Femtosecond / picosecond CARS gas detection system and method based on quantum-enhanced reception

Abstract

The application discloses a femtosecond / picosecond CARS gas detection system and method based on quantum enhanced receiving, adopts quantum enhanced receiving technology to carry out gas detection on femtosecond / picosecond CARS, adopts a reference gas pool and controls the light sources of a signal arm and a reference arm to be the same and the optical paths to be equal in length, effectively combines the promotion ability of quantum enhanced receiving technology on weak light signal detection, effectively detects the gas with low concentration in a target detection gas pool, and even rare gas, and is expected to break through the detection limit of the existing femtosecond / picosecond CARS technology on gas concentration.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of laser spectrum diagnosis and quantum enhanced reception, and particularly to a femtosecond / picosecond CARS gas detection system and method based on quantum enhanced reception. BACKGROUND

[0002] The coherent anti-Stokes Raman scattering (CARS) signal based on the ultrafast femtosecond / picosecond light source has been proved to be an effective technology for detecting the composition and concentration of gas molecules, due to its advantages such as good coherence, strong directivity and high signal strength similar to laser. Generally, a wide-spectrum femtosecond light source can provide multiple pump and Stokes spectral contributions to a single molecule, greatly enhancing the CARS signal strength. For example, a normal temperature and pressure femtosecond CARS time-resolved spectrum measurement system is proposed in Chinese Patent Application (Publication No. CN101819064A), in which the light beams output by a femtosecond laser are adjusted into three beams and then focused on a sample cell to measure the CARS signal of a single molecule. However, the femtosecond probe light in this scheme limits the spectral resolution of the CARS signal, so that it can only record the CARS signal strength at different delays by scanning the optical delay line to measure the time-resolved CARS signal and identify the sample. Since the time-resolved CARS signal is the time-averaged result after scanning the optical delay line, it greatly limits the sensitivity of concentration detection and the detection ability of low-concentration samples. If a sub-10 fs ultrafast light source is used as the pump / Stokes light, its natural ultra-wideband characteristics can provide Raman resonant frequency components matched with multiple molecules, thereby realizing the simultaneous excitation of multiple gas molecules in Raman resonance. Subsequently, a picosecond light source is used as the probe light to act on the excited molecules, which will generate a CARS signal spectrum in the phase matching direction that can reflect the characteristics of the molecules. For example, A. Bohlin and C. J. Kliewer, J Phys Chem Lett 6(4), 643-649 (2015) used 7 fs pump / Stokes light and 70 ps probe light to realize the measurement of the CARS spectrum of multiple gas molecules with Raman shift ≤4200 cm -1 -1 in a hydrocarbon flame by using a spectrometer and a CCD camera, but the 70 ps probe light pulse width in this scheme determines that it needs a large delay (90 ps) to suppress the anharmonic background noise, so that it can only realize the measurement of the main gas components (about 5%), which limits the measurement ability of low-concentration gas components of this scheme.

[0003] In recent years, quantum-enhanced receiving systems have achieved signal reception beyond the classical detection limit using quantum measurement principles. Through quantum displacement operations, they have achieved error rates beyond the shot noise limit in classical optical communication, improving channel efficiency. For example, in the literature M.V. Jabir, N. Fajar R. Annafianto, I.A. Burenkov, M. Dagenais, A. Battou, and S.V. Polyakov, AVS Quantum Science 5(1) (2023), a specific ratio of signal light and local oscillator light is achieved by using a beam splitter to interfere, and a photon-level detector is used to measure the presence or absence of photon number, thereby achieving high-precision displacement operations and detection of weak photon-level optical signals. Currently, quantum-enhanced receiving systems are mainly used in communication scenarios. However, their detection capabilities for weak optical signals make them advantageous for coupling into femtosecond / picosecond CARS systems, and they are expected to assist in improving the accuracy of gas component and concentration measurements in femtosecond / picosecond CARS systems.

[0004] Existing femtosecond / picosecond CARS gas detection schemes do not combine with quantum-enhanced receiving systems. They mainly rely on spectrometers and CCD cameras to measure spectral signals or time-resolved signals, and then perform parameter optimization with established simulation models to detect components and concentrations, with limited low-concentration detection. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a femtosecond / picosecond CARS gas detection system and method based on quantum-enhanced receiving to further expand the ability of CARS signals to detect low-concentration gas components.

[0006] To solve the above technical problems, the technical solution adopted by the present application is: a femtosecond / picosecond CARS gas detection system based on quantum-enhanced receiving, comprising:

[0007] A first optical path comprising a pump / Stokes light source, a first beam splitter, a first mirror, a first short-wave pass dichroic mirror, a first focusing lens, a first gas cell, a first short-wave pass filter, a first long-wave pass filter, and a third long-wave pass filter arranged in sequence;

[0008] A second optical path comprising a probe light source, a first optical delay stage, a second beam splitter, a second mirror, a second optical delay stage, a second short-wave pass dichroic mirror, a second focusing lens, a second gas cell, a second short-wave pass filter, a third optical delay stage, a second long-wave pass filter, a third short-wave pass filter, a third beam splitter, and a single-photon detector arranged in sequence;

[0009] The part of the pump / Stokes light split by the first beam splitter is split again by the second beam splitter, the part of the pump / Stokes light split by the second beam splitter is reflected by the first short-wave pass dichroic mirror, the light reflected by the first short-wave pass dichroic mirror is reflected by the second short-wave pass dichroic mirror, and the light reflected by the third long-wave pass filter is reflected by the third beam splitter at a ratio of 99%.

[0010] An adjustable optical attenuator is arranged in the optical path between the first short-wave pass filter and the first long-wave pass filter.

[0011] The part of the light reflected by the first short-wave pass filter, the second short-wave pass filter, the second short-wave pass dichroic mirror, the third long-wave pass filter, the third short-wave pass filter, the first long-wave pass filter, and the second long-wave pass filter is collected by the first light beam collector, the second light beam collector, the third light beam collector, the fourth light beam collector, the fifth light beam collector, the sixth light beam collector, and the seventh light beam collector, respectively.

[0012] The pump / Stokes light is a femtosecond light source with a pulse width of <10fs, and the probe light is a picosecond light source with a pulse width of <5ps.

[0013] The first gas cell is filled with the gas to be measured, and the second gas cell is provided with five gas cavities filled with CO2, CO, N2, CH4, and H2, respectively.

[0014] The splitting ratios of the first beam splitter and the second beam splitter are both 50:50.

[0015] The cutoff wavelengths of the first short-wave pass filter and the second short-wave pass filter are both 485nm.

[0016] The cutoff wavelengths of the first long-wave pass filter and the second long-wave pass filter are the same.

[0017] The cutoff wavelengths of the third long-wave pass filter and the third short-wave pass filter are the same.

[0018] The splitting ratio of the third beam splitter is 99:1.

[0019] As an inventive concept, the application also provides a method for gas detection using the above detection system, which comprises: if it is needed to determine whether the to-be-detected gas in the first gas cell contains a certain gas component, the certain gas is filled into the second gas cell; when the CARS signal of the to-be-detected gas in the first gas cell is measured to contain the certain gas component, the single-photon detector does not respond; and when the CARS signal of the to-be-detected gas in the first gas cell is measured to not contain the certain gas component, the single-photon detector responds. Since the single-photon detector has a dark count, a sequence of pump / Stokes light and detection light pulses are sent, and the photon counts measured by the single-photon detector are counted, so as to determine whether the first gas cell contains the certain gas component.

[0020] The application adopts a system design combining femtosecond / picosecond CARS technology and quantum-enhanced receiving detection technology. In terms of femtosecond / picosecond CARS technology, a sub-10 fs ultra-wideband femtosecond light source is used as pump / Stokes light to realize simultaneous excitation of multiple gas molecules, and a <5 ps narrow-band picosecond light source is used as detection light. The detection pulse width can avoid the complication of the measurement process caused by molecular collision effect, and can suppress non-harmonic background noise at a smaller detection light delay, thereby maximizing the measurable CARS signal strength and improving the low-concentration detection capability. More importantly, by using a beam splitter, a dichroic mirror and other optical path structure designs, the pump / Stokes light and the detection light are split into two identical signal light and reference light paths. By using an optical delay table, the optical paths of the pump / Stokes light and the detection light in the signal light and reference light paths are made consistent. By using quantum-enhanced receiving technology, a quantum displacement operation is realized on the weak CARS signal and the strong CARS signal by using a beam splitter, and then a photon-level signal is measured by using a single-photon detector. The scheme of the application is expected to break through the existing detection limit of gas concentration based on femtosecond / picosecond CARS technology.

[0021] Compared with the prior art, the application has the beneficial effects that: the application uses quantum-enhanced receiving technology to carry out gas detection based on femtosecond / picosecond CARS, uses a reference gas cell and controls the light sources of the signal arm and the reference arm to be the same and the optical paths to be equal in length, effectively combines the improvement capability of quantum-enhanced receiving technology for weak light signal detection, and effectively detects a gas with a low concentration or even a rare gas in the target detection gas cell, which is expected to break through the existing detection limit of gas concentration based on femtosecond / picosecond CARS technology. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The structure schematic diagram of the femtosecond / picosecond coherent anti-Stokes Raman scattering gas detection system based on quantum-enhanced receiving provided by the embodiment of the application is shown. DETAILED DESCRIPTION

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] like Figure 1 As shown, this embodiment of the invention provides a femtosecond / picosecond coherent anti-Stokes Raman scattering gas detection scheme based on quantum-enhanced reception. The femtosecond / picosecond CARS gas detection system based on quantum-enhanced reception includes a transmitter, a measurement unit, and a receiver. The transmitter mainly involves the excitation of the CARS signal and includes a pump / Stokes light source, a probe light source, a first optical delay stage, a second optical delay stage, a first beam splitter BS1, a second beam splitter BS2, a first reflector M1, a second reflector M2, a first short-pass dichroic mirror SPDC1, a second short-pass dichroic mirror SPDC2, a first focusing lens FL1, and a second focusing lens FL2.

[0025] The pump / Stokes light source is a femtosecond long-wavelength light source, and the probe light source is a picosecond short-wavelength light source.

[0026] The femtosecond pulsed laser output from the pump / Stokes source is split into two beams by the first beam splitter BS1. The transmitted light component is reflected by the first reflecting mirror M1 and then reflected again by the first short-pass dichroic mirror SPDC1 before being transmitted to the first focusing lens FL1.

[0027] The pump / Stokes light component reflected by the first beam splitter BS1 is split into two beams again by the second beam splitter BS2. The reflected beam is then reflected sequentially by the first short-pass dichroic mirror SPDC1 and the second short-pass dichroic mirror SPDC2 before being transmitted to the second focusing lens FL2. The transmitted beam is reflected by the second mirror M2, transmitted through the second optical delay stage, reflected by the second short-pass dichroic mirror SPDC2, and then collected by the third beam collector BD3.

[0028] The second optical delay stage consists of four mirrors and a stepping stage that controls the translation of the mirrors.

[0029] The picosecond pulse laser output from the detection light source first passes through the first optical delay stage and is then split into two beams by the second beam splitter BS2. The transmitted light component is transmitted through the first short-pass dichroic mirror SPDC1 and then transmitted to the first focusing lens FL1; the reflected light component is reflected by the second reflecting mirror M2, transmitted through the second optical delay stage, transmitted through the second short-pass dichroic mirror SPDC2, and then transmitted to the second focusing lens FL2.

[0030] The first optical delay stage consists of four mirrors and a stepping stage that controls the translation of the mirrors.

[0031] Furthermore, a first gas cell to be detected and a second gas cell providing reference gas are placed between the transmitter and receiver. The pump / Stokes light and probe light components transmitted into the first focusing lens FL1 are jointly focused into the first gas cell to generate a CARS signal; the pump / Stokes light and probe light components transmitted into the second focusing lens FL2 are jointly focused into the second gas cell to generate a CARS signal.

[0032] Furthermore, the receiver mainly involves CARS signal extraction and quantum-enhanced receiver detection module, including a first short-pass filter SPF1, a first beam collector BD1, a second short-pass filter SPF2, a second beam collector BD2, a tunable optical attenuator VOA, a third optical delay stage, a quantum-enhanced receiver detection module, a fourth beam collector BD4, a fifth beam collector BD5, a sixth beam collector BD6, and a seventh beam collector BD7.

[0033] The third optical delay stage consists of four mirrors and a stepping stage that controls the translation of the mirrors.

[0034] Furthermore, the quantum-enhanced receiver detection module includes: a first long-pass filter LPF1, a second long-pass filter LPF2, a third long-pass filter LPF3, a third short-pass filter SPF3, a third beam splitter BS3, and a single-photon detector PD.

[0035] The CARS signal generated by the first gas cell is filtered by the first short-pass filter SPF1 to remove the remaining pump / Stokes light and probe light, and then attenuated by the adjustable optical attenuator VOA before being transmitted to the first and third long-pass filters (LPF1, LPF3). The appropriate cutoff wavelengths of the first and third long-pass filters (LPF1, LPF3) are determined according to the Raman resonant frequency of the target gas. Furthermore, the target gas CARS signal is reflected by the third long-pass filter LPF3 and then transmitted to the third beam splitter BS3.

[0036] The CARS signal generated by the second gas cell is filtered by the second short-pass filter SPF2 to remove the remaining pump / Stokes light and probe light, and then transmitted to the second long-pass filter LPF2 and the third short-pass filter SPF3. The second long-pass filter LPF2 is selected with the same cutoff wavelength as LPF1, and the third short-pass filter SPF3 is selected with the same or similar cutoff wavelength as LPF3. The purpose is to make the third short-pass filter SPF3 transmit the same target gas CARS signal as the third long-pass filter LPF3 reflects.

[0037] A third optical delay stage is set between the second short-pass filter SPF2 and the second long-pass filter LPF2 to adjust the time synchronization of the two CARS optical signals input to the third beam splitter BS3.

[0038] The CARS signal, reflected by the third long-pass filter LPF3 and transmitted by the third short-pass filter SPF3, is transmitted together to the third beam splitter BS3 and undergoes interference and quantum shift operations. The signal after quantum shift is detected by the single-photon detector PD.

[0039] The present invention also provides a method for femtosecond / picosecond CARS gas detection based on quantum enhanced reception, which relies on the above-mentioned device for femtosecond / picosecond CARS gas detection based on quantum enhanced reception, as detailed below:

[0040] The light emitted from the pump / Stokes light source is split into a first transmission component and a first reflection component after passing through the 50:50 first beam splitter M1; the light emitted from the probe light source is also split into a first transmission component and a first reflection component after being transmitted through the first optical delay stage and then through the second beam splitter.

[0041] The first transmitted component of the pump / Stokes light is reflected by the first reflecting mirror M1 and then by the first short-pass dichroic mirror SPDC1. The first transmitted component of the probe light is transmitted through the first short-pass dichroic mirror SPDC1 and collinearly coincides with the pump / Stokes light reflected by the first short-pass dichroic mirror SPDC1. Both are focused by the first focusing lens FL1 onto the first gas cell. By adjusting the first optical delay stage, the two beams of light arriving at the first gas cell overlap in time and need to meet the collinear phase matching condition in space, thereby exciting the gas molecules in the first gas cell and generating the corresponding CARS signal of the gas. The CARS signal generated in this path will be used as the signal arm of the quantum enhancement receiving and detection module, denoted as the signal light.

[0042] The first gas cell contains the unknown gas to be measured.

[0043] The first reflected component of the pump / Stokes light is further divided into a transmitted component and a reflected component after passing through the 50:50 second beam splitter BS2, which are denoted as the second transmitted component and the second reflected component, respectively. The second reflected component of the pump / Stokes light is further reflected sequentially by the first short-pass dichroic mirror SPDC1 and the second short-pass dichroic mirror SPDC2 before being transmitted to the second focusing lens FL2. The second transmitted component of the pump / Stokes light is reflected by the second reflecting mirror M2 and then further reflected by the second short-pass dichroic mirror SPDC2 after passing through the second optical delay stage. Subsequently, it is collected by the third light collector BD3.

[0044] Furthermore, the first reflected component of the probe light is reflected by the second reflecting mirror M2, then transmitted through the second optical delay stage and through the second short-pass dichroic mirror SPDC2. It collinearly coincides with the second reflected component of the pump / Stokes light after being reflected by the first and second short-pass dichroic mirrors (SPDC1, SPDC2). Both are focused by the second focusing lens FL2 onto the second gas cell. Under the condition of collinear phase matching, the gas molecules in the second gas cell are excited to generate a CARS signal. The CARS signal generated in this path will be used as the reference arm of the quantum enhancement receiving and detection module, and is denoted as the reference light.

[0045] The second gas pool contains gases of known composition, including most gases relevant to applications involving combustion and gasification, such as N2, O2, CO, CO2, CH4, and H2.

[0046] The coherent anti-Stokes Raman scattering signal generated by the first and second gas cells, along with the remaining pump / Stokes light and probe light, are transmitted forward together. The remaining pump / Stokes light and probe light are filtered out by the first and second short-pass filters (SPF1, SPF2), respectively. Since the anti-Stokes light will undergo a blue shift relative to the probe light, i.e., the wavelength is reduced, by reasonably selecting the cutoff wavelength of the first and second short-pass filters (SPF1, SPF2), the coherent anti-Stokes light in both optical paths can be transmitted through, while the remaining pump / Stokes light and probe light are reflected and collected by the first and second beam collectors (BD1, BD2), respectively.

[0047] Furthermore, the signal light is attenuated by the adjustable optical attenuator VOA, and transmitted through the first long-pass filter LPF1 and reflected by the third long-pass filter LPF3 to form the target gas CARS signal light; the signal component transmitted through the third long-pass filter LPF3 is collected by the fourth optical collector BD4.

[0048] The reference light is transmitted through the second long-pass filter LPF2 and the third short-pass filter SPF3, which transmits the same target gas CARS reference light component as the signal arm; the signal component reflected by the third short-pass filter SPF3 is collected by the fifth light collector BD5.

[0049] The first long-pass filter LPF1 and the second long-pass filter LPF2 have the same cutoff wavelength, denoted as the first cutoff wavelength; the third long-pass filter LPF3 and the third short-pass filter SPF3 have the same or similar cutoff wavelengths, denoted as the second cutoff wavelength. These two cutoff wavelengths are used to selectively detect a target molecule. Weak signal light with wavelengths higher than the first cutoff wavelength but lower than the second cutoff wavelength is transmitted through the first long-pass filter LPF1 and reflected by the third long-pass filter LPF3. Strong reference light with wavelengths higher than the first cutoff wavelength but lower than the second cutoff wavelength is transmitted sequentially by the second long-pass filter LPF2 and the third short-pass filter SPF3. The signal light and reference light converge at the third beam splitter BS3 (99:1 ratio), where 99% of the weak signal light is reflected and 1% of the strong reference light is transmitted, forming a quantum-enhanced receiving and detection module.

[0050] Assuming N2 is present in the first gas cell (when an N2 gas sample is placed in the second gas cell), N2 CARS signals will be generated in both the signal and reference beams. The wavelength of the N2 CARS signal is higher than the first cutoff wavelength but lower than the second cutoff wavelength. The CARS signal light generated by the signal arm is attenuated and ultimately reflected by the third long-pass filter LPF3; the strong reference CARS light generated by the reference arm is ultimately transmitted by the third short-pass filter SPF3. By controlling the second optical delay stage, the optical path lengths of the signal and reference beams to the third beam splitter BS3 are made the same, meaning that their phases are the same when they reach the third beam splitter BS3. Subsequently, the two beams are mixed at the beam splitter and interfere at its output, generating a shifted coherent state. When N2 is present in the first gas cell, the signal and reference beams have the same frequency and phase. The shift operation shifts the signal beam to a vacuum state, at which point the single-photon detector does not respond. When there is no N2 in the first gas cell, i.e., the input is a vacuum state, the single-photon detector responds after the shift operation. Therefore, by sending a series of pulsed lasers and counting the single-photon detectors, it is possible to determine whether N2 is present in the first gas pool.

[0051] The transmitter pump / Stokes light uses a femtosecond source with a pulse width <10 fs and a wavelength range of approximately 650-1000 nm; the probe light uses a source with a pulse width <5 ps and a wavelength of 515 nm. The gas to be measured is placed in the first gas cell; five gas chambers are prepared in the second gas cell, respectively filled with CO2, CO, N2, CH4, and H2. The vibrational Raman translations of CO2, CO, N2, CH4, and H2 are 1388 cm⁻¹. -1 2143cm -1 2330cm -1 2917cm -1 4160cm -1 .

[0052] Due to Raman translation It can be represented as:

[0053]

[0054] Where λ0 is the center wavelength of the probe light, and λ is the center wavelength of the Raman signal.

[0055] Therefore, when the probe wavelength is 515 nm, the corresponding center wavelengths of the CARS signal spectra of CO2, CO, N2, and H2 are 480.6 nm, 463.8 nm, 459.8 nm, 447.7 nm, and 424.1 nm, respectively. The CARS signal wavelength of the target molecule will determine the selection of the cutoff wavelength of the filter in the system.

[0056] The pump / Stokes light is split by the first beam splitter BS1. 50% of the pump / Stokes light is transmitted through BS1 and reflected by the first reflecting mirror M1. Subsequently, it is reflected by the first short-pass dichroic mirror SPDC1 (550nm). Another 50% of the pump / Stokes light is reflected by BS1 and then split again at the second beam splitter BS2, so that 25% of the pump / Stokes light is reflected by BS2, and the remaining 25% is transmitted through BS2. The pump / Stokes light reflected by BS2 is then reflected sequentially by SPDC1 and the first short-pass dichroic mirror SPDC2 (550nm) before being transmitted to the second focusing lens FL2. The pump / Stokes light transmitted by BS2 is reflected sequentially by M2 and SPDC2 and then collected by BD3, and is not used as the CARS excitation light component required by the system.

[0057] The probe light, after passing through the first optical delay stage, is split by the second beam splitter BS2. 50% of the probe light, transmitted through BS2, merges with the 50% pump / Stokes light transmitted through BS1 at SPDC1 and propagates collinearly forward. It is then focused into the first gas cell by the first focusing lens FL1, generating a CARS signal. This signal, after being filtered by the first short-pass filter SPF1 to remove the remaining pump / Stokes light and probe light, is attenuated by an adjustable optical attenuator and used as the signal light for the subsequent quantum enhancement receiving and detection module. SPF1 has a 485nm cutoff wavelength to ensure that CARS signals from CO2, CO, N2, CH4, and H2 can all pass through SPF1.

[0058] The remaining 50% of the probe light, after being reflected by BS2 and then again by the second mirror M2, is transmitted through the second optical delay stage and then through SPDC2. This beam merges with the pump / Stokes light reflected by BS2, SPDC1, and SPDC2 and propagates collinearly forward. It is then focused by the second focusing lens FL2 onto the second gas cell, generating a CARS signal. This signal, after being filtered by the second short-pass filter SPF2 to remove the remaining pump / Stokes light and probe light, serves as the reference light for the subsequent quantum enhancement receiver detection module. Similarly, SPF2 uses a 485nm cutoff wavelength to ensure that CARS signals from CO2, CO, N2, CH4, and H2 can all pass through SPF2.

[0059] It is important to note that during the CARS signal generation stage, the first optical delay stage must first be adjusted to synchronize the pump / Stokes beam and probe beam in the signal arm; then, the second optical delay stage must be adjusted to synchronize the probe beam and pump / Stokes beam in the reference path. Finally, the third optical delay stage is adjusted so that the Raman scattering signals generated by the signal arm and the reference arm arrive at BS3 simultaneously to form effective interference, thereby enabling the displacement manipulation of the weak CARS signal beam.

[0060] To determine whether the gas to be tested in the first gas cell contains N2, a gas chamber filled with N2 is placed in the second gas cell. Since the peak value of the N2 CARS signal is at 459.8 nm, a first long-pass filter LPF1 and a second long-pass filter LPF2 with a cutoff wavelength of 458 nm are selected, along with a third long-pass filter LPF3 and a third short-pass filter SPF3 with a cutoff wavelength of 462 nm. This ensures that the CARS signal in the signal arm and reference arm, with wavelengths between 458 and 462 nm, can be transmitted to the third beam splitter BS3. When the CARS signal of the gas to be tested in the first gas cell contains N2, it moves to a vacuum state after a displacement operation with the reference light; at this time, the single-photon detector does not respond. When the gas to be tested in the first gas cell does not contain N2, i.e., the input is a vacuum state, the single-photon detector responds after the displacement operation. The single-photon detector count is recorded by sending a series of pulsed lasers.

[0061] Similarly, a CO-filled gas chamber is placed in the second gas cell. Since the peak CARS signal of CO appears at 463.8 nm, LPF1 and LPF2 with cutoff wavelengths of 462 nm and LPF3 and SPF3 with cutoff wavelengths of 465 nm are selected to ensure that only the CARS signal of the target molecule CO is transmitted to the third beam splitter BS3, and then detected by a single-photon detector. The single-photon detector count is recorded within the same detection time as for N2. The above operation is repeated for other gases such as CO2, CH4, and H2. Finally, by comparing and analyzing the single-photon detector counts under different gas conditions in the second gas cell, the composition and concentration of CO2, CO, N2, CH4, and H2 in the first gas cell can be measured and analyzed.

[0062] Due to the ultra-wideband characteristics of the sub-10 femtosecond pump / Stokes light source, it can simultaneously provide pump and Stokes excitation spectral components of multiple gas molecules. Therefore, when placing a gas chamber filled with different gases at the second gas cell, there is no need to change the light source or adjust the optical path structure.

[0063] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0064] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A femtosecond / picosecond CARS gas detection system based on quantum-enhanced reception, characterized in that, include: The first optical path includes a pump / Stokes light source, a first beam splitter, a first reflector, a first short-pass dichroic mirror, a first focusing lens, a first gas cell, a first short-pass filter, a first long-pass filter, and a third long-pass filter arranged sequentially. The second optical path includes, in sequence, a detection light source, a first optical delay stage, a second beam splitter, a second reflector, a second optical delay stage, a second short-pass dichroic mirror, a second focusing lens, a second gas cell, a second short-pass filter, a third optical delay stage, a second long-pass filter, a third short-pass filter, a third beam splitter, and a single-photon detector. In this process, a portion of the pump / Stokes light split by the first beam splitter is split again by the second beam splitter, a portion of the pump / Stokes light split by the second beam splitter is reflected by the first short-pass dichroic mirror, the light reflected by the first short-pass dichroic mirror is reflected by the second short-pass dichroic mirror, and the light reflected by the third long-pass filter is reflected by the third beam splitter at a ratio of 99%. The first long-pass filter and the second long-pass filter have the same cutoff wavelength; the third long-pass filter and the third short-pass filter have the same cutoff wavelength.

2. The femtosecond / picosecond CARS gas detection system based on quantum-enhanced reception according to claim 1, characterized in that, An adjustable optical attenuator is provided in the optical path between the first short-pass filter and the first long-pass filter.

3. The femtosecond / picosecond CARS gas detection system based on quantum-enhanced reception according to claim 1, characterized in that, The light reflected by the first short-pass filter, the second short-pass filter, the second short-pass dichroic mirror, the third long-pass filter, the third short-pass filter, the first long-pass filter, and the second long-pass filter is collected by the first beam collector, the second beam collector, the third beam collector, the fourth beam collector, the fifth beam collector, the sixth beam collector, and the seventh beam collector, respectively.

4. The femtosecond / picosecond CARS gas detection system based on quantum-enhanced reception according to claim 1, characterized in that, The pump / Stokes light is a femtosecond light source with a pulse width of <10 fs; the probe light is a picosecond light source with a pulse width of <5 ps.

5. The femtosecond / picosecond CARS gas detection system based on quantum-enhanced reception according to claim 1, characterized in that, The first gas cell is filled with the gas to be tested, and the second gas cell is provided with five gas chambers respectively filled with CO2, CO, N2, CH4 and H2.

6. The femtosecond / picosecond CARS gas detection system based on quantum-enhanced reception according to claim 1, characterized in that, The beam splitting ratio of both the first and second beam splitters is 50:

50.

7. The femtosecond / picosecond CARS gas detection system based on quantum-enhanced reception according to claim 1, characterized in that, The cutoff wavelengths of both the first and second short-pass filters are 485 nm.

8. A method for gas detection using the detection system according to any one of claims 1 to 7, characterized in that, The method includes: if it is necessary to determine whether the gas to be tested in the first gas cell contains a certain gas component, the gas is filled into the second gas cell; when the CARS signal of the gas to be tested in the first gas cell contains the gas component, the single-photon detector does not respond; when the CARS signal of the gas to be tested in the first gas cell does not contain the gas component, the single-photon detector responds.

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