurately select the laser wavelength corresponding to the gas absorption spectrum and detect only the target gas without interference from other gases. For example, by accurately adjusting the laser wavelength to the specific absorption line of the ethylene molecule (such as in the near-infrared band), highly selective detection can be achieved, and the ethylene concentration can be detected in situ and in real time in the fruit shed environment without the need for complicated sample collection and pretreatment processes. It can be installed in a suitable position in the fruit shed to continuously monitor the ethylene concentration and provide fruit farmers with timely information on changes in ethylene concentration so that they can take corresponding measures, such as ventilation and temperature adjustment, to control the ripening speed of fruits and vegetables. Laser detection is a non-contact detection method that will not cause any physical damage to fruits and vegetables, nor will it affect the normal growth environment of fruits and vegetables, which is very important for ensuring the quality of fruits and vegetables.

[0016] And regarding terahertz waves, their spatial resolution is better than that of microwaves, and even has better penetration than infrared rays. Terahertz waves have the characteristic of low photon energy and will not destroy the organic structure of various substances in the greenhouse. Each substance itself contains a lot of information, which can be presented through the terahertz spectrum. Due to the vibration and rotation energy levels of chemical molecules such as hydrogen bonds, van der Waals forces and dipole rotations between or within molecules of different substances, they correspond to the terahertz frequency band. In particular, many organic molecules have energy levels in this band, which makes their molecules have unique fingerprint (absorption) spectra in the terahertz band. Related research on the THz absorption spectrum of ethylene has proved that these dangerous gases have obvious fingerprint (absorption) spectra in the THz band, which can fully lay a solid foundation for this invention.

[0017] The advantages of this device include: terahertz photons have low energy and are harmless to the human body; the highly integrated design reduces the volume, reduces energy loss, and improves measurement accuracy; it can detect ethylene concentration in situ and in real time in the fruit shed without the need for complex sample collection and preprocessing, providing fruit farmers with timely information on changes in ethylene concentration so that they can take appropriate measures to control the ripening speed of fruits and vegetables.

[0018] Preferably, a first Brewster angle window and a second Brewster angle window are respectively provided on both sides of the gas chamber, and the first laser beam passes through the first Brewster angle window to reach the inner cavity of the gas chamber to be measured, and then passes through the second Brewster angle window to be emitted to the second parabolic mirror.

[0019] Preferably, the gas chamber is made of transparent material and has an opening that is not sealed, thereby connecting the gas chamber to the external environment.

[0020] Preferably, the inner surface of the spherical reflection cavity is coated with an aluminum film with a high reflection coefficient.

[0021] Preferably, the reflector is a plane reflector with a circular cross-section.

[0022] Preferably, the terahertz quantum cascade laser has a gain bandwidth of 3.8-4.0 THz, and the structure is grown on a semi-insulating GaAs substrate using molecular beam epitaxy technology.

[0023] Preferably, the structure is as follows: after the initial 250-280nm thick GaAs buffer layer, there is a 300-340nm thick Al0.5Ga0.5As etch stop layer and a 700-800nm ​​thick n-GaAs contact layer, 115-118 cycles of AR (anti-reflection) layer are grown to a thickness of 14.4-14.6μm, followed by a 50-54nm thick n-GaAs top contact layer, and finally a 150-153μm wide gold plasma ridge waveguide structure is determined using photolithography technology.

[0024] Preferably, the Si doping density of the n-GaAs contact layer is ρ=2×10 18 ~2.2×10 18 cm -3 The Si doping density of the n-GaAs top contact layer is ρ=5×10 18 ~5.2×10 18 cm -3 .

[0025] Preferably, the Si doping density of the n-GaAs contact layer is ρ=2×1018cm -3 The Si doping density of the n-GaAs top contact layer is ρ = 5 × 1018 cm -3 .

[0026] According to the above-mentioned detection method of a highly integrated, multi-reflection gas content detection device based on terahertz waves, the following steps are included:

[0027] The first laser beam emitted by the terahertz quantum cascade laser is guided to the first Brewster angle window through the first parabolic mirror, passes through the window to reach the gas chamber to be measured to obtain the second laser beam, and then passes through the second Brewster angle window to be emitted to the second parabolic mirror. The second laser beam is incident on the spherical reflection cavity at an ideal angle of 45° in a low-loss state, is amplified after multiple reflections, and is emitted at an ideal angle of 45°, and finally hits the reflector to reflect the second laser beam, so that it returns to the terahertz quantum cascade laser along the same optical path. Finally, the information collector is used to collect and analyze the signal and determine the component of its main frequency, thereby obtaining the terahertz spectrum of the ambient gas, and the terahertz absorption spectrum of the detected environment is compared with the terahertz database of the gas, thereby judging the real-time content of the gas.

[0028] As described above, a highly integrated, multi-reflection gas content detection device based on terahertz waves is applied in real-time gas detection.

[0029] Preferably, the gas is ethylene.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) The terahertz photon energy used in the present invention is low and will not produce an ionization effect, so the human body will not be harmed in a greenhouse environment for a long time;

[0032] (2) In the device of the present invention, the light beam is reflected multiple times in the spherical cavity and is continuously amplified. Stereo reflection is used to minimize the total volume of the system while achieving the expected effect. The high integration makes the spacing between components small, the energy loss is low, and the measurement accuracy is higher.

[0033] (3) The detection device of the present invention can detect the ethylene concentration in situ and in real time in the fruit shed environment without complicated sample collection and pretreatment processes. It can be installed at a suitable location in the fruit shed to continuously monitor the ethylene concentration. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. The drawings in this description are only embodiments of the present invention.

[0035] Figure 1 This is a structural diagram of a highly integrated, multi-reflection gas content detection device based on terahertz waves of the present invention. DETAILED DESCRIPTION

[0036] Embodiments of the present invention are described below. Examples of the embodiments are shown in the accompanying drawings. The embodiments described with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, but are not to be construed as limiting the present invention.

[0037] Example 1

[0038] like Figure 1 The present invention provides a highly integrated, multi-reflection gas content detection device based on terahertz waves, which is used for ethylene content detection in greenhouses, and specifically comprises a terahertz quantum cascade laser 1, an information collection device 2, a first parabolic mirror 3, a glass gas chamber 9, a second parabolic mirror 6, a spherical reflection cavity 7 and a reflection mirror 8;

[0039] The terahertz quantum cascade laser 1 is used to generate the first laser beam; the QCL active region is designed to set the size to a 3.8-4.0THz gain bandwidth, and the structure is grown on a semi-insulating GaAs substrate using molecular beam epitaxy technology, and the specific method is: after the initial 280nm thick GaAs buffer layer, there is a 340nm thick Al0.5Ga0.5As etching stop layer and an 800nm ​​thick n-GaAs contact layer, and the Si doping density in the n-GaAs contact layer is ρ=2×1018cm -3 , then 118 cycles of AR (anti-reflection) layer were grown to a thickness of 14.6 μm, followed by 54 nm thick n-GaAs (Si doping density ρ = 5 × 1018 cm -3 ) top contact layer; using photolithography to determine a 153 μm wide gold plasma ridge waveguide structure and cut it into 1.9 mm long;

[0040] The first parabolic mirror 3 is used to change the path of the first laser beam so that the first laser beam is emitted to the glass gas chamber 9;

[0041] The glass gas chamber 9 is used to irradiate the first laser beam on the gas to be detected to generate a second laser beam carrying the sample to be detected, and emit it to the second parabolic mirror 6; the first Brewster angle window 4 and the second Brewster angle window 5 are respectively arranged on both sides of the glass gas chamber 9, the first laser beam passes through the first Brewster angle window 4 to reach the inner cavity of the glass gas chamber 9 to be detected, and then passes through the second Brewster angle window 5 to be emitted to the second parabolic mirror 6; the glass gas chamber 9 is not closed and has an opening, which connects the gas chamber with the external environment, so that the system can measure the ethylene content in the environment in real time;

[0042] The second parabolic mirror 6 is used to change the path of the second laser beam so that the second laser beam is emitted into the spherical reflection cavity 7;

[0043] The spherical reflection cavity 7 increases the optical path by reflecting and amplifying the second laser beam three-dimensionally and multiple times in the cavity, and then emits it to the reflector 8; the inner surface of the spherical reflection cavity 7 is coated with a layer of aluminum film with a high reflection coefficient, so that the light beam is three-dimensionally and multiple times reflected and amplified in the cavity, increasing the optical path and making the measurement more accurate; and controlling an ideal incident angle can ensure that the laser beam can be emitted from the cavity at another angle;

[0044] The reflector 8 is a circular cross-section plane reflector, used to reflect the second laser beam back to the terahertz quantum cascade laser 1 along the same optical path;

[0045] The information acquisition device 2 is a multifunctional multi-channel information acquisition instrument, which is used to collect and analyze signals and determine the components of their main frequencies, thereby obtaining the terahertz spectrum of the ambient gas and determining the real-time content of the gas;

[0046] The terahertz radiation from the QCL of this device is collimated by a silver-plated 90° off-axis first parabolic mirror with a diameter of 20mm and an effective focal length of 70mm, and guided through a 100cm long glass gas chamber. Two first and second 3mm thick polymethylpentene cloth windows are set on both sides of the glass gas chamber to transmit the flat-band terahertz with a loss of less than 1%. The transmitted light beam is collimated through the window by a silver-plated 90° off-axis second parabolic mirror to guide the transmitted light beam into a designed spherical reflection cavity container. The inner wall of the spherical container is coated with a metal aluminum coating to ensure that the light loss is minimized and the laser output efficiency is improved. The incident angle entering the spherical container is 45°, so that the light beam is reflected multiple times in the spherical cavity and is continuously amplified and finally emitted. At the final end of this system, a circular cross-section plane reflector is used to reflect the terahertz beam along the same optical path and return to the QCL cavity, repeatedly reflecting the light back to the active area, thereby increasing the gain length of the light in the active area;

[0047] The detection method is to use an AC-coupled data acquisition board to monitor the voltage across the QCL terminals. It only needs to record the perturbation caused by sm over time. The QCL is biased with a constant DC current and the voltage is 110 mm. -1 The delay stage is translated along its entire length at a speed of , and the resulting terahertz feedback phase shift causes a periodic SM interference effect in the QCL. The corresponding voltage disturbance vSM(t) is recorded as a function of the round-trip delay time. Finally, the spectrum of the measured interference pattern can be obtained by fast Fourier transform, and the regression Gaussian function is used to analyze the signal and determine the component of its main frequency. The terahertz absorption spectrum of the detected environment is compared with the terahertz database of ethylene to determine the real-time ethylene content.

[0048] Application Examples

[0049] A large agricultural enterprise has multiple modern greenhouses for growing high-value fruits and vegetables. Due to the influence of ethylene on the maturation process of plants, accurate control of ethylene content is crucial to improving product quality and extending shelf life. The gas content detection device of the present invention is used to monitor the relevant ethylene gas content, specifically:

[0050] A highly integrated, multi-reflection gas content detection device based on terahertz waves of Example 1 is installed in each greenhouse. Each device includes a terahertz laser, which can emit terahertz waves of specific frequencies corresponding to the characteristic absorption frequencies of ethylene molecules. The gas in the greenhouse enters the laser and reaches the measurement area of ​​the terahertz laser. After the terahertz wave passes through the gas sample, the changes in its intensity and phase are captured by a terahertz time domain spectrometer (THz-TDS). By analyzing these changes, the concentration information of ethylene gas can be obtained.

[0051] The voltage across the QCL terminals can be well monitored by an AC-coupled data acquisition board. Simply record the time-varying perturbation caused by sm. The QCL is biased with a constant DC current and operated at 110 mm -1 The delay stage is translated over its entire length at a speed of , and the resulting terahertz feedback phase shift leads to a periodic SM interference effect in the QCL. The corresponding voltage perturbation v SM (t) is recorded as a function of the round-trip delay time. Finally, the frequency spectrum of the measured interference pattern can be obtained by fast Fourier transform, and the regression Gaussian function is used to analyze the signal and determine the components of its main frequency. The terahertz absorption spectrum of the detected environment is compared with the terahertz database of ethylene to determine the real-time ethylene content. Once the ethylene content is detected to exceed the preset threshold, the system will automatically adjust the ventilation system in the greenhouse or release ethylene absorbent to maintain the ethylene content within the optimal range.

[0052] The system can monitor ethylene levels in real time and send alarms to farm managers via mobile apps or text messages when levels are abnormal so that timely measures can be taken.

[0053] Effect:

[0054] By deploying a terahertz laser measurement system, the agricultural enterprise can accurately control the ethylene content in each greenhouse, thereby optimizing the plant growth environment, improving fruit quality, extending the shelf life, and increasing economic benefits; in addition, the system also reduces the cost and time of manual inspection, and improves the convenience and accuracy of operation. This example demonstrates the potential of terahertz technology in modern agricultural greenhouse gas monitoring, especially when it is necessary to accurately control the ethylene content in the plant growth environment. With the further development of terahertz technology, its application in the field of smart agriculture will become more and more extensive.

[0055] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A highly integrated, multi-reflection gas content detection device based on terahertz waves, characterized in that: It includes a terahertz quantum cascade laser, an information collection device, a first parabolic mirror, a gas chamber, a second parabolic mirror, a spherical reflection cavity and a reflection mirror; Wherein, the terahertz quantum cascade laser is used to generate a first laser beam; The first parabolic mirror is used to change the path of the first laser beam so that the first laser beam is emitted to the gas chamber; The gas chamber is used to irradiate the first laser beam on the gas to be detected to generate a second laser beam carrying the sample to be detected, and emit it to the second parabolic mirror; The second parabolic mirror is used to change the path of the second laser beam so that the second laser beam is emitted into the spherical reflection cavity; The spherical reflection cavity increases the optical path by reflecting and amplifying the second laser beam three-dimensionally and multiple times in the cavity, and emits it to the reflection mirror; The reflector is used to reflect the second laser beam so that it is reflected back to the terahertz quantum cascade laser along the same optical path; The information acquisition device is used to collect and analyze the signal and determine the components of its main frequency, thereby obtaining the terahertz spectrum of the ambient gas and judging the real-time content of the gas.

2. A highly integrated, multi-reflection gas content detection device based on terahertz waves according to claim 1, characterized in that: A first Brewster's angle window and a second Brewster's angle window are respectively provided on both sides of the gas chamber. The first laser beam passes through the first Brewster's angle window to reach the inner cavity of the gas chamber to be measured, and then passes through the second Brewster's angle window to be emitted to the second parabolic mirror.

3. The highly integrated, multi-reflection gas content detection device based on terahertz waves according to claim 1, characterized in that: The gas chamber is made of transparent material and has an opening which is not sealed, so that the gas chamber is connected with the external environment.

4. The highly integrated, multi-reflection gas content detection device based on terahertz waves according to claim 1, characterized in that: The inner surface of the spherical reflection cavity is plated with an aluminum film with a high reflection coefficient.

5. The highly integrated, multi-reflection gas content detection device based on terahertz waves according to claim 1, characterized in that: The reflector is a plane reflector with a circular cross section.

6. The highly integrated, multi-reflection gas content detection device based on terahertz waves according to claim 1, characterized in that: The terahertz quantum cascade laser has a gain bandwidth of 3.8-4.0 THz, and the structure is grown on a semi-insulating GaAs substrate using a molecular beam epitaxy technique.

7. A highly integrated, multi-reflection gas content detection device based on terahertz waves according to claim 6, characterized in that: The structure is specifically as follows: after the initial 250-280nm thick GaAs buffer layer, there is a 300-340nm thick Al0.5Ga0.5As etch stop layer, a 700-800nm ​​thick n-GaAs contact layer, a 14.4-14.6μm thick AR anti-reflection layer and a 50-54nm thick n-GaAs top contact layer, and then a 150-153μm wide gold plasma ridge waveguide structure is determined using photolithography technology.

8. The highly integrated, multi-reflection gas content detection device based on terahertz waves according to claim 7, characterized in that: The Si doping density of the n-GaAs contact layer is ρ=2×10 18 ~2.2×10 18 cm -3 The Si doping density of the n-GaAs top contact layer is ρ=5×10 18 ~5.2×10 18 cm -3 .

9. A detection method for a highly integrated, multi-reflection gas content detection device based on terahertz waves according to any one of claims 1 to 8, characterized in that: The following steps are involved: The first laser beam emitted by the terahertz quantum cascade laser is guided to the first Brewster angle window through the first parabolic mirror, passes through the window to reach the gas chamber to be measured to obtain the second laser beam, and then passes through the second Brewster angle window to be emitted to the second parabolic mirror. The second laser beam is incident on the spherical reflection cavity at an ideal angle of 45° in a low-loss state, is amplified after multiple reflections, and is emitted at an ideal angle of 45°, and finally hits the reflector to reflect the second laser beam, so that it returns to the terahertz quantum cascade laser along the same optical path. Finally, the information collector is used to collect and analyze the signal and determine the component of its main frequency, thereby obtaining the terahertz spectrum of the ambient gas, and the terahertz absorption spectrum of the detected environment is compared with the terahertz database of the gas, thereby judging the real-time content of the gas.

10. Application of a highly integrated, multi-reflection gas content detection device based on terahertz waves as claimed in any one of claims 1 to 8 in real-time detection of gas content.

Images