Method and apparatus for simultaneous measurement of gas refractive index and concentration based on quantum light source

Abstract

The application discloses a kind of method and device for simultaneously measuring gas refractive index and concentration based on quantum light source, the method is: step one, entangled light or compressed light emitted by quantum light source is collimated after passing through optical isolation and polarization state conversion, after being split, respectively incident to reference cavity and measurement cavity, wherein, reference cavity and measurement cavity are both composed of two SPDC crystals arranged side by side, and reference cavity and measurement cavity are placed inside vacuum chamber, and the vacuum chamber is filled with the gas to be measured;The distance between the two SPDC crystals of reference cavity and the nearest distance between the two SPDC crystals of measurement cavity are different;Step two, the laser emitted from reference cavity and measurement cavity respectively passes through optical filtering, focuses after filtering out pump light, and then respectively incident to beam splitter, the laser passing through beam splitter is divided into transmitted light and reflected light, two transmitted lights are detected and received by CCD camera, and the concentration value of the gas to be measured is obtained by analyzing its interference pattern;Two reflected lights are detected and received by frequency meter, and the refractive index value of the gas to be measured is obtained by analyzing the double-cavity beat frequency before and after the vacuum chamber is filled with the gas to be measured.The application can realize the simultaneous measurement of gas refractive index and gas concentration, and solve the problem of high sensitivity detection of gas refractive index and gas concentration.

Description

Technical Field

[0001] This invention belongs to the field of laser spectroscopy measurement technology, specifically relating to a method and apparatus for simultaneously measuring the refractive index and concentration of a gas based on a quantum light source. Background Technology

[0002] The measurement of gas refractive index and gas concentration has important applications in many fields. For example, in environmental monitoring, the detection of gas concentration can help us better understand atmospheric environmental conditions. In precision manufacturing, the measurement of gas refractive index can be used to compensate for the measurement accuracy of parameters such as displacement, thereby improving measurement accuracy.

[0003] However, traditional gas detection methods often only measure gas refractive index or gas concentration individually, with limited accuracy and sensitivity. Gas refractive index and concentration detection are affected by various factors, including temperature, pressure, gas composition, and concentration. Traditional gas detection techniques often struggle to maintain high accuracy in refractive index measurement under all conditions, especially in complex and variable environments. Furthermore, the environment can affect the density and distribution of gas molecules, thus influencing the strength and stability of the detection signal. High-precision gas refractive index or gas concentration measurement equipment is complex in structure and difficult to operate. Moreover, traditional methods are susceptible to environmental interference; impurities and moisture in the gas can interfere with the measurement, affecting the accuracy of the results. Summary of the Invention

[0004] In view of this, the present invention provides a method and apparatus for simultaneous measurement of gas refractive index and concentration based on quantum light source, which can realize the simultaneous measurement of gas refractive index and gas concentration, and solve the problem of high-sensitivity detection of gas refractive index and gas concentration.

[0005] This invention is achieved through the following technical solution:

[0006] A method for simultaneously measuring the refractive index and concentration of a gas based on a quantum light source, the specific steps of which are as follows:

[0007] Step 1: The entangled or compressed light emitted by the quantum light source is collimated, optically isolated, and polarization-state converted. After being split, it is incident on the reference cavity and the measurement cavity, respectively. Both the reference cavity and the measurement cavity are composed of two SPDC crystals arranged in parallel. Both the reference cavity and the measurement cavity are placed inside a vacuum chamber, which is filled with the gas to be measured during operation. The two SPDC crystals in the reference cavity and the two SPDC crystals in the measurement cavity have the same thickness, but the distance between the two SPDC crystals in the reference cavity and the closest distance between the two SPDC crystals in the measurement cavity are different.

[0008] Step two: The laser beams emitted from the reference cavity and the measurement cavity are filtered to remove the pump light and then focused before being incident on the beam splitter. The laser beams after passing through the beam splitter are split into transmitted light and reflected light. The two transmitted beams are detected and received by a CCD camera, and their interference patterns are analyzed to obtain the concentration value of the gas to be measured. The two reflected beams are detected and received by a frequency meter, and the refractive index value of the gas to be measured is obtained by analyzing the beat frequency of the dual cavities before and after the gas to be measured is filled into the vacuum chamber.

[0009] Furthermore, in step one, both the reference cavity and the measurement cavity are composed of two SPDC crystals. When a beam of entangled or compressed light emitted from the quantum light source is incident on the first SPDC crystal, the first SPDC crystal converts the beam of entangled or compressed light into downconverted photons, which include a beam of signal light and a beam of idler light. Then, the beam of signal light and the beam of idler light are injected into the second SPDC crystal, which converts them into two beams of signal light and two beams of idler light. The downconverted photons from the two SPDC crystals interfere and obtain an interference pattern.

[0010] In step two, the specific process of obtaining the concentration value of the gas to be measured based on the interference pattern is as follows:

[0011] The closest distance between two SPDC crystals of thickness L is L m The interference pattern is detected and received by a CCD camera; the interference pattern of the signal light is represented as follows:

[0012]

[0013] In the formula, I s λ is the intensity of the signal light. s Let θ be the wavelength of the signal light. s The divergence angle of the signal light. The transmittance of the medium to the amplitude of the idler frequency light and δ is the absorption coefficient of the gas to be measured; δ is the total phase obtained from the signal light, idler light, and pump light; δ m Because of the L before and after inflation m The phase change caused by the change;

[0014] The absorption coefficient of the gas to be measured can be obtained from formula (1). Based on the absorption coefficient of the gas to be measured The concentration of the gas to be measured can be obtained by relating it to the concentration of the gas being measured. The formula for calculating the concentration of the gas to be measured is as follows:

[0015]

[0016] In the formula, c is the concentration of the gas to be measured, T is the temperature of the gas to be measured, K′ is a constant, p is atmospheric pressure, and ξ is the water vapor content factor.

[0017] Furthermore, in step two, the specific process of obtaining the refractive index value of the gas to be tested based on the dual-cavity beat frequency before and after the gas to be tested is as follows:

[0018] First, measure the beat frequency of the dual cavities when they are in high vacuum and the initial frequency of the laser under high vacuum. Then, measure the beat frequency of the dual cavities when they are filled with the gas to be tested. The formula for calculating the refractive index n of the gas to be tested is as follows:

[0019]

[0020] In the formula, v r ν represents the initial frequency of the laser under high vacuum. beati For dual-chamber beat frequency before inflation; ν beatf The frequency of the dual-cavity pulse after inflation; Δm is the change in the longitudinal mode of the laser before and after inflation; ν FSR The free spectral range is given, Δp is the change in pressure of the gas to be measured, and K is the bulk modulus of the SPDC crystal material.

[0021] A device for simultaneous measurement of gas refractive index and concentration based on a quantum light source, the device comprising: a quantum light source, a collimating lens, an optical isolator, a waveplate, a beam splitter, a reference cavity, a first filter, a first focusing lens, a mirror, a measurement cavity, a second filter, a second focusing lens, a first beam splitter, a first laser collimator, a second beam splitter, a second laser collimator, a third laser collimator, a CCD camera, a first photodetector, a second photodetector, a frequency counter, a computer, and a vacuum chamber;

[0022] The vacuum chamber is filled with the gas to be tested;

[0023] Both the reference cavity and the measurement cavity are placed inside the vacuum chamber; the reference cavity consists of two SPDC crystals arranged side by side, SPDC crystal one and SPDC crystal two; the measurement cavity consists of two SPDC crystals arranged side by side, SPDC crystal three and SPDC crystal four; the thicknesses of SPDC crystal one, SPDC crystal two, SPDC crystal three and SPDC crystal four are equal; the closest distance between SPDC crystal one and SPDC crystal two is different from the closest distance between SPDC crystal three and SPDC crystal four;

[0024] The quantum light source generates entangled or compressed light. The entangled or compressed light is collimated by a collimating lens and then passes through an optical isolator. The emitted light undergoes polarization state conversion by a waveplate and is then incident on a beam splitter to split the light, forming transmitted light and reflected light.

[0025] When transmitted light is incident on SPDC crystal one in the reference cavity, SPDC crystal one converts it into down-converted photons. The down-converted photons include a signal light and an idler light. The signal light and the idler light are then injected into SPDC crystal two, where SPDC crystal two converts it into two signal lights and two idler lights. That is, the down-converted photons from the two SPDC crystals contain signal photon pairs and idler photon pairs. The signal photon pairs and idler photon pairs interfere with each other and obtain interference patterns.

[0026] After being reflected by the mirror, the reflected light is incident on the SPDC crystal three in the measurement cavity. The SPDC crystal three converts it into down-converted photons, which include a signal light and an idler light. The signal light and the idler light are then injected into the SPDC crystal four, which converts them into two signal lights and two idler lights. That is, the down-converted photons from the two SPDC crystals contain signal photon pairs and idler photon pairs. The signal photon pairs and idler photon pairs interfere with each other and obtain interference patterns.

[0027] Downconversion photons emitted from the reference cavity are filtered out by a filter to remove the pump light, and then pass through a focusing lens before being incident on a beam splitter. The light transmitted through the beam splitter is coupled and collimated by a laser collimator.

[0028] Down-conversion photons emitted from the measurement cavity are filtered out by filter two to remove pump light, and then incident on beam splitter two after passing through focusing lens two; the light transmitted through beam splitter two is coupled and collimated by laser collimator two;

[0029] Laser collimator one and laser collimator two are both connected to laser collimator three via optical fibers. The light emitted from laser collimator one and laser collimator two is transmitted in the optical fibers and coupled together into laser collimator three. After being collimated by laser collimator three, the laser light is incident on a CCD camera. The interference patterns obtained through the reference cavity and the interference patterns obtained through the measurement cavity are both detected and received by the CCD camera. The CCD camera transmits the two interference patterns to a computer, which processes and analyzes the interference patterns to obtain the concentration value of the gas to be measured.

[0030] The light reflected by beam splitter one and the light reflected by beam splitter two are received by photodetector one and photodetector two, respectively. After photoelectric conversion, photodetector one and photodetector two generate two electrical signals, which are then transmitted to frequency counters. The frequency counters transmit the two electrical signals to a computer, which calculates and analyzes the interference beat frequency before and after inflation based on the two electrical signals, thereby obtaining the gas refractive index value.

[0031] Furthermore, the gas to be tested is introduced through an inflation assembly; the inflation assembly includes: a vacuum pump group, valve one, an environmental sensor, a gas cylinder, a liquid nitrogen cold trap, and valve two;

[0032] The vacuum chamber is equipped with an exhaust port and an inlet port that communicate with its inner cavity. The exhaust port is connected to a vacuum pump unit via an exhaust pipe, and the inlet port is connected to a gas cylinder via an inlet pipe. The exhaust pipe is equipped with a valve and an environmental sensor, and the inlet pipe is equipped with a liquid nitrogen cold trap and a valve. The vacuum pump unit is used to evacuate the vacuum chamber; the liquid nitrogen cold trap is used to remove impurities; and the environmental sensor is used to detect the pressure, humidity, and temperature parameters inside the vacuum chamber.

[0033] During measurement, the vacuum chamber is first evacuated using a vacuum pump unit. Once the set vacuum level is reached inside the vacuum chamber, the gas cylinder is opened, allowing the gas to be measured to enter the vacuum chamber through the inlet.

[0034] Furthermore, this also includes atomic clocks, which are used to stabilize the frequency of quantum light sources.

[0035] Beneficial effects:

[0036] (1) As a new type of light source, quantum light source plays an increasingly important role in the application of optical quantum technology due to its unique properties and potential. Quantum light source has extremely high sensitivity and accuracy, which makes it have great application prospects in the field of gas detection.

[0037] Therefore, this invention provides a method and apparatus for simultaneously measuring gas refractive index and gas concentration based on a quantum light source. Utilizing the characteristics of a quantum light source, it enables simultaneous measurement of gas refractive index and gas concentration, significantly improving the measurement accuracy. Due to the unique quantum effect and high sensitivity of the quantum light source, it can more accurately capture the scattering and absorption of light by gas molecules, thereby achieving precise measurement of gas properties. This technology enables rapid simultaneous measurement of gas refractive index and gas concentration. Traditional measurement methods often require separate measurements of refractive index and concentration, which are time-consuming and complex. However, the simultaneous measurement technology based on a quantum light source can acquire information on two parameters simultaneously in a single measurement process, enabling precise measurement of multiple parameters, greatly improving measurement efficiency. It is expected to play a greater role in the field of gas detection and provide strong support for the development of related fields.

[0038] (2) When the measuring device of the present invention performs measurement, it first uses a vacuum pump group to evacuate the vacuum chamber. After the vacuum chamber reaches the set vacuum level, the gas cylinder is opened so that the gas to be measured enters the vacuum chamber from the air inlet. This can ensure the purity of the gas to be measured in the vacuum chamber and improve the accuracy of the measurement data of the gas to be measured.

[0039] (3) The measuring device of the present invention also includes an atomic clock, which is used to stabilize the frequency of the quantum light source and can provide a highly stable frequency reference for the quantum light source. Attached Figure Description

[0040] Figure 1 This is a structural diagram of the device of the present invention;

[0041] Figure 2 This is a structural diagram of the reference cavity / measuring cavity of the present invention;

[0042] Among them, 01-Quantum light source; 02-Atomic clock; 03-Collimating lens; 04-Optical isolator; 05-Waveplate; 06-Beam splitter prism; 07-Reference cavity; 08-Filter 1; 09-Focusing lens 2; 010-Reflector; 011-Measuring cavity; 012-Filter 2; 013-Focusing lens 2; 014-Beam splitter 1; 015-Laser collimator 1; 016-Beam splitter 2; 017-Laser collimator 2; 018-Laser collimator 3; 019- CCD camera; 020-Photodetector 1; 021-Photodetector 2; 022-Frequency meter; 023-Computer; 024-Vacuum pump assembly; 025-Valve 1; 026-Environmental sensor; 027-Ejector port; 028-Gas cylinder; 029-Liquid nitrogen cold trap; 030-Valve 2; 031-Inlet; 032-Vacuum chamber; 071-SPDC crystal 1; 072-SPDC crystal 2; 073-Signal photon pair; 074-Idle photon pair. Detailed Implementation

[0043] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0044] Example 1:

[0045] This embodiment provides a method for simultaneously measuring the refractive index and concentration of a gas based on a quantum light source. The specific steps of this method are as follows:

[0046] Step 1: The entangled light (or compressed light) emitted by the quantum light source is collimated, optically isolated, and polarization-state converted. After being split, it is incident on the reference cavity and the measurement cavity respectively. Both the reference cavity and the measurement cavity are composed of two SPDC crystals (i.e., spontaneous parametric down-conversion crystals) arranged in parallel. Both the reference cavity and the measurement cavity are placed inside a vacuum chamber. During operation, the vacuum chamber is filled with the gas to be measured. The two SPDC crystals in the reference cavity and the two SPDC crystals in the measurement cavity have the same thickness, but the distance between the two SPDC crystals in the reference cavity and the closest distance between the two SPDC crystals in the measurement cavity are different.

[0047] Step two: The laser beams emitted from the reference cavity and the measurement cavity are filtered to remove the pump light and then focused before being incident on the beam splitter. The laser beams after passing through the beam splitter are split into transmitted light and reflected light. The two transmitted beams are detected and received by a CCD camera, and their interference patterns are analyzed to obtain the concentration value of the gas to be measured. The two reflected beams are detected and received by a frequency meter, and the refractive index value of the gas to be measured is obtained by analyzing the beat frequency of the dual cavities before and after the gas to be measured is filled into the vacuum chamber.

[0048] In step one, see appendix. Figure 2 Both the reference cavity and the measurement cavity consist of two SPDC crystals. The traditional linear crystals (such as beam splitters BS or polarizing beam splitters PBS) are replaced by two SPDC crystals. When an entangled (or compressed) beam of light emitted from the quantum light source is incident on the first SPDC crystal, the first SPDC crystal converts the entangled (or compressed) beam of light into downconverted photons, which include a signal beam and an idler beam. Then, the signal beam and the idler beam are injected into the second SPDC crystal, which converts them into two signal beams and two idler beams. The downconverted photons from the two SPDC crystals interfere and obtain an interference pattern.

[0049] In step two, the specific process of obtaining the concentration value of the gas to be measured based on the interference pattern is as follows:

[0050] Since the interference mode of the signal light is determined by the total phase obtained from the signal light, idler light, and pump light, in a nonlinear interferometer composed of two SPDC crystals, the closest distance between the two SPDC crystals with a thickness of L is L. m The SPDC crystal was configured to generate signal light and idler light in different spectral ranges, and the interference pattern was detected and received by a CCD camera; the interference pattern of the signal light is represented as follows:

[0051]

[0052] In the formula, I s λ is the intensity of the signal light. s Let θ be the wavelength of the signal light. s The divergence angle of the signal light. The transmittance of the medium to the amplitude of the idler frequency light and δ is the absorption coefficient of the gas to be measured; δ is the total phase obtained from the signal light, idler light, and pump light; δ m Because of the difference between L before and after inflation (i.e., when the vacuum chamber is filled with the gas to be tested) m The phase change is caused by the change in ; sinc is the sigma function;

[0053] The absorption coefficient of the gas to be measured can be obtained from formula (1). Based on the absorption coefficient of the gas to be measured The concentration of the gas to be measured can be obtained by relating it to the concentration of the gas being measured. The formula for calculating the concentration of the gas to be measured is as follows:

[0054]

[0055] In the formula, c is the concentration of the gas to be measured, T is the temperature of the gas to be measured, K′ is a constant, p is atmospheric pressure, and ξ is the water vapor content factor.

[0056] The calculation of the concentration value of the gas to be measured can be performed using the signal light generated by the two SPDC crystals in the reference cavity or the signal light generated by the two SPDC crystals in the measurement cavity, and the calculation results are the same.

[0057] In step two, the specific process of obtaining the refractive index value of the gas under test based on the beat frequency of the two cavities before and after the gas to be tested is filled into the vacuum chamber (i.e., the frequency difference between the measuring cavity frequency and the reference cavity frequency) is as follows:

[0058] First, measure the beat frequency of the dual cavities (i.e., the measuring cavity and the reference cavity) under high vacuum and the initial frequency of the laser under high vacuum. Then, measure the beat frequency of the dual cavities when they are filled with a gas under a certain pressure. The formula for calculating the refractive index n of the gas under test is as follows:

[0059]

[0060] In the formula, v r v is the initial frequency of the laser under high vacuum; beati The pre-inflation dual-chamber beat frequency (i.e., the frequency of the measuring chamber before inflation minus the frequency of the reference chamber); v beatf The frequency of the dual-cavity beat after inflation (i.e., the frequency of the measuring cavity minus the frequency of the reference cavity after inflation); Δm is the change in the longitudinal mode of the laser before and after inflation; v FSR The free spectral range is given, Δp is the change in pressure of the gas to be measured, and K is the bulk modulus of the SPDC crystal material.

[0061] Example 2:

[0062] This embodiment, based on Embodiment 1, provides a device for simultaneous measurement of gas refractive index and concentration using a quantum light source. (See attached diagram.) Figure 1The device includes: a quantum light source 01, an atomic clock 02, a collimating lens 03, an optical isolator 04, a waveplate 05, a beam splitter 06, a reference cavity 07, a first filter 08, a first focusing lens 09, a mirror 010, a measuring cavity 011, a second filter 012, a second focusing lens 013, a first beam splitter 014, a first laser collimator 015, a second beam splitter 016, a second laser collimator 017, a third laser collimator 018, a CCD camera 019, a first photodetector 020, a second photodetector 021, a frequency counter 022, a computer 023, and a vacuum chamber 032.

[0063] The vacuum chamber 032 is filled with the gas to be tested at a certain pressure;

[0064] Both the reference cavity 07 and the measuring cavity 011 are placed inside the vacuum chamber 032; the reference cavity consists of two parallel SPDC crystals, SPDC crystal 071 and SPDC crystal 072; the measuring cavity 011 consists of two parallel SPDC crystals, SPDC crystal 3 and SPDC crystal 4; the thicknesses of SPDC crystal 071, SPDC crystal 072, SPDC crystal 3, and SPDC crystal 4 are equal; the closest distance between SPDC crystal 071 and SPDC crystal 072 is different from the closest distance between SPDC crystal 3 and SPDC crystal 4.

[0065] The quantum light source 01 generates entangled light (or compressed light), and the atomic clock 02 is used to stabilize the frequency of the quantum light source 01, providing a highly stable frequency reference for the quantum light source 01.

[0066] The laser generated by the quantum light source 01 is collimated by the collimating lens 03 and then passes through the optical isolator 04. The emitted light is polarized by the wave plate 05 and then incident on the beam splitter 06 to split the light, forming transmitted light and reflected light.

[0067] When transmitted light is incident on SPDC crystal 071 in reference cavity 07, SPDC crystal 071 converts it into down-converted photons. The down-converted photons include a signal light and an idler light. The signal light and the idler light are then injected into SPDC crystal 072, which converts them into two signal lights and two idler lights. That is, the down-converted photons from the two SPDC crystals contain a signal photon pair 073 and an idler photon pair 074. The signal photon pair 073 and the idler photon pair 074 interfere with each other and obtain interference patterns.

[0068] After being reflected by mirror 010, the reflected light is incident on SPDC crystal three in measurement cavity 011. SPDC crystal three converts it into down-converted photons, which include a signal light and an idler light. The signal light and the idler light are then injected into SPDC crystal four, which converts it into two signal lights and two idler lights. That is, the down-converted photons from the two SPDC crystals contain signal photon pairs and idler photon pairs. The signal photon pairs and idler photon pairs interfere with each other and obtain interference patterns.

[0069] Down-conversion photons emitted from reference cavity 07 are filtered out by filter 08 to remove pump light, and then pass through focusing lens 09 before being incident on beam splitter 014; the light transmitted through beam splitter 014 is coupled and collimated by laser collimator 015.

[0070] Down-conversion photons emitted from measurement cavity 011 are filtered by filter 2012 to remove pump light, and then pass through focusing lens 2013 before being incident on beam splitter 2016; the light transmitted through beam splitter 2016 is coupled and collimated by laser collimator 2017;

[0071] Laser collimator 1 (015) and laser collimator 2 (017) are both connected to laser collimator 3 via optical fiber. The light emitted from laser collimator 1 (015) and laser collimator 2 (017) is transmitted in the optical fiber and coupled into laser collimator 3 (018). After being collimated by laser collimator 3 (018), the laser light is incident on CCD camera 019. The interference patterns obtained through reference cavity 07 and measurement cavity 011 are both detected and received by CCD camera 019. CCD camera 019 transmits the two interference patterns to computer 023, which processes and analyzes the interference patterns to obtain the concentration value of the gas to be measured.

[0072] The light reflected by beam splitter 1 014 and the light reflected by beam splitter 2 016 are received by photodetector 1 020 and photodetector 2 021, respectively. After photoelectric conversion, photodetector 1 020 and photodetector 2 021 generate two electrical signals, which are then transmitted to frequency counter 022. Frequency counter 022 transmits the two electrical signals to computer 023. Computer 023 calculates and analyzes the interference beat frequency before and after inflation based on the two electrical signals, and then obtains the gas refractive index value.

[0073] In this embodiment, the gas to be tested is introduced through an inflation assembly; the inflation assembly includes: a vacuum pump group 024, a valve one 025, an environmental sensor 026, a gas cylinder 028, a liquid nitrogen cold trap 029, and a valve two 030;

[0074] The vacuum chamber 032 is equipped with an exhaust port 027 and an inlet port 031 communicating with its inner cavity. The exhaust port 027 is connected to the vacuum pump assembly 024 via an exhaust pipe, and the inlet port 031 is connected to the gas cylinder 028 via an inlet pipe. The exhaust pipe is equipped with a valve 025 and an environmental sensor 026, and the inlet pipe is equipped with a liquid nitrogen cold trap 029 and a valve 030. The vacuum pump assembly 024 is used to evacuate the vacuum chamber 032 and consists of a mechanical pump, a molecular pump, and an ion pump. The mechanical pump is used to achieve a rough vacuum, the molecular pump is used to further evacuate and increase the vacuum level, and the ion pump is used to maintain the vacuum level. The liquid nitrogen cold trap 029 is used to remove impurities. The environmental sensor 026 is used to detect the pressure inside the vacuum chamber 032.

[0075] During measurement, vacuum pump unit 024 is first used to evacuate vacuum chamber 032. During evacuation, valve 1 025 is opened, and environmental sensor 026 is used to detect the pressure inside vacuum chamber 032. The gas inside vacuum chamber 032 is discharged from the exhaust port 027. When the vacuum chamber 032 reaches the required vacuum level, gas cylinder 028 is opened, and liquid nitrogen cold trap 029 is opened. Liquid nitrogen cold trap 029 removes impurities. Valve 2 030 is opened, and finally the gas to be measured enters vacuum chamber 032 from the inlet 031.

[0076] In summary, the above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for simultaneous measurement of gas refractive index and concentration based on a quantum light source, characterized in that, The specific steps of this method are as follows: Step 1: The entangled or compressed light emitted by the quantum light source is collimated, optically isolated, and polarization-state converted. After being split, it is incident on the reference cavity and the measurement cavity, respectively. Both the reference cavity and the measurement cavity are composed of two SPDC crystals arranged in parallel, and both are placed inside a vacuum chamber. During operation, the vacuum chamber is filled with the gas to be measured. The two SPDC crystals in the reference cavity and the two SPDC crystals in the measurement cavity have the same thickness, but the distance between the two SPDC crystals in the reference cavity and the closest distance between the two SPDC crystals in the measurement cavity are different. When a beam of entangled or compressed light emitted by the quantum light source is incident on the first SPDC crystal, the first SPDC crystal converts the beam of entangled or compressed light into down-converted photons, which include a signal beam and an idler beam. Then, the signal beam and the idler beam are injected into the second SPDC crystal, converting them into two signal beams and two idler beams. The down-converted photons from the two SPDC crystals interfere and obtain an interference pattern. Step two: The laser beams emitted from the reference cavity and the measurement cavity are filtered to remove the pump light and then focused before being incident on the beam splitter. The laser beams after passing through the beam splitter are split into transmitted light and reflected light. The two transmitted beams are detected and received by a CCD camera, and their interference patterns are analyzed to obtain the concentration value of the gas to be measured. The two reflected beams are detected and received by a frequency meter, and the refractive index value of the gas to be measured is obtained by analyzing the beat frequency of the dual cavities before and after the gas to be measured is filled into the vacuum chamber.

2. The method for simultaneous measurement of gas refractive index and concentration based on a quantum light source as described in claim 1, characterized in that, In step two, the specific process of obtaining the concentration value of the gas to be measured based on the interference pattern is as follows: The closest distance between two SPDC crystals of thickness L is The interference pattern is detected and received by a CCD camera; the interference pattern of the signal light is represented as follows: Formula (1) In the formula, The intensity of the signal light. The wavelength of the signal light. The divergence angle of the signal light. The amplitude transmittance of the medium to idler frequency light and , The absorption coefficient of the gas to be measured is denoted as . The total phase obtained from the signal light, idler light, and pump light; Because of the inflation before and after The phase change caused by the change; The absorption coefficient of the gas to be measured can be obtained from formula (1). Based on the absorption coefficient of the gas to be measured The concentration of the gas to be measured can be obtained by relating it to the concentration of the gas being measured. The formula for calculating the concentration of the gas to be measured is as follows: Formula (2) In the formula, The concentration value of the gas to be measured. The temperature of the gas to be measured. It is a constant. Atmospheric pressure The factor is water vapor content.

3. A method for simultaneous measurement of gas refractive index and concentration based on a quantum light source as described in claim 1 or 2, characterized in that, In step two, the specific process of obtaining the refractive index value of the gas to be tested based on the beat frequency of the dual chamber before and after the gas to be tested is filled into the vacuum chamber is as follows: First, measure the beat frequency of the dual cavities when they are in high vacuum and the initial frequency of the laser under high vacuum. Then, measure the beat frequency of the dual cavities when they are filled with the gas to be tested. Then, determine the refractive index of the gas to be tested. The calculation formula is expressed as: Formula (3) In the formula, The initial frequency of the laser under high vacuum; For double-chamber beat frequency before inflation; This refers to the dual-chamber beat frequency after inflation; This represents the change in the longitudinal mode of the laser before and after inflation; For the free spectral range, The change in pressure of the gas to be measured is... This is the bulk modulus of the SPDC crystal material.

4. A device for simultaneously measuring the refractive index and concentration of a gas based on a quantum light source, characterized in that, The device includes: a quantum light source, a collimating lens, an optical isolator, a waveplate, a beam splitter, a reference cavity, a filter I, a focusing lens I, a reflector, a measuring cavity, a filter II, a focusing lens II, a beam splitter I, a laser collimator I, a beam splitter II, a laser collimator II, a laser collimator III, a CCD camera, a photodetector I, a photodetector II, a frequency counter, a computer, and a vacuum chamber; The vacuum chamber is filled with the gas to be tested; Both the reference cavity and the measurement cavity are placed inside the vacuum chamber; the reference cavity consists of two SPDC crystals arranged side by side, SPDC crystal one and SPDC crystal two; the measurement cavity consists of two SPDC crystals arranged side by side, SPDC crystal three and SPDC crystal four; the thicknesses of SPDC crystal one, SPDC crystal two, SPDC crystal three and SPDC crystal four are equal; the closest distance between SPDC crystal one and SPDC crystal two is different from the closest distance between SPDC crystal three and SPDC crystal four; The quantum light source generates entangled or compressed light. The entangled or compressed light is collimated by a collimating lens and then passes through an optical isolator. The emitted light undergoes polarization state conversion by a waveplate and is then incident on a beam splitter to split the light, forming transmitted light and reflected light. When transmitted light is incident on SPDC crystal one in the reference cavity, SPDC crystal one converts it into down-converted photons. The down-converted photons include a signal light and an idler light. The signal light and the idler light are then injected into SPDC crystal two, where SPDC crystal two converts it into two signal lights and two idler lights. That is, the down-converted photons from the two SPDC crystals contain signal photon pairs and idler photon pairs. The signal photon pairs and idler photon pairs interfere with each other and obtain interference patterns. After being reflected by the mirror, the reflected light is incident on the SPDC crystal three in the measurement cavity. The SPDC crystal three converts it into down-converted photons, which include a signal light and an idler light. The signal light and the idler light are then injected into the SPDC crystal four, which converts them into two signal lights and two idler lights. That is, the down-converted photons from the two SPDC crystals contain signal photon pairs and idler photon pairs. The signal photon pairs and idler photon pairs interfere with each other and obtain interference patterns. Downconversion photons emitted from the reference cavity are filtered out by a filter to remove the pump light, and then pass through a focusing lens before being incident on a beam splitter. The light transmitted through the beam splitter is coupled and collimated by a laser collimator. Down-conversion photons emitted from the measurement cavity are filtered out by filter two to remove pump light, and then incident on beam splitter two after passing through focusing lens two; the light transmitted through beam splitter two is coupled and collimated by laser collimator two; Laser collimator one and laser collimator two are both connected to laser collimator three via optical fibers. The light emitted from laser collimator one and laser collimator two is transmitted in the optical fibers and coupled together into laser collimator three. After being collimated by laser collimator three, the laser light is incident on a CCD camera. The interference patterns obtained through the reference cavity and the interference patterns obtained through the measurement cavity are both detected and received by the CCD camera. The CCD camera transmits the two interference patterns to a computer, which processes and analyzes the interference patterns to obtain the concentration value of the gas to be measured. The light reflected by beam splitter one and the light reflected by beam splitter two are received by photodetector one and photodetector two, respectively. After photoelectric conversion, photodetector one and photodetector two generate two electrical signals, which are then transmitted to frequency counters. The frequency counters transmit the two electrical signals to a computer, which calculates and analyzes the interference beat frequency before and after inflation based on the two electrical signals, thereby obtaining the gas refractive index value.

5. The device for simultaneous measurement of gas refractive index and concentration based on a quantum light source as described in claim 4, characterized in that, The gas to be tested is introduced through an inflation assembly; the inflation assembly includes: a vacuum pump set, valve one, an environmental sensor, a gas cylinder, a liquid nitrogen cold trap, and valve two. The vacuum chamber is equipped with an exhaust port and an inlet port that communicate with its inner cavity. The exhaust port is connected to a vacuum pump unit via an exhaust pipe, and the inlet port is connected to a gas cylinder via an inlet pipe. The exhaust pipe is equipped with a valve and an environmental sensor, and the inlet pipe is equipped with a liquid nitrogen cold trap and a valve. The vacuum pump unit is used to evacuate the vacuum chamber; the liquid nitrogen cold trap is used to remove impurities; and the environmental sensor is used to detect the pressure, humidity, and temperature parameters inside the vacuum chamber. During measurement, the vacuum chamber is first evacuated using a vacuum pump unit. Once the set vacuum level is reached inside the vacuum chamber, the gas cylinder is opened, allowing the gas to be measured to enter the vacuum chamber through the inlet.

6. The device for simultaneous measurement of gas refractive index and concentration based on a quantum light source as described in claim 4, characterized in that, It also includes atomic clocks, which are used to stabilize the frequency of quantum light sources.

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