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

Abstract

The invention discloses a femtosecond / picosecond CARS gas detection system and method based on quantum enhanced reception, the quantum enhanced reception technology is adopted to carry out femtosecond / picosecond CARS gas detection, a reference gas cell is adopted, and a signal arm and a reference arm are controlled to be the same in light source and equal in light path length. The method effectively combines the improvement capability of the quantum enhanced receiving technology on weak light signal detection, realizes effective detection on low-concentration gas and even rare gas in a target detection gas pool, and is expected to break through the detection limit of the existing femtosecond / picosecond-based CARS technology on gas concentration.

Description

Technical Field

[0001] The present invention relates to the fields of laser spectrum diagnosis and quantum enhanced reception, and in particular to a femtosecond / picosecond CARS gas detection system and method based on quantum enhanced reception. Background Art

[0002] Coherent anti-Stokes Raman scattering (CARS) signals from ultrafast femtosecond and picosecond light sources have been proven to be an effective technique for detecting gas molecular composition and concentration, due to their advantages similar to lasers, such as good coherence, strong directionality, and high signal intensity. Typically, a broadband femtosecond light source can provide multiple pump and Stokes spectral contribution pairs for a single molecule, greatly enhancing the CARS signal intensity. For example, a Chinese patent application (publication number CN101819064A) proposes a femtosecond CARS time-resolved spectroscopy measurement system at room temperature and pressure. This system measures the CARS signal of a single molecule by adjusting the output beam of a femtosecond laser into three beams that are then focused on a sample cell. However, the femtosecond-scale probe light in this scheme limits the spectral resolution of the CARS signal, forcing sample identification to be achieved only by scanning an optical delay line and recording the CARS signal intensity at different delays to obtain a time-resolved CARS signal. Because the time-resolved CARS signal is the time-averaged result of the optical delay line scan, its concentration detection sensitivity and ability to detect low-concentration samples are significantly limited. If a sub-10 fs ultrafast light source is used as pump / Stokes light, its natural ultra-wideband characteristics can provide Raman resonance frequency components that match multiple molecules, thereby achieving simultaneous excitation of Raman resonances of multiple gas molecules. Subsequently, a picosecond light source is used as a probe light to act on the excited molecules, which will produce a CARS signal spectrum that can reflect the molecular characteristics in its phase matching direction. For example, in the literature A. Bohlin and CJ Kliewer, JP Hys Chem Lett 6 (4), 643-649 (2015), a 7 fs pump / Stokes light and a 70 ps probe light were used to achieve Raman shift ≤ 4200 cm in hydrocarbon flames using a spectrometer and a CCD camera. -1 However, the 70ps detection light pulse width in this scheme determines that a larger delay (90ps) is required to suppress the non-resonant background noise, so that it can only measure the main gas components (about 5%), limiting the scheme's ability to measure low-concentration gas components.

[0003] In recent years, quantum-enhanced receiving systems have achieved signal reception beyond the classical detection limit by using quantum measurement principles. Through quantum shift operations, they have achieved bit error rates that exceed the shot noise limit in classical optical communications, thereby improving channel efficiency. For example, in the literature MV Jabir, N. Fajar R. Annafianto, I A Burenkov, M. Dagenais, A. Battou, and S. V. Polyakov, AVS Quantum Science 5(1)(2023), a beam splitter is used to achieve interference between signal light and local oscillator light in a specific ratio, and a photon-level detector is used to measure the number of photons, thereby achieving high-precision shift operations and detection of weak optical signals at the photon level. At present, quantum-enhanced receiving systems are mainly used in communication scenarios. However, their ability to detect weak optical signals gives them the advantage of being coupled into femtosecond / picosecond CARS systems, which is expected to help improve the accuracy of femtosecond / picosecond CARS systems in measuring gas composition and concentration.

[0004] Existing femtosecond / picosecond CARS gas detection solutions do not have measurement solutions combined with quantum enhanced receiving systems. They mainly rely on spectrometers and CCD cameras to measure spectral signals or time-resolved signals, and then optimize parameters through established simulation models to detect components and concentrations. Low-concentration detection is limited. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a femtosecond / picosecond CARS gas detection system and method based on quantum enhanced reception to address the shortcomings of the existing technology, and 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 invention is: a femtosecond / picosecond CARS gas detection system based on quantum enhanced reception, comprising:

[0007] The first optical path includes a pump / Stokes light source, a first beam splitter, a first reflector, 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, which are arranged in sequence;

[0008] The second optical path includes a detection light source, a first optical delay stage, a second beam splitter, a second reflector, 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, which are arranged in sequence;

[0009] Part of the pump / Stokes light split by the first beam splitter is split again by the second beam splitter, 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 provided on the optical path between the first short-wave pass filter and the first long-wave pass filter.

[0011] 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 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.

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

[0013] The first gas pool is filled with the gas to be tested, and the second gas pool is provided with five gas chambers which are filled with CO2, CO, N2, CH4 and H2 respectively.

[0014] The beam 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 485 nm.

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

[0019] As an inventive concept, the present invention also provides a method for gas detection using the above-mentioned detection system. The method includes: if it is necessary to determine whether the gas to be tested in the first gas pool contains a certain gas component, the gas is filled into the second gas pool. When the CARS signal of the gas to be tested in the first gas pool is detected to contain the gas component, the single-photon detector does not respond; when the CARS signal of the gas to be tested in the first gas pool is detected to not contain the gas component, the single-photon detector responds. Because the single-photon detector has a dark count, it is necessary to send a sequence of pump / Stokes light and detection light pulses and calculate the photon counts measured by the single-photon detector to determine whether the first gas pool contains the gas component.

[0020] This system design combines femtosecond / picosecond CARS technology with quantum-enhanced detection. In femtosecond / picosecond CARS, a sub-10fs ultra-broadband femtosecond light source is used as the pump / Stokes light source to simultaneously excite multiple gas molecules, while a narrow-band picosecond light source with a pulse width of less than 5ps is used as the probe light. This probe pulse width not only avoids molecular collision effects that complicate the measurement process, but also suppresses non-resonant background noise at smaller probe light delays, maximizing the measurable CARS signal intensity and improving its low-concentration detection capabilities. More importantly, by utilizing optical path structures such as beam splitters and dichroic mirrors, the pump / Stokes light and probe light are split into two identical signal light and reference light paths. An optical delay stage is designed to make the pump / Stokes light and probe light paths consistent in the signal light and reference light paths. Quantum-enhanced reception technology is used to implement quantum shift operations on one path, which is attenuated into a weak CARS signal, and the other path, which is a strong CARS signal, using a beam splitter. This allows for measurement of photon-level signals using a single-photon detector. The solution of the present invention is expected to break through the existing detection limits of gas concentrations based on femtosecond / picosecond CARS technology.

[0021] Compared with the existing technology, the present invention has the following beneficial effects: the present invention adopts quantum enhanced reception technology to carry out gas detection for femtosecond / picosecond CARS, adopts a reference gas pool and controls the signal arm and the reference arm to have the same light source and the same optical path length, effectively combining the improvement ability of quantum enhanced reception technology for weak light signal detection, and effectively detecting gases with low concentrations in the target detection gas pool, and even rare gases, and is expected to break through the existing detection limit of gas concentration based on femtosecond / picosecond CARS technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A schematic structural diagram of a femtosecond / picosecond coherent anti-Stokes Raman scattering gas detection system based on quantum enhanced reception provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0024] like Figure 1 As shown, an embodiment of the present invention provides a femtosecond / picosecond coherent anti-Stokes Raman scattering gas detection solution based on quantum-enhanced reception. The femtosecond / picosecond CARS gas detection system based on quantum-enhanced reception includes a transmitter, a measuring end, and a receiver. The transmitter mainly involves the excitation of the CARS signal, including 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-wavelength pass dichroic mirror SPDC1, a second short-wavelength 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-wave light source, and the probe light source is a picosecond short-wave light source.

[0026] The femtosecond pulse laser output by the pump / Stokes light source is split into two beams by the first beam splitter BS1. The transmitted light component is reflected by the first reflector M1 and then reflected again by the first short-wave 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 reflected by the first short-wavelength pass dichroic mirror SPDC1 and the second short-wavelength pass dichroic mirror SPDC2 in sequence and then transmitted to the second focusing lens FL2; the transmitted beam is reflected by the second reflector M2, transmitted by the second optical delay stage, reflected by the second short-wavelength pass dichroic mirror SPDC2, and then collected by the third beam dump BD3.

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

[0029] The picosecond pulse laser output by 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-wavelength pass dichroic mirror SPDC1 and then transmitted to the first focusing lens FL1; the reflected light component is reflected by the second reflector M2, transmitted through the second optical delay stage, transmitted through the second short-wavelength pass dichroic mirror SPDC2, and then transmitted to the second focusing lens FL2.

[0030] The first optical delay stage consists of four reflecting mirrors and a stepping stage for controlling the translation of the reflecting mirrors.

[0031] Furthermore, a first gas cell to be detected and a second gas cell providing a reference gas are placed between the transmitting and receiving ends. The pump / Stokes light and probe light components transmitted into the first focusing lens FL1 are co-focused in the first gas cell, generating a CARS signal. The pump / Stokes light and probe light components transmitted into the second focusing lens FL2 are co-focused in the second gas cell, generating a CARS signal.

[0032] Furthermore, the receiving end mainly involves the extraction of CARS signals and the quantum enhanced receiving and detection module, including a first short-wave pass filter SPF1, a first beam collector BD1, a second short-wave pass filter SPF2, a second beam collector BD2, a variable optical attenuator VOA, a third optical delay stage, a quantum enhanced receiving and 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 for controlling the translation of the mirrors.

[0034] Furthermore, the quantum enhanced receiving detection module includes: a first long-wave pass filter LPF1, a second long-wave pass filter LPF2, a third long-wave pass filter LPF3, a third short-wave 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 out by the first short-wave pass filter SPF1 to remove the remaining pump / Stokes light and detection light, then attenuated by the variable optical attenuator VOA and transmitted to the first and third long-wave pass filters (LPF1, LPF3). The appropriate cutoff wavelengths of the first and third long-wave pass filters (LPF1, LPF3) are determined based on the Raman resonance frequency of the target gas. Furthermore, the target gas CARS signal is reflected by the third long-wave pass filter LPF3 and transmitted to the third beam splitter BS3.

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

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

[0038] The CARS signals reflected by the third long-wave pass filter LPF3 and transmitted by the third short-wave pass filter SPF3 are transmitted to the third beam splitter BS3 together and undergo interference and quantum shift operations. The quantum-shifted signals are detected by the single-photon detector PD.

[0039] The embodiment of the present invention further provides a method for realizing femtosecond / picosecond CARS gas detection based on quantum enhanced reception, which relies on the above-mentioned device for realizing femtosecond / picosecond CARS gas detection based on quantum enhanced reception, and is specifically as follows:

[0040] The light emitted by 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 by 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 the second beam splitter.

[0041] The first transmitted component of the pump / Stokes light is reflected by the first reflector M1 and then reflected by the first short-wavelength pass dichroic mirror SPDC1; the first transmitted component of the detection light is transmitted through the first short-wavelength pass dichroic mirror SPDC1 and coincides collinearly with the pump / Stokes light reflected by the first short-wavelength pass dichroic mirror SPDC1, and both are focused on the first gas pool by the first focusing lens FL1; by adjusting the first optical delay stage, the two beams of light reaching the first gas pool overlap in time and need to satisfy the collinear phase matching condition in space, thereby realizing the excitation of the gas molecules in the first gas pool and generating the CARS signal of the corresponding gas; the CARS signal generated by this path will serve as the signal arm of the quantum enhanced receiving and detection module and is recorded as signal light.

[0042] The first gas pool contains 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 respectively recorded as the second transmitted component and the second reflected component; the second reflected component of the pump / Stokes light is further reflected by the first short-wave pass dichroic mirror SPDC1 and the second short-wave pass dichroic mirror SPDC2 in sequence and then transmitted to the second focusing lens FL2; the second transmitted component of the pump / Stokes light is reflected by the second reflector M2 and further reflected by the second short-wave pass dichroic mirror SPDC2 through the second optical delay stage, and then collected by the third light collector BD3.

[0044] Furthermore, the first reflected component of the detection light is reflected by the second reflector M2 and then transmitted through the second optical delay stage and then transmitted through the second short-wave pass dichroic mirror SPDC2, and coincides collinearly with the second reflected component of the pump / Stokes light after being reflected by the first and second short-wave pass dichroic mirrors (SPDC1, SPDC2). The two are jointly focused by the second focusing lens FL2 on the second gas pool, and under the condition of satisfying collinear phase matching, the gas molecules in the second gas pool are excited to generate a CARS signal; the CARS signal generated by this path will serve as the reference arm of the quantum enhanced receiving detection module and is recorded as reference light.

[0045] Gases of known composition are placed in the second gas pool, which include most gases of concern in application scenarios such as combustion and gasification, such as N2, O2, CO, CO2, CH4, H2, etc.

[0046] The coherent anti-Stokes Raman scattering signal generated by the first and second gas cells and the remaining pump / Stokes light and probe light are transmitted forward together, and are filtered out by the first and second short-wave pass filters (SPF1 and SPF2), respectively, to remove the remaining pump / Stokes light and probe light. Since the anti-Stokes light is blue-shifted relative to the probe light, that is, its wavelength is reduced, the coherent anti-Stokes light in the two optical paths can be transmitted by properly selecting the cutoff wavelengths of the first and second short-wave pass filters (SPF1 and SPF2), while the remaining pump / Stokes light and probe light are reflected and collected by the first and second beam dumps (BD1 and BD2), respectively.

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

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

[0049] The first longpass filter LPF1 and the second longpass filter LPF2 have the same cutoff wavelength, denoted as the first cutoff wavelength. The third longpass filter LPF3 and the third shortpass filter SPF3 have the same or similar cutoff wavelength, denoted as the second cutoff wavelength. These two cutoff wavelengths are used to selectively detect a target molecule. Weak signal light with a wavelength above the first cutoff wavelength but below the second cutoff wavelength is transmitted through the first longpass filter LPF1 and reflected by the third longpass filter LPF3. Strong reference light with a wavelength above the first cutoff wavelength but below the second cutoff wavelength is sequentially transmitted by the second longpass filter LPF2 and the third shortpass filter SPF3. The signal and reference light beams converge at the third beam splitter BS3 with a 99:1 ratio. 99% of the weak signal light is reflected, while 1% of the strong reference light is transmitted, forming a quantum-enhanced reception and detection module.

[0050] Assuming N2 is present in the first gas cell (and an N2 gas sample is placed in the second gas cell), N2 CARS signals are generated in both the signal and reference beams. The N2 CARS signal wavelength is above the first cutoff wavelength and below the second cutoff wavelength. The CARS signal light generated by the signal arm is attenuated and ultimately reflected by the third longpass filter LPF3; the strong CARS reference light generated by the reference arm is ultimately transmitted by the third shortpass filter SPF3. By controlling the second optical delay stage, the optical path lengths of the signal and reference beams reaching the third beam splitter BS3 are equal, meaning that they arrive at the same phase at BS3. Subsequently, the two beams mix 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 light into a vacuum state, at which point the single-photon detector does not respond. When N2 is absent from the first gas cell, i.e., the input is in a vacuum state, the single-photon detector responds after the shift operation. Therefore, by sending a series of pulsed lasers and counting the counts of the single-photon detector, it can be determined whether N2 exists in the first gas pool.

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

[0052] Due to Raman shift It can be expressed 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 light wavelength is 515 nm, the corresponding CARS signal spectra of CO2, CO, N2, and H2 have center wavelengths of 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 cutoff wavelength of the filter in the system.

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

[0057] After passing through the first optical delay stage, the probe light is split by the second beamsplitter BS2. 50% of the probe light passes through BS2 and merges with the 50% of the pump / Stokes light transmitted by BS1 at SPDC1. The two beams travel forward in a colinear fashion and are focused by the first focusing lens FL1 onto the first gas cell, generating a CARS signal. This signal is filtered by the first shortpass filter SPF1 to remove the remaining pump / Stokes and probe light. It is then attenuated by a variable optical attenuator and serves as the signal light for the subsequent quantum-enhanced receiver detection module. SPF1 has a cutoff wavelength of 485nm to ensure that CARS signals from CO2, CO, N2, CH4, and H2 pass through SPF1.

[0058] The remaining 50% of the probe light is reflected by BS2 and again by the second reflector M2. It then passes through the second optical delay stage and SPDC2. This beam merges with the pump / Stokes light reflected by BS2, SPDC1, and SPDC2, and propagates forward in a colinear manner. It is then focused by the second focusing lens FL2 onto the second gas cell, generating a CARS signal. This signal, after filtering out the remaining pump / Stokes and probe light through the second shortpass filter SPF2, serves as the reference light for the subsequent quantum-enhanced receiver detection module. Similarly, SPF2 has a cutoff wavelength of 485 nm to ensure that the CARS signals of CO2, CO, N2, CH4, and H2 all pass through SPF2.

[0059] It's important to note that during the CARS signal generation phase, the first optical delay stage must be adjusted to synchronize the pump / Stokes light and probe light in the signal arm. The second optical delay stage is then adjusted to synchronize the probe light and pump / Stokes light in the reference beam path. Finally, the third optical delay stage is adjusted so that the Raman scattering signals from the signal and reference arms arrive at BS3 simultaneously, effectively interfering and achieving a shifting operation on the weak CARS signal light.

[0060] To determine whether the gas under test in the first gas cell contains N2, a gas chamber filled with N2 is placed in the second gas cell. Since the peak of the N2 CARS signal occurs at 459.8nm, the first longpass filter LPF1 and the second longpass filter LPF2 are selected with a cutoff wavelength of 458nm. Furthermore, the third longpass filter LPF3 and the third shortpass filter SPF3 are selected with a cutoff wavelength of 462nm. At this point, the CARS signal in the signal and reference arms, with a wavelength range between 458-462nm, can be transmitted to the third beam splitter BS3. If the CARS signal of the gas under test in the first gas cell contains N2, it is shifted to a vacuum state after a reference light shift operation, and the single-photon detector does not respond. If the gas under test in the first gas cell does not contain N2, i.e., the input is in a vacuum state, the single-photon detector responds after the shift operation. The single-photon detector counts are counted by sending a series of laser pulses.

[0061] Similarly, a gas chamber filled with CO is placed in the second gas pool. Since the CARS signal peak of CO appears at 463.8nm at this time, LPF1 and LPF2 with cutoff wavelengths of 462nm and LPF3 and SPF3 with cutoff wavelengths of 465nm 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 the single-photon detector. Within the same detection time as the previous N2, the counts of the single-photon detector are counted. The above operation is repeated for other CO2, CH4, and H2 gases. Finally, by comparing and analyzing the counts of the single-photon detector under different gas conditions placed in the second gas pool, the components and concentrations of gases such as CO2, CO, N2, CH4, and H2 in the first gas pool can be measured and analyzed.

[0062] Due to the ultra-broadband 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 cavity filled with different gases in the second gas pool, there is no need to replace the light source or adjust the optical path structure.

[0063] Although the preferred embodiments of the present application have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present application.

[0064] Obviously, those skilled in the art may make various changes and modifications to this application without departing from the spirit and scope of this application. Thus, if these modifications and variations of this application fall within the scope of the claims of this application and their equivalents, this application is intended to include these 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-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, which are arranged in sequence; The second optical path includes a detection light source, a first optical delay stage, a second beam splitter, a second reflector, 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, which are arranged in sequence; Part of the pump / Stokes light split by the first beam splitter is split again by the second beam splitter, 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%.

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

3. The femtosecond / picosecond CARS gas detection system based on quantum enhanced reception according to claim 1 is characterized in that: 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 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 is characterized in that: The pump / Stokes light is a femtosecond light source with a pulse width of <10 fs; the detection 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 is characterized in that: The first gas pool is filled with the gas to be tested, and the second gas pool is provided with five gas chambers which are filled with CO2, CO, N2, CH4 and H2 respectively.

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

50.

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

8. The femtosecond / picosecond CARS gas detection system based on quantum enhanced reception according to claim 1 is characterized in that: The cutoff wavelengths of the first long-wave pass filter and the second long-wave pass filter are the same; The cutoff wavelengths of the third long-wave pass filter and the third short-wave pass filter are the same.

9. The femtosecond / picosecond CARS gas detection system based on quantum enhanced reception according to claim 1, characterized in that: The beam splitting ratio of the third beam splitter is 99:

1.

10. A method for gas detection using the detection system according to any one of claims 1 to 9, characterized in that: The method includes: if it is necessary to determine whether the gas to be tested in the first gas pool contains a certain gas component, the gas is filled into the second gas pool. When the CARS signal of the gas to be tested in the first gas pool is detected to contain the gas component, the single-photon detector does not respond; when the CARS signal of the gas to be tested in the first gas pool is detected to not contain the gas component, the single-photon detector responds.

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