Terahertz full-band gas long-range transmissivity measuring method

Abstract

The invention relates to a terahertz full-band gas long-range transmissivity measuring method, which comprises the following steps of: constructing a folded light path in a sealed gas cavity, filling gas to be measured into the gas cavity, providing collimated terahertz waves of a frequency band to be measured for the folded light path through an incident optical window and an emergent optical window in the gas cavity, and measuring the long-range transmissivity of the terahertz full-band gas through the emergent optical window. The terahertz waves are reflected by the folded light path for multiple times to increase the transmission path in the to-be-measured gas, and then are emitted to the energy collection device from the emergent optical window, so that the energy of the terahertz waves in the to-be-measured frequency band after gas transmission is obtained, and then the energy of the terahertz waves in the to-be-measured frequency band after the same optical path is transmitted in vacuum is measured, so that the energy of the terahertz waves in the to-be-measured frequency band after gas transmission is obtained. And the transmissivity of the terahertz wave in the to-be-detected frequency band in the to-be-detected gas is obtained by dividing the two. And the long-range transmissivity measurement of the terahertz full-band in the corresponding gas is completed by replacing the terahertz waves with different frequency bands and different component gases. According to the method, the transmission path in the test gas is prolonged by folding the light path, meanwhile, the size of the light path is greatly compressed, and the measurement precision is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of long-range transmittance measurement of terahertz full-band gas, and in particular to a method for measuring long-range transmittance of terahertz full-band gas. Background Art

[0002] Compared with microwaves, terahertz electromagnetic waves have higher frequencies that can achieve higher resolution and wider bandwidth; compared with optical and infrared, longer wavelengths have stronger penetration. Therefore, terahertz has been widely studied in many fields such as radar, remote sensing and communications.

[0003] When electromagnetic waves in the terahertz band propagate in the gas, they will attenuate in the form of absorption. This attenuation is caused by the various molecules in the gas being excited to higher energy levels by the terahertz waves. Although many optical paths for measuring the transmission characteristics of gases in the terahertz band have been proposed, most of them are mainly direct transmission measurements. Moreover, for the long-range transmittance measurement of gases in the terahertz band, on the one hand, the optical path volume is relatively large, and on the other hand, it is susceptible to the instability of the terahertz signal source and the influence of the environment on the measurement results, resulting in the problem of inability to accurately obtain the transmittance. Summary of the invention

[0004] The purpose of the present invention is to provide a method for measuring the long-range transmittance of gas in the full terahertz frequency band, so as to solve at least one problem in the background technology.

[0005] In order to achieve the above object, the present invention provides a

[0006] A method for measuring the long-range transmittance of gas in the full terahertz frequency band, characterized by:

[0007] A folded optical path for extending the optical path is constructed in a sealed air cavity, wherein the air cavity has an incident optical window and an exit optical window, wherein the incident optical window and the exit optical window are respectively located on two opposite sides, and the air cavity is filled with a gas to be measured;

[0008] Adjusting the parameters of the folded optical path according to the gas to be measured, and adjusting the propagation path of the terahertz wave in the air cavity;

[0009] The collimated terahertz wave of the frequency band to be measured is provided to the folded optical path through the incident optical window. After the terahertz wave is reflected multiple times by the folded optical path in the gas to be measured and the transmission distance is increased, the terahertz wave is emitted from the exit optical window to the energy collection device to obtain the energy of the terahertz wave of the frequency band to be measured after transmission in the gas;

[0010] The air cavity is evacuated, and a collimated terahertz wave of the frequency band to be measured is provided to the folded optical path through the incident optical window. After the terahertz wave is reflected multiple times by the folded optical path in a vacuum environment to increase the transmission distance, it is emitted from the exit optical window to the energy collection device to obtain the energy of the terahertz wave of the frequency band to be measured after transmission in the vacuum;

[0011] The energy of the terahertz wave in the frequency band to be measured obtained after transmission in the gas is divided by the energy of the terahertz wave in the frequency band to be measured obtained after transmission in the vacuum, so as to obtain the transmittance of the terahertz wave in the frequency band to be measured in the gas to be measured.

[0012] Optionally, the transmittance of the low-frequency band and the high-frequency band of the terahertz wave are measured separately, and then the transmittance measurement of the full-band terahertz wave is obtained by splicing the frequency bands.

[0013] Optionally, when measuring the transmittance of low-frequency terahertz waves, the air cavity is placed between a transmitting antenna and a receiving antenna of a terahertz time-domain spectroscopy system, the transmitting antenna is used to transmit low-frequency terahertz waves, and the receiving antenna is used as an energy harvesting device to receive the energy of low-frequency terahertz magnetic waves after gas transmission;

[0014] When measuring the transmittance of high-frequency terahertz waves, a Fourier transform spectroscopy system is used to emit high-frequency terahertz waves, and a terahertz detector is used as an energy collection device to receive the energy of the high-frequency terahertz waves after gas transmission;

[0015] Optionally, when measuring the transmittance of low-frequency terahertz waves, the folded optical path is placed in the emission path of the terahertz time-domain spectroscopy system, satisfying the following relationship:

[0016]

[0017] Among them, L 产生 is the optical path of the terahertz wave from the beam splitter through the transmitting antenna and the folded optical path to the receiving antenna, L 探测 is the detection path optical length of the terahertz wave from the beam splitter to the receiving antenna, c is the speed of light, and n is an integer greater than or equal to 1.

[0018] Optionally, when measuring the transmittance of high-frequency terahertz waves, the folded optical path is placed in an optical path where two interference light beams of the Fourier transform spectroscopy system overlap.

[0019] Optionally, when measuring the transmittance of high-frequency terahertz waves, a first concave lens is arranged between the folded optical path and the Fourier transform spectroscopy system, and a second concave lens and a parabolic mirror are arranged in sequence between the folded optical path and the energy harvesting device.

[0020] Optionally, the folded optical path includes an incident reflector, an exit reflector and a plane reflector group, the plane reflector group includes a first plane reflector and a second plane reflector arranged in parallel and spaced apart, and the reflecting surfaces of the first plane reflector and the second plane reflector are arranged opposite to each other, the incident reflector and the exit reflector are respectively located on the outer sides of both ends of the plane reflector group and are arranged at an angle, the terahertz wave enters the plane reflector group through the incident reflector, and after multiple reflections between the two plane reflectors, is emitted from the energy collection device by the exit reflector.

[0021] Optionally, the air cavity is provided with an air inlet controlled by a valve and an air outlet controlled by a valve.

[0022] Optionally, the incident optical window and the exit optical window are made of polyethylene or diamond material.

[0023] Optionally, the frequency band of the low-frequency terahertz wave is 0.1-2 THz, and the frequency band of the high-frequency terahertz wave is 2-10 THz.

[0024] The above technical solution of the present invention has the following advantages:

[0025] The method for measuring the long-range transmittance of gas in the full terahertz frequency band provided by the present invention is to construct a folded optical path in a sealed gas cavity, fill the gas to be measured in the gas cavity, the gas cavity has an incident optical window and an exit optical window, provide a collimated terahertz wave of the frequency band to be measured to the folded optical path through the incident optical window, the terahertz wave is reflected multiple times by the folded optical path to increase the transmission distance in the gas to be measured, and then emits from the exit optical window to an energy collection device to obtain the energy of the terahertz wave of the frequency band to be measured after gas transmission, and then measure the energy of the terahertz wave of the frequency band to be measured after the same optical path is transmitted in vacuum, and divide the two to obtain the transmittance of the terahertz wave of the frequency band to be measured in the gas to be measured. By providing terahertz waves of different frequency bands and filling gases of different components, the long-range transmittance measurement of the full terahertz frequency band in the corresponding gas can be completed. This method extends the transmission distance in the test gas by folding the optical path, and at the same time greatly compresses the volume of the optical path, avoiding the disadvantage of not being able to accurately obtain gas attenuation during short optical path testing due to the unclear attenuation of the gas medium and the attenuation energy being lower than the normal fluctuation of the system signal, thereby ensuring measurement accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drawings of the present invention are provided for illustrative purposes only, and the proportions and quantities of the components in the drawings may not necessarily be consistent with the actual products.

[0027] Figure 1 It is a schematic diagram of a folded optical path and structure in an embodiment of the present invention;

[0028] Figure 2Schematic diagram of a transmittance measurement device for low-frequency terahertz waves in an embodiment of the present invention;

[0029] Figure 3 Schematic diagram of a high-frequency terahertz wave transmittance measurement device in an embodiment of the present invention;

[0030] Figure 4 It is a schematic diagram of the principle of terahertz wave detection when measuring the transmittance of low-frequency terahertz waves in an embodiment of the present invention.

[0031] In the figure:

[0032] 1: air cavity;

[0033] 11: incident optical window;

[0034] 12: exit optical window;

[0035] 13: Air inlet;

[0036] 14: air outlet;

[0037] 2: Folded optical path;

[0038] 21: incident reflector;

[0039] 22: exit reflector;

[0040] 23: plane reflector group;

[0041] 231: a first plane reflecting mirror;

[0042] 232: second plane reflecting mirror;

[0043] 24: Terahertz detector;

[0044] 25: first concave lens;

[0045] 26: second concave lens;

[0046] 27: Parabolic mirror. DETAILED DESCRIPTION

[0047] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0048] The method for measuring the long-range transmittance of gas in the full terahertz frequency band provided in the embodiment of the present invention mainly constructs a folded optical path in a sealed gas cavity, fills the gas to be measured in the gas cavity, and provides a collimated terahertz wave of the frequency band to be measured to the folded optical path through the incident optical window. After the terahertz wave is reflected multiple times by the folded optical path and increases the transmission distance in the gas to be measured, it is emitted from the exit optical window to the energy collection device to obtain the energy of the terahertz wave of the frequency band to be measured after transmission in the gas, and then the energy of the terahertz wave of the frequency band to be measured after the same optical path is transmitted in vacuum is measured, and the two are divided to obtain the transmittance of the terahertz wave of the frequency band to be measured in the gas to be measured. The long-range transmittance measurement of the full terahertz frequency band in the corresponding gas can be completed by providing terahertz waves of different frequency bands and filling gases of different components. This method extends the transmission distance in the test gas by folding the optical path, and at the same time greatly compresses the volume of the optical path, avoiding the disadvantage of not being able to accurately obtain gas attenuation during short optical path testing due to the unclear attenuation of the gas medium and the attenuation energy being lower than the normal fluctuation of the system signal, thereby ensuring measurement accuracy.

[0049] The present invention is further described below through specific embodiments:

[0050] like Figure 1 As shown, the sealed air cavity 1 is provided with an incident optical window 11 and an exit optical window 12 on opposite sides. A folded optical path 2 is constructed in the air cavity 1 to extend the optical path, and the air cavity 1 is filled with a gas to be measured, such as nitrogen or dry air.

[0051] The folded optical path 2 includes an incident reflector 21, an exit reflector 22 and a plane reflector group 23. The plane reflector group 23 includes a first plane reflector 231 and a second plane reflector 232 which are arranged in parallel and spaced apart. The reflection surfaces of the first plane reflector 231 and the second plane reflector 232 are arranged opposite to each other. The incident reflector 21 and the exit reflector 22 are respectively located outside the two ends of the plane reflector group 23 and are arranged at an angle. The angles of the incident reflector 21 and the exit reflector 22 are adjusted according to the gas to be measured, and the length of the plane reflector group 23 is selected to adjust the propagation path of the terahertz wave in the air cavity 1 so that it meets the optical path requirements. At the same time, the postures of the incident reflector 21, the exit reflector 22 and the energy harvesting device are adjusted to maximize the received energy. The incident reflector 21 introduces the incident terahertz wave into the plane reflector group 23. After multiple reflections in the plane reflector group 23, the terahertz wave is emitted by the exit reflector 22 to the energy harvesting device, and the energy P of the terahertz wave in the frequency band to be measured after gas transmission is obtained. 待测 The air cavity 1 is evacuated, and the collimated terahertz wave of the frequency band to be measured is provided to the folded optical path 2 through the incident optical window 11. After the terahertz wave is reflected multiple times by the folded optical path 2 in the vacuum environment to increase the transmission distance, it is emitted from the exit optical window 12 to the energy collection device to obtain the energy P of the terahertz wave of the frequency band to be measured after vacuum transmission.真空 Dividing the two gives the long-range transmittance of the terahertz wave in the gas to be measured:

[0052]

[0053] In order to make the terahertz wave signal source more stable, preferably, terahertz waves of different frequency bands are provided by different systems, and the transmittance of the low-frequency band and high-frequency band of the terahertz wave are measured separately, and then the transmittance measurement of the full-band terahertz is obtained by splicing the frequency bands.

[0054] See also Figure 2 As shown, in one example, when measuring the transmittance of low-frequency (0.1-2THz) terahertz waves, the air cavity 1 is placed between the transmitting antenna and the receiving antenna of the terahertz time-domain spectroscopy system. The transmitting antenna is used to transmit low-frequency terahertz waves, and the receiving antenna is used as an energy harvesting device to receive the energy of the low-frequency terahertz magnetic waves after transmission in the gas.

[0055] See also Figure 2 As shown, in one example, a lens is provided between the incident reflector 21 and the transmitting antenna, for collimating the divergent terahertz waves emitted by the transmitting antenna into parallel light. The lens may be a polyethylene lens, a TPX lens, or other lenses in the terahertz frequency band. A lens is provided between the exit reflector 22 and the receiving antenna, for focusing the emitted parallel terahertz waves onto the receiving antenna. The lens may be a polyethylene lens, a TPX lens, or other lenses in the terahertz frequency band.

[0056] Based on the detection principle of terahertz waves, terahertz detection is achieved by the terahertz pulse and the detection pulse meeting at the receiving end. In this embodiment, in order to improve the measurement accuracy and realize the long-range transmittance measurement of gas, the optical path is extended by folding the optical path, which results in the generation of an optical path L 产生 Increase and be greater than the detection light path L 探测 , which may make the measurement more random and uncontrollable, affecting the measurement efficiency. Based on this, in one embodiment, when measuring the transmittance of low-frequency terahertz waves, the folded optical path is placed in the emission path of the terahertz time-domain spectroscopy system and satisfies the following relationship:

[0057]

[0058] Among them, L 产生 is the optical path of the terahertz wave from the beam splitter through the transmitting antenna and the folded optical path to the receiving antenna, L 探测 is the detection path optical length of the terahertz wave from the beam splitter to the receiving antenna, c is the speed of light, and n is an integer greater than or equal to 1.

[0059] From the above relationship, it can be seen that when extending the optical path, preferably, the optical path L 产生and greater than the detection path optical path L 探测 n cycles. When n = 0, the generated optical path is equal to the detection optical path, and when n ≥ 1, the generated optical path is longer than the detection optical path.

[0060] The following takes n = 1 as an example to explain the detection principle in detail, that is, when the generated light path is longer than one cycle of the detection light path, Figure 4 As shown, the lasers are numbered 1, 2, 3, ..., N in the order of emission time, and the laser pulse repetition period is The laser is divided into two paths, the generation path and the detection path. The terahertz pulses excited by the generation path laser are represented in blue, and their repetition period is equal to the repetition period of the laser pulse. When the optical path of the generation path is greater than the optical path of the detection path, and the optical path of the generation path is adjusted to be greater than the optical path of the detection path by one pulse period, the terahertz pulse and the detection pulse can meet, realizing terahertz detection. Figure 4 Middle 1 探测 and 1 产生 The first laser pulse is split out. This detection mode is different from equal optical path detection. 探测 Pulse and 1 产生 The terahertz pulses excited by the pulse arrive at the detection antenna at the same time for detection, but 1 产生 Pulsed excitation of terahertz pulses and 2 探测 The laser pulses arrive at the detection antenna at the same time, using 2 探测 Laser pulse detection1 产生 Pulse-excited terahertz pulses, and so on.

[0061] See also Figure 3 As shown, when measuring the transmittance of high-frequency (2-10THz) terahertz waves, a Fourier transform spectroscopy system is used to emit high-frequency terahertz waves, and a terahertz detector 24 is used as an energy harvesting device to receive the energy of the high-frequency terahertz waves after gas transmission. In one example, the Vertex 80v vacuum Fourier transform spectrometer system is modified, and a movable reflector is used to lead the light path from the window to the gas cavity 1.

[0062] When measuring the transmittance of high-frequency terahertz waves, the folded optical path is placed in the optical path where two interference beams of the Fourier transform spectroscopy system overlap.

[0063] In one example, see Figure 3 As shown, when measuring the transmittance of high-frequency terahertz waves, a first concave lens 25 is arranged between the folded optical path and the Fourier transform spectroscopy system, and a second concave lens 26 and a parabolic mirror 27 are arranged in sequence between the folded optical path and the energy harvesting device. The first concave lens 25 cooperates with the parabolic mirror of the Fourier transform spectroscopy system to achieve beam shrinkage and collimation. The second concave lens 26 cooperates with the parabolic mirror 27 to achieve focusing.

[0064] It should be noted that the terahertz time-domain spectroscopy system and the Fourier transform spectroscopy system are both existing technologies and will not be described in detail here.

[0065] It should also be noted that the first concave lens 25 and the second concave lens 26 can be disposed in the air cavity 1 or outside the air cavity 1, which is not limited here.

[0066] To facilitate the operation of filling, deflating and changing gas, refer to Figure 1 As shown, in one example, the air cavity 1 is provided with an air inlet 13 with valve control and an air outlet 14 with valve control.

[0067] Preferably, the incident optical window 11 and the exit optical window 12 are high-transmittance windows. In one example, the incident optical window 11 and the exit optical window 12 are made of polyethylene or diamond material.

[0068] In summary, in this embodiment, the terahertz time domain spectroscopy system (THz-TDS) and Fourier transform spectroscopy technology (FTS) are used in conjunction with the folded optical path to respectively complete the measurement of terahertz low-frequency and high-frequency transmittance, and then the measurement data of the complete terahertz frequency band (0.1-10THz) is obtained by frequency band splicing. The folded optical path extends the transmission distance in the test gas and greatly compresses the volume of the optical path, thereby avoiding the problem that the gas attenuation cannot be accurately obtained during short optical path testing due to the unclear attenuation of the gas medium and the attenuation energy being lower than the normal fluctuation of the system signal, thereby ensuring the measurement accuracy.

[0069] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that not every embodiment contains only one independent technical solution. In the absence of a conflict of solutions, the various technical features mentioned in each embodiment can be combined in any manner to form other implementation methods that can be understood by those skilled in the art.

[0070] In addition, without departing from the scope of the present invention, the technical solutions described in the aforementioned embodiments may be modified, or some of the technical features may be replaced by equivalents, without causing the essence of the corresponding technical solutions to depart from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for measuring the long-range transmittance of gas in the full terahertz frequency band, characterized in that: A folded optical path for extending the optical path is constructed in a sealed air cavity, wherein the air cavity has an incident optical window and an exit optical window, wherein the incident optical window and the exit optical window are respectively located on two opposite sides, and the air cavity is filled with a gas to be measured; Adjusting the parameters of the folded optical path according to the gas to be measured, and adjusting the propagation path of the terahertz wave in the air cavity; The collimated terahertz wave of the frequency band to be measured is provided to the folded optical path through the incident optical window. After the terahertz wave is reflected multiple times by the folded optical path in the gas to be measured to increase the transmission distance, it is emitted from the exit optical window to the energy collection device to obtain the energy of the terahertz wave of the frequency band to be measured after transmission in the gas; The air cavity is evacuated, and a collimated terahertz wave of the frequency band to be measured is provided to the folded optical path through the incident optical window. After the terahertz wave is reflected multiple times by the folded optical path in a vacuum environment to increase the transmission distance, it is emitted from the exit optical window to the energy collection device to obtain the energy of the terahertz wave of the frequency band to be measured after transmission in the vacuum; The energy of the terahertz wave in the frequency band to be measured obtained after transmission in the gas is divided by the energy of the terahertz wave in the frequency band to be measured obtained after transmission in the vacuum, so as to obtain the transmittance of the terahertz wave in the frequency band to be measured in the gas to be measured.

2. The measuring method according to claim 1, characterized in that: The transmittance of the low-frequency band and high-frequency band of the terahertz wave is measured separately, and then the transmittance measurement of the full-band terahertz wave is obtained by splicing the frequency bands.

3. The measuring method according to claim 2, characterized in that: When measuring the transmittance of low-frequency terahertz waves, the air cavity is placed between the transmitting antenna and the receiving antenna of the terahertz time-domain spectroscopy system, the transmitting antenna is used to transmit low-frequency terahertz waves, and the receiving antenna is used as an energy harvesting device to receive the energy of the low-frequency terahertz magnetic waves after gas transmission; When measuring the transmittance of high-frequency terahertz waves, a Fourier transform spectroscopy system is used to emit high-frequency terahertz waves, and a terahertz detector is used as an energy harvesting device to receive the energy of the high-frequency terahertz waves after gas transmission.

4. The measuring method according to claim 3, characterized in that: When measuring the transmittance of low-frequency terahertz waves, the folded optical path is placed in the emission path of the terahertz time-domain spectroscopy system, satisfying the following relationship: Among them, L 产生 is the optical path of the terahertz wave from the beam splitter through the transmitting antenna and the folded optical path to the receiving antenna, L 探测 is the detection path optical length of the terahertz wave from the beam splitter to the receiving antenna, c is the speed of light, and n is an integer greater than or equal to 1.

5. The measuring method according to claim 3 or 4, characterized in that: When measuring the transmittance of high-frequency terahertz waves, the folded optical path is placed in the optical path where two beams of interference light of the Fourier transform spectroscopy system overlap.

6. The measuring method according to claim 5, characterized in that: When measuring the transmittance of high-frequency terahertz waves, a first concave lens is arranged between the folded optical path and the Fourier transform spectroscopy system, and a second concave lens and a parabolic mirror are arranged in sequence between the folded optical path and the energy harvesting device.

7. The measuring method according to claim 1, characterized in that: The folded optical path includes an incident reflector, an exit reflector and a plane reflector group. The plane reflector group includes a first plane reflector and a second plane reflector that are arranged in parallel and spaced apart, and the reflection surfaces of the first plane reflector and the second plane reflector are arranged opposite to each other. The incident reflector and the exit reflector are respectively located on the outer sides of the two ends of the plane reflector group and are arranged at an angle. The terahertz wave enters the plane reflector group through the incident reflector, and after multiple reflections between the two plane reflectors, it is emitted from the energy collection device by the exit reflector.

8. The measuring method according to claim 1, characterized in that: The air cavity is provided with an air inlet controlled by a valve and an air outlet controlled by a valve.

9. The measuring method according to claim 1, characterized in that: The incident optical window and the exit optical window are made of polyethylene or diamond material.

10. The measuring method according to claim 2, characterized in that: The frequency band of low-frequency terahertz waves is 0.1-2THz, and the frequency band of high-frequency terahertz waves is 2-10THz.

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