A dual-comb and single-photon counting based optical spectrum measurement system and method

Abstract

A spectral measurement system and method based on dual optical combs and single-photon counting belongs to the field of optical precision measurement. The spectral measurement system of this invention includes two optical frequency combs with a small repetition rate difference (first and second), a first beam splitter, a second beam splitter, a first beam combiner, a second beam combiner, a coaxial transceiver system, a single-photon detector, a single-photon counter, a photodetector, and a data acquisition and processing module. This invention utilizes dual optical comb technology to obtain two time-domain amplified interference signals—a measurement light and a reference light—through optical asynchronous sampling. The measurement light is used for gas spectral detection, while the reference light serves as both a reference spectrum and a timing start signal for the single-photon counter. The single-photon detector and single-photon counter enable long-distance, non-cooperative target gas spectral measurement, obtaining the amplified time-domain interference signal from the measurement optical path. Fourier transform is used to extract the absorption spectrum information of the measured gas, thereby achieving high-precision spectral measurement of long-distance, non-cooperative targets.

Description

Technical Field

[0001] This invention belongs to the field of optical precision measurement and relates to a spectral measurement system and method based on dual optical combs and single photon counting. Background Technology

[0002] Long-distance, high-precision spectroscopic measurements are crucial for detecting gas leaks in large oil and gas pipelines and for detecting hazardous gases over a wide area. An optical frequency comb typically refers to a mode-locked pulsed laser with precise time-frequency domain control. In the time domain, an optical frequency comb consists of a sequence of time-domain pulses with equal time intervals, while in the frequency domain, it appears as a series of frequency comb teeth with completely equal frequency intervals. Optical frequency combs can simultaneously generate millions of optical frequency comb teeth with defined optical frequencies, thus offering significant advantages in spectroscopic measurements. However, applying a single optical frequency comb to spectral measurement and analysis still relies on traditional spectroscopic analysis methods because high-frequency optical signals up to THz cannot be directly obtained through photodetectors. This greatly limits the application expansion of optical frequency combs. The development of dual-comb spectroscopic measurement technology solves this problem. Dual-comb spectroscopic measurement technology is a novel optical detection technology developed based on optical frequency comb technology. The overlapping optical frequency components of two optical frequency combs are down-converted through beat frequency conversion to form an RF comb with a repetition frequency of Δfrep. This allows for rapid measurement directly through a photodetector, offering unparalleled advantages in measurement speed. Compared to traditional Fourier transform infrared spectrometers, dual-comb spectral measurement technology is no longer limited by displacement-type scanning detection structures. The accuracy of its measurement results is determined solely by the properties of the dual-comb light source itself, resulting in faster measurement speed and higher measurement efficiency. However, existing dual-comb spectral measurements place the gas to be measured in the measurement optical path. This path requires a cooperative target, such as a pyramid or mirror, to ensure echo energy. Frequency down-conversion is achieved through asynchronous optical sampling of the local oscillator light, which is then detected and collected by the detector. The spectral absorption change in the measurement optical path is compared with that of the reference light to calculate the gas information. This method requires a cooperative target to maintain the echo energy of the measurement light. Furthermore, in the absence of a cooperative target, to maintain energy matching, the local oscillator light and the measurement light can be combined before spectral measurement, but this results in significant energy loss in the received light and a shorter measurement distance. Therefore, in scenarios where it is impossible to install a cooperative target at a long distance to ensure the echo energy for spectral measurement, such as gas leak detection in large oil and gas pipelines and range-based hazardous gas detection, the existing dual-comb spectral measurement technology is not applicable.

[0003] Single-photon detectors are highly sensitive and capable of detecting weak signals at the photon level. However, unlike ordinary photodetectors, they can only output a voltage signal to record whether a photon has been collected and cannot directly generate information about the entire pulse shape. Therefore, they cannot be directly used for spectral measurements. By combining a single-photon detector with a single-photon counter and accumulating histograms of multiple pulse cycles, the pulse shape can be recovered. Combined with dual-comb spectral measurement technology, high-precision spectral measurements of long-distance non-cooperative targets can be achieved. Summary of the Invention

[0004] To achieve high-precision spectral measurement of long-distance non-cooperative targets, the present invention aims to provide a spectral measurement system and method based on dual optical combs and single-photon counting. The system utilizes dual optical comb technology to obtain two time-domain amplified interference signals—a measurement light and a reference light—through asynchronous optical sampling. The measurement light is used for gas spectral detection, while the reference light serves as both a reference spectrum and a timing start signal for the single-photon counter. Long-distance non-cooperative target gas spectral measurement is achieved through a single-photon detector and a single-photon counter, obtaining the amplified time-domain interference signal from the measurement optical path. Fourier transform is then used to extract the absorption spectrum information of the measured gas.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] The present invention discloses a spectral measurement system based on dual optical combs and single photon counting, comprising two first and second optical frequency combs with a small repetition rate difference, a first beam splitter, a second beam splitter, a first beam combiner, a second beam combiner, a coaxial transceiver system, a single photon detector, a single photon counter, a photodetector, and a data acquisition and processing module.

[0007] The first optical frequency comb emits pulsed laser light, which is split into laser one and laser two by the first beam splitter. The second optical frequency comb emits pulsed laser light with a slight repetition rate difference from the first optical frequency comb, which is split into laser three and laser four by the second beam splitter. Laser one and laser four are optically asynchronously sampled after passing through the second beam combiner, and then amplified in the time domain to generate the measurement path laser. Laser two and laser three are also optically asynchronously sampled after passing through the first beam combiner, and then amplified in the time domain to generate the reference path laser. The reference path laser passes through a photodetector and outputs time-domain amplified reference path pulse electrical signal one and reference path pulse electrical signal two. Pulse electrical signal one is fed to a single-photon counter to record the start time of histogram accumulation. Reference path pulse electrical signal two is fed to the data acquisition and processing module, and Fourier transform is performed to obtain reference spectrum information. The measurement path laser passes through a coaxial receiver and emitter. The laser system emits light to the gas being measured and to a non-cooperative target. A portion of the laser wavelength in the measurement path reacts with and is absorbed by the gas. The non-cooperative target returns the laser light along the same path, re-entering the coaxial transceiver system and transmitting it to a single-photon detector. The single-photon detector converts the received weak laser light into an electrical signal, which serves as the stopping time. This stopping time is recorded by a single-photon counter. Since the laser light intensity is very weak after reflection from the non-cooperative target, a multi-pulse histogram is accumulated using the single-photon counter to recover the time-domain amplified measurement pulse electrical signal. This measurement pulse electrical signal is input to the data acquisition and processing module, where it undergoes a Fourier transform to obtain the measurement path spectral information. The data acquisition and processing module compares this information to calculate the absorption spectrum of the gas being measured, thereby determining the gas composition.

[0008] A spectral measurement system based on dual optical combs and single-photon counting also includes a pulse shaping module. The pulse shaping module offers two shaping methods: either Pulse Shaping Module One or Pulse Shaping Module Two, both achieving the desired pulse shaping. The reference path laser is an optically asynchronously sampled pulse interference signal. Each pulse interference signal contains multiple sub-pulse peaks, which repeatedly trigger the single-photon counter, causing timing disorder and making it impossible to recover the time-domain interferometric amplified measurement path pulse electrical signal, thus preventing spectral measurement. The pulse shaping module shapes the reference path electrical signal into a stable pulse electrical signal for stable triggering of the single-photon counter.

[0009] The pulse shaping module uses Pulse Shaping Module 1 for pulse shaping. Pulse Shaping Module 1 includes a frequency doubling crystal and a dichroic mirror, located between the first beam splitter and the photodetector. After the reference path laser pulse passes through the frequency doubling crystal, the interference pulse signal with multiple sub-pulse peaks is converted into a single-peak pulse laser. The dichroic mirror separates the reference path laser before frequency doubling, transmits the frequency-doubled reference path pulse laser, and then outputs a stable electrical pulse signal with a single peak after passing through the photodetector, which is used for subsequent single-photon counter stabilization timing.

[0010] The pulse shaping module uses pulse shaping module one for pulse shaping. Pulse shaping module two includes a pulse delay unit, located between the photodetector and the single-photon counter. Its function is to add a dead time after the pulse delay unit is triggered once by setting the pulse width. During the dead time, the pulse delay unit will not respond to other sub-pulse peaks of the interference pulse signal again. By setting the length of the dead time, the situation where the single-photon counter is triggered by multiple peaks in the interference envelope is resolved, ensuring that the single-photon counter is triggered only once for the same pulse interference signal, which is used for subsequent single-photon counter stabilization timing.

[0011] The method of optical asynchronous sampling is as follows: the first optical frequency comb and the second optical frequency comb have a small repetition frequency difference. After the optical pulses of the first optical frequency comb and the second optical frequency comb are combined, due to the existence of the small repetition frequency difference, the second optical frequency comb is asynchronously misaligned with the first optical frequency comb in each cycle. After multiple cycles of asynchronous optical sampling of the second optical frequency comb, the first optical frequency comb is asynchronously sampled and amplified in the time domain.

[0012] The method for recovering the optical path interference signal through multi-cycle accumulation is as follows: Before the pulsed laser is generated, a reference laser path is separated and converted into an electrical signal by a photodetector, which is used as the start time and given to a single-photon counter. The measurement laser path separated from the pulsed laser has a very weak light intensity, only at the photon level, after illuminating a non-cooperative target. The single-photon detector detects a single photon and outputs an electrical signal, which is given to the single-photon counter to record the stop time. Within each pulsed laser cycle, the time value of a returning photon is counted, but there is no information about the complete pulse shape. After histogram accumulation in the time domain over multiple pulse cycles, since the probability of counting photons at the target location is the highest, the shape of the pulsed laser is recovered based on the histogram accumulation result, thus obtaining the multi-cycle accumulation recovery measurement optical path interference signal.

[0013] The optical frequency comb is one of the following: fully locked or dual-comb noise-compensated fiber optic frequency comb, electro-optical comb, or microcavity optical comb.

[0014] The coaxial transceiver system is one of the following: a perforated mirror, a fiber optic circulator, or a polarization beam splitter.

[0015] A spectral measurement method based on dual optical combs and single-photon counting is implemented based on the aforementioned spectral measurement system based on dual optical combs and single-photon counting. The spectral measurement method based on dual optical combs and single-photon counting includes the following steps:

[0016] The first step involves optical asynchronous sampling of the first and second optical frequency combs to generate time-domain amplified optical pulses for the measurement and reference paths. The second step involves the reference path laser's time-domain amplified optical pulse being converted into an electrical signal by a photodetector, which is then divided into reference path pulse signal one and reference path pulse signal two. Reference path pulse signal one serves as the start time for the single-photon counter. The measurement path laser interacts with the gas being measured via a coaxial transceiver system and is received by the single-photon detection system as the stop signal for the single-photon counter. The time-domain amplified interference signal carrying the gas absorption spectrum information is recovered through the accumulation of histograms over multiple pulse periods. The third step involves Fourier transforming the interference signals from the reference and measurement paths to the frequency domain, followed by data processing to extract the gas absorption spectrum information.

[0017] In the third step, the amplitude spectrum signals corresponding to the frequency domains of the reference optical path and the measurement optical path are I1(f) and I2(f), respectively, where f corresponds to the radio frequency after time-domain amplification. According to the definition of absorptivity as shown below, the absorptivity R(f) of the laser emitted by the optical frequency comb after passing through the gas to be measured is:

[0018]

[0019] Beneficial effects:

[0020] 1. This invention discloses a spectral measurement system and method based on dual optical combs and single-photon counting. It utilizes dual optical comb technology to obtain two time-domain amplified interference signals, a measurement light and a reference light, through optical asynchronous sampling. The measurement light is used for gas spectral detection, while the reference light serves as both a reference spectrum and a timing start signal for a single-photon counter. The system achieves long-distance non-cooperative target gas spectral measurement through a single-photon detector and a single-photon counter, obtaining the amplified time-domain interference signal of the measurement optical path. The system uses Fourier transform to extract the absorption spectrum information of the measured gas, enabling high-precision spectral measurement of long-distance non-cooperative targets.

[0021] 2. This invention discloses a spectral measurement system and method based on dual optical combs and single-photon counting. Before the pulsed laser is generated, a reference laser path is split off and converted into an electrical signal by a photodetector, which is used as the start time for a single-photon counter. The measurement laser path split off from the pulsed laser, due to its extremely weak intensity (only photon level) after illuminating a non-cooperative target, is detected by a single-photon detector, which outputs an electrical signal, which is used by the single-photon counter to record the stop time. After histogram accumulation in the time domain over multiple pulse cycles, since the probability of photon counting is highest at the target location, the shape of the pulsed laser is reconstructed based on the histogram accumulation result, obtaining a multi-cycle accumulated measurement optical path interference signal used to extract the absorption spectrum information of the measured gas. Traditional dual optical comb spectral measurement requires a cooperative target, such as a corner cube reflector, to ensure echo energy. This invention combines time-correlated single-photon counting technology to measure the components of the gas absorbing along the non-cooperative target path. Simultaneously, utilizing the wide-spectral characteristics of the optical comb, multiple gas components can be measured remotely. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of a spectral measurement system based on dual optical combs and single-photon counting;

[0023] Figure 2 This is a schematic diagram illustrating the principle of histogram accumulation of the interference signal after dual-frequency comb amplification via a single-photon counter.

[0024] Among them, 1—first optical frequency comb, 2—second optical frequency comb, 3—first beam splitter, 4—second beam splitter, 5—first beam combiner, 6—first beam combiner, 7—photodetector, 8—coaxial transceiver optical system, 9—single photon detector, 10—single photon counter, and 11—data acquisition and processing module. Detailed Implementation

[0025] To better illustrate the purpose and advantages of the present invention, the invention will be further described below in conjunction with the accompanying drawings and examples.

[0026] Example 1:

[0027] like Figure 1 As shown, this embodiment discloses a spectral measurement system based on dual optical combs and single-photon counting, including two first optical frequency combs 1 and second optical frequency combs 2 with a small repetition rate difference, a first beam splitter 3, a second beam splitter 4, a first beam combiner 5, a second beam combiner 6, a coaxial transceiver system 8, a single-photon detector 9, a single-photon counter 10, a photodetector 7, and a data acquisition and processing module 11.

[0028] The first optical frequency comb 1 emits pulsed laser light with a center wavelength of 1560 nm, a spectral width of 1450 nm to 1680 nm, and a repetition rate of 200 MHz. After passing through the first beam splitter 3, it is split into laser one and laser two. The second optical frequency comb 2 emits pulsed laser light with a slight repetition rate difference of 1 kHz from the first optical frequency comb 1, a repetition rate of 200.1 MHz, a center wavelength of 1560 nm, and a spectral width of 1450 nm to 1680 nm. After passing through the second beam splitter 4, it is split into laser three and laser four. Laser one and laser four, after passing through the second beam combiner, generate asynchronous optical sampling, such as... Figure 2 As shown in a and 2b, the measurement path laser is generated by interferometric amplification in the time domain. Lasers two and three undergo optical asynchronous sampling after passing through the first beam combiner 5, as shown in Figure 2b. Figure 2 As shown in a and 2b, the reference path laser is amplified in the time domain. The reference path laser passes through photodetector 7, outputting a time-amplified reference path pulse signal one and reference path pulse signal two. Pulse signal one is sent to single-photon counter 10 to record the start time of histogram accumulation. Reference path pulse signal two is sent to data acquisition and processing module 11, where it undergoes Fourier transform to obtain reference spectrum information. The measurement path laser is emitted to the measured gas and non-cooperative target via coaxial transceiver optical system 8. A portion of the measurement path laser's wavelength reacts with and is absorbed by the measured gas. The first optical frequency comb 1 and the second optical frequency comb 1... Frequency comb 2 covers the spectral band of 1450nm–1680nm, with corresponding gas absorption peaks of methane at 1653nm, carbon dioxide at 1572nm, and acetylene at 1542nm. The non-cooperative target returns the measured laser beam along its original path to the coaxial transceiver optical system 8, transmitting it to the single-photon detector 9. The single-photon detector 9 converts the received weak measured laser beam into an electrical signal as the stopping time, which is then sent to the single-photon counter 10 to record the stopping time. Because the measured laser beam is very weak after reflection from the non-cooperative target, multi-pulse histogram accumulation is performed by the single-photon counter 10. Figure 2 As shown in Figure c, the time-domain amplified measurement pulse electrical signal of the laser in the measurement path is restored. The measurement pulse electrical signal is input to the data acquisition and processing module 11. After Fourier transform, the absorption spectrum information of methane, carbon dioxide, and acetylene in the measurement path is obtained. After comparison, the data acquisition and processing module 11 calculates the absorption spectrum information of the gas being measured, and then measures the gas composition, including methane, carbon dioxide, and acetylene.

[0029] A spectral measurement system based on dual optical combs and single-photon counting also includes a pulse shaping module. The pulse shaping module offers two shaping methods: either Pulse Shaping Module One or Pulse Shaping Module Two, both achieving the desired pulse shaping. The reference path laser is a pulse interference signal obtained through optical asynchronous sampling. Each pulse interference signal contains multiple sub-pulse peaks, which repeatedly trigger the single-photon counter 10, causing timing disorder and making it impossible to recover the measured path pulse electrical signal after temporal interferometry amplification, thus preventing spectral measurement. The pulse shaping module shapes the reference path electrical signal into a stable pulse electrical signal for stable triggering of the single-photon counter 10.

[0030] The pulse shaping module uses Pulse Shaping Module 1 for pulse shaping. Pulse Shaping Module 1 includes a frequency doubling crystal, a frequency doubling crystal, and a dichroic mirror. The frequency doubling crystal is a periodically polarized potassium titanyl phosphate crystal, abbreviated as PPKTP crystal, which can frequency double the pulsed laser of the first and second optical frequency combs with a center wavelength of 1560nm to a pulsed laser with a center wavelength of 780nm. The frequency doubling crystal and the dichroic mirror are located between the first beam splitter 3 and the photodetector 7. After the reference path laser pulse passes through the frequency doubling crystal, the interference pulse signal with multiple sub-pulse peaks is converted into a pulsed laser with a single peak. The dichroic mirror separates the reference path laser before frequency doubling, transmits the reference path pulsed laser after frequency doubling, and then outputs a stable electrical pulse signal with a single peak after passing through the photodetector 7, which is used for subsequent stable timing by the single-photon counter 10.

[0031] The pulse shaping module uses pulse shaping module one for pulse shaping. Pulse shaping module two includes a pulse delay unit, model DG645, located between photodetector 7 and single-photon counter 10. Its function is to add a dead time of 50ns after the pulse delay unit is triggered once by setting the pulse width. During the 50ns dead time, the pulse delay unit will not respond to other sub-pulse peaks of the interference pulse signal again. By setting the length of the dead time, the situation where the single-photon counter 10 is triggered multiple times by the peaks in the interference envelope is resolved, ensuring that for the same pulse interference signal, the single-photon counter 10 is triggered only once, which is used for subsequent stable timing of the single-photon counter 10.

[0032] like Figure 2 As shown in a and 2b, the method of optical asynchronous sampling is as follows: the first optical frequency comb 1 and the second optical frequency comb have a small repetition rate difference of 1kHz. After the optical pulses of the first optical frequency comb 1 and the second optical frequency comb are combined, due to the existence of the small repetition rate difference of 1kHz, the second optical frequency comb has an asynchronous misalignment with the first optical frequency comb 1 in each cycle. After multiple cycles of asynchronous optical sampling of the second optical frequency comb, the first optical frequency comb 1 is asynchronously sampled and amplified in the time domain. The amplified time domain pulse period is 1 / 1kHz = 1ms, and the amplified pulse frequency is 1kHz.

[0033] like Figure 2 As shown in c, the method for recovering the interference signal of the measurement optical path after multi-cycle accumulation is as follows: Before the pulsed laser is generated, a reference laser path is separated and converted into an electrical signal by the photodetector 7, which is used as the start time and given to the single-photon counter 10; the measurement laser path separated from the pulsed laser has a very weak light intensity after irradiating a non-cooperative target, only at the photon level. The single photon is detected by the single-photon detector 9 and an electrical signal is output, which is given to the single-photon counter 10 to record the stop time. Within each pulsed laser cycle, that is, within 1ms, the time value of a returning photon is counted, but there is no information on the complete pulse shape. After histogram accumulation in the time domain for multiple pulse cycles, for example, 1000 cycles, corresponding to 1s, since the probability of photon counting is highest at the target location, after histogram accumulation within 1s, the interference shape of the amplified pulsed laser is recovered based on the histogram accumulation result, and the multi-cycle accumulation recovery measurement optical path interference signal is obtained.

[0034] The optical frequency comb is one of the following: fully locked or dual-comb noise-compensated fiber optic frequency comb, electro-optical comb, or microcavity optical comb.

[0035] The coaxial transceiver system is one of the following: a perforated mirror, a fiber optic circulator, or a polarization beam splitter.

[0036] A spectral measurement method based on dual optical combs and single-photon counting is implemented based on the aforementioned spectral measurement system based on dual optical combs and single-photon counting. The spectral measurement method based on dual optical combs and single-photon counting includes the following steps:

[0037] The first step involves optical asynchronous sampling of the first optical frequency comb 1 and the second optical frequency comb 2 to generate time-domain amplified optical pulses for the measurement path laser and the reference path laser. The amplified time-domain pulse period is 1 / 1kHz = 1ms, and the amplified pulse frequency is 1kHz. The second step involves the reference path laser time-domain amplified optical pulse being converted into an electrical signal by the photodetector 7, which is then divided into reference path pulse signal one and reference path pulse signal two. Reference path pulse signal one serves as the start time for the single-photon counter 10. The measurement path laser interacts with the measured gases methane, carbon dioxide, and acetylene via a coaxial transceiver system, and the interaction is received by the single-photon detection system as the stop signal for the single-photon counter 10. The time-domain amplified interference signal carrying the gas absorption spectrum information is recovered through the accumulation of histograms over multiple pulse periods. The third step involves Fourier transforming the interference signals from the reference path and the measurement path to the frequency domain, followed by data processing to extract the gas absorption spectrum information, including that of methane, carbon dioxide, and acetylene.

[0038] In the third step, the amplitude spectrum signals corresponding to the frequency domain of the reference optical path and the measurement optical path are I1(f) and I2(f), as shown in the following equations.

[0039]

[0040] Where f corresponds to the radio frequency after time-domain amplification, and its value should be less than half of the repetition rate of the first optical frequency comb 1, corresponding to nΔf, i.e., an integer multiple of the repetition rate difference; δ is the impulse function; E, f, and φ correspond to the electric field intensity, frequency, and initial phase of the optical frequency comb, respectively; p and q correspond to the p-th longitudinal mode of optical comb 1 and the q-th longitudinal mode of optical comb 2, respectively; P and Q are the sets of all longitudinal modes p and q that satisfy the dual-comb optical downsampling condition, respectively; α(f p ) and α(f q R(f) represents the spectral absorbance corresponding to the p-th and q-th longitudinal modes. p -f q The result can be calculated using the following formula.

[0041]

[0042] What we obtain at this point is the absorption rate of the radiation spectrum. Since there is a one-to-one correspondence between the radiation spectrum and the optical spectrum, conventional methods such as comparison with a standard spectral database and ultra-stable continuous laser beat frequency connection can be used to calculate the actual absorption spectrum information.

[0043] The above detailed description further illustrates the purpose, technical solution, and beneficial effects of the invention. It should be understood that the above description is only a specific embodiment of the present invention and is 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 spectral measurement system based on dual optical combs and single-photon counting, characterized in that: It includes two optical frequency combs with a small repetition rate difference, a first beam splitter, a second beam splitter, a first beam combiner, a second beam combiner, a coaxial transceiver system, a single-photon detector, a single-photon counter, a photodetector, and a data acquisition and processing module; The first optical frequency comb emits pulsed laser light, which is split into laser one and laser two by the first beam splitter. The second optical frequency comb emits pulsed laser light with a slight repetition rate difference from the first optical frequency comb, which is split into laser three and laser four by the second beam splitter. Laser one and laser four are optically asynchronously sampled after passing through the second beam combiner, and then amplified in the time domain to generate the measurement path laser. Laser two and laser three are also optically asynchronously sampled after passing through the first beam combiner, and then amplified in the time domain to generate the reference path laser. The reference path laser passes through a photodetector and outputs time-domain amplified reference path pulse electrical signal one and reference path pulse electrical signal two. Pulse electrical signal one is fed to a single-photon counter to record the start time of histogram accumulation. Reference path pulse electrical signal two is fed to the data acquisition and processing module, and Fourier transform is performed to obtain reference spectrum information. The measurement path laser passes through a coaxial receiver and emitter. The laser system emits light to the gas being measured and to a non-cooperative target. A portion of the laser wavelength in the measurement path reacts with and is absorbed by the gas. The non-cooperative target returns the laser light along the same path, re-entering the coaxial transceiver system and transmitting it to a single-photon detector. The single-photon detector converts the received weak laser light into an electrical signal as a stop time, which is then recorded by a single-photon counter. Because the laser light intensity is very weak after reflection from the non-cooperative target, a multi-pulse histogram is accumulated using the single-photon counter to recover the time-domain amplified measurement pulse electrical signal. This measurement pulse electrical signal is input to the data acquisition and processing module, where a Fourier transform is performed to obtain the measurement path spectral information. The data acquisition and processing module compares this information to calculate the absorption spectrum of the gas being measured, thereby determining the gas composition. The system also includes a pulse shaping module, which is used to shape the reference circuit electrical signal into a stable pulse electrical signal for stable triggering of the single-photon counter. The pulse shaping module uses pulse shaping module one to perform pulse shaping; The pulse shaping module includes a frequency doubling crystal and a dichroic mirror, located between the first beam splitter and the photodetector. After the reference laser pulse passes through the frequency doubling crystal, the interference pulse signal with multiple sub-pulse peaks is converted into a pulse laser with a single peak. The dichroic mirror separates the reference laser before frequency doubling, transmits the reference laser pulse after frequency doubling, and then outputs a stable electrical pulse signal with a single peak after passing through the photodetector, which is used for subsequent single-photon counter stabilization timing.

2. The spectral measurement system based on dual optical combs and single-photon counting as described in claim 1, characterized in that: The pulse shaping module uses pulse shaping module one for pulse shaping; pulse shaping module two includes a pulse delay unit, located between the photodetector and the single-photon counter. Its function is to add a dead time after the pulse delay unit is triggered once by setting the pulse width. During the dead time, the pulse delay unit will not respond to other sub-pulse peaks of the interference pulse signal again. By setting the length of the dead time, the situation where the single-photon counter is triggered by multiple peaks in the interference envelope is resolved, ensuring that the single-photon counter is triggered only once for the same pulse interference signal, which is used for subsequent stable timing of the single-photon counter.

3. The spectral measurement system based on dual optical combs and single-photon counting as described in claim 1, characterized in that: The method of optical asynchronous sampling is as follows: the first optical frequency comb and the second optical frequency comb have a small repetition frequency difference. After the optical pulses of the first optical frequency comb and the second optical frequency comb are combined, due to the existence of the small repetition frequency difference, the second optical frequency comb is asynchronously misaligned with the first optical frequency comb in each cycle. After multiple cycles of asynchronous optical sampling of the second optical frequency comb, the first optical frequency comb is asynchronously sampled and amplified in the time domain.

4. The spectral measurement system based on dual optical combs and single-photon counting as described in claim 1, characterized in that: The method for recovering the optical path interference signal through multi-cycle accumulation is as follows: Before the pulsed laser is generated, a reference laser path is separated and converted into an electrical signal by a photodetector, which is used as the start time and given to a single-photon counter. The measurement laser path separated from the pulsed laser has a very weak light intensity after illuminating a non-cooperative target, only at the photon level. The single-photon detector detects a single photon and outputs an electrical signal, which is given to the single-photon counter to record the stop time. After histogram accumulation in the time domain over multiple pulse cycles, since the probability of photon counting is highest at the location with the target, the shape of the pulsed laser is recovered based on the histogram accumulation result, thus obtaining the multi-cycle accumulation recovery measurement optical path interference signal.

5. The spectral measurement system based on dual optical combs and single-photon counting as described in claim 1, characterized in that: The optical frequency comb is one of the following: fully locked or dual-comb noise-compensated fiber optic frequency comb, electro-optical comb, or microcavity optical comb.

6. The spectral measurement system based on dual optical combs and single-photon counting as described in claim 1, characterized in that: The coaxial transceiver system is one of the following: a perforated mirror, a fiber optic circulator, or a polarization beam splitter.

7. A spectral measurement method based on dual optical combs and single-photon counting, implemented based on a spectral measurement system based on dual optical combs and single-photon counting as described in claims 1, 2, 3, 4, 5, or 6, characterized in that: Includes the following steps, In the first step, the first and second optical frequency combs undergo optical asynchronous sampling to generate time-domain amplified optical pulses for the measurement path laser and the reference path laser; The second step involves converting the time-domain amplified optical pulse of the reference path laser into an electrical signal via a photodetector. This signal is then divided into reference path pulse electrical signal one and reference path pulse electrical signal two. Reference path pulse electrical signal one serves as the start time for the single-photon counter. The laser in the measurement path interacts with the gas being measured via a coaxial transceiver system and is received by the single-photon detection system as the stop signal for the single-photon counter. The time-domain amplified interference signal carrying the gas absorption spectrum information is recovered through the accumulation of histograms over multiple pulse periods. The third step involves Fourier transforming the interference signals from the reference path and the measurement path to the frequency domain, followed by data processing to extract the gas absorption spectrum information.

8. The spectral measurement method based on dual optical combs and single-photon counting as described in claim 7, characterized in that: In the third step, the amplitude spectrum signals corresponding to the frequency domains of the reference optical path and the measurement optical path are I1(f) and I2(f), respectively, where f corresponds to the radio frequency after time-domain amplification. According to the definition of absorptivity as shown below, the absorptivity R(f) of the laser emitted by the optical frequency comb after passing through the gas to be measured is:

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