A high-precision multi-dimensional optical path collimation system based on CRDS

Abstract

This invention discloses a high-precision multi-dimensional optical path self-collimation system based on CRDS, relating to the field of spectral measurement technology. It includes a laser source, a semi-transparent mirror, a multi-dimensional optical path adjustment component, a ring-down cavity, a spot analyzer, and a control unit. The laser source comprises a measurement laser and a collimating laser, which are combined into a coaxial beam by the semi-transparent mirror. The multi-dimensional optical path adjustment component achieves horizontal and vertical position and angle adjustment of the beam through multiple sets of mirrors and a displacement driving structure. The ring-down cavity is equipped with high-reflectivity mirrors, bellows, and piezoelectric actuators at both ends, enabling precise adjustment of the high-reflectivity mirror's attitude. The spot analyzer acquires the position of the emitted spot and feeds it back to the control unit. The control unit drives each actuator to complete automatic optical path collimation through two levels of coarse and fine adjustment logic. This invention effectively improves the coupling efficiency, detection sensitivity, and environmental adaptability of the CRDS system, making it suitable for trace gas detection in complex scenarios such as industrial sites and environmental monitoring.

Description

Technical Field

[0001] This invention relates to the field of spectral measurement technology, and more particularly to an optical collimation control device for a cavity ring-down spectroscopy (CRDS) system, specifically a high-precision multidimensional optical path self-collimation system based on CRDS with adaptive adjustment capability. Background Technology

[0002] Cavity ring-down spectroscopy (CRDS) is an ultra-sensitive trace gas detection technique. It utilizes a high-reflectivity optical cavity to allow a laser to make multiple round trips within the cavity, accumulating and amplifying weak absorption signals. It is widely used in environmental monitoring, gas diagnostics for power equipment, atmospheric science, and industrial process monitoring. The detection sensitivity of a CRDS system essentially depends on the equivalent optical path length of the ring-down cavity, which is related to the reflectivity of the cavity mirrors and the fundamental mode (TEM) within the cavity. 00 The coupling efficiency is directly related. Only when the spatial distribution and wavefront curvature of the incident laser are strictly matched with the stable intrinsic modes of the optical cavity can a high-order transverse mode suppression ratio (CRDS) ring-down signal be effectively excited. Angular deviations or transverse displacements between the beam and the cavity axis directly introduce high-order mode coupling or external leakage, leading to multi-exponential decay or signal-to-noise ratio deterioration in the ring-down signal, thus significantly reducing measurement accuracy and long-term repeatability. Therefore, collimation is not only a matter of coupling efficiency but also a core prerequisite for the accuracy of CRDS quantitative analysis.

[0003] Chinese patent CN110196742A, entitled "A Trace Gas Detection System Based on CRDS," discloses a CRDS system combining a high-reflectivity cavity structure and a high-stability laser, capable of detecting trace gases such as SO2 and HF. This solution focuses on optimizing the cavity structure and detection performance, ensuring collimation accuracy solely through a high-precision mirror mounting structure. It does not address automatic optical path collimation or dynamic correction of coupling states; optical path collimation relies entirely on manual adjustment and mechanical fixation.

[0004] The 2017 paper by Zhang et al., "Real-Time Cavity Ring-Down Spectroscopy Sensor with Laser Beam Alignment Control," proposed a collimation scheme that incorporates real-time spot position monitoring using a photoelectric detection array and fine-tunes the laser incident angle using a mechanical platform. By optimizing adjustment parameters through laser power feedback, the system stability was improved to some extent. However, this scheme relies on manual initial calibration, has a long feedback control delay, struggles to cope with rapid disturbances in dynamic environments, and does not comprehensively consider the effects of multiple factors such as temperature and vibration, resulting in insufficient automation and robustness.

[0005] In general, current CRDS-related technologies and products generally suffer from the following shortcomings:

[0006] Low level of automation and high dependence on manual adjustment: Most systems rely on high-precision mechanical fixation during assembly and experience-based manual adjustment to achieve collimation. In long-term operation, they cannot automatically correct optical path deviations caused by thermal drift, mechanical loosening, mirror aging, etc., resulting in high maintenance costs and inability to adapt to complex on-site environments.

[0007] Insufficient dynamic feedback capability: It lacks real-time collimation status perception and closed-loop correction mechanism. When the optical path deviates during operation, it cannot be detected and corrected in time, which can easily lead to signal instability and data distortion.

[0008] Insufficient adjustment accuracy and response speed: The control resolution of the existing feedback collimation system is difficult to meet the collimation requirements of the nanoradian level of the CRDS cavity with high reflectivity (R>99.99%), and the adjustment mechanism has a slow response speed and cannot quickly suppress the influence of disturbances.

[0009] Lack of multi-dimensional adjustment capability: Conventional optical path adjustment mechanisms can only achieve single-dimensional position or angle adjustment, making it difficult to simultaneously complete horizontal and vertical multi-dimensional optical path correction, thus limiting collimation efficiency and accuracy.

[0010] Low integration level: The optical path collimation module and optical cavity structure are mostly designed separately, resulting in poor versatility and integrability, which restricts the miniaturization, portability and automation of CRDS system. Summary of the Invention

[0011] To address the shortcomings of existing technologies, the present invention aims to provide a high-precision multi-dimensional optical path self-collimation system based on CRDS, which realizes fully automatic real-time collimation and correction of laser and optical cavity, has horizontal and vertical multi-dimensional adjustment capabilities, and ensures nanoradius-level collimation accuracy through two-level adjustment logic, effectively improving the coupling efficiency, detection sensitivity and environmental adaptability of the CRDS system.

[0012] To achieve the above objectives, the present invention provides the following technical solution:

[0013] A high-precision multi-dimensional optical path self-collimation system based on CRDS includes a laser source and a ring-down cavity, as well as a semi-transparent and semi-reflective mirror, a multi-dimensional optical path adjustment component, a spot analyzer, and a control unit.

[0014] The laser source includes a measuring laser and a collimating laser. The measuring laser is used to output a measuring laser, and the collimating laser is used to output a collimating laser. The semi-transparent and semi-reflective mirror is disposed in the optical path where the measuring laser and the collimating laser intersect, and the two laser beams are combined into a coaxial beam through the semi-transparent and semi-reflective mirror.

[0015] The multidimensional optical path adjustment component is disposed between the output optical path of the coaxial beam and the incident optical path of the ring-down cavity, and includes multiple mirrors and a displacement and angle driving component; the displacement and angle driving component is connected to the corresponding mirror for driving the corresponding mirror to move, adjusting the position and angle of the incident coaxial beam in the horizontal and vertical dimensions, and outputting the adjusted beam to the ring-down cavity.

[0016] The two ends of the ring-down cavity are respectively equipped with a high-reflection mirror, a bellows, and a piezoelectric actuator. The high-reflection mirrors at both ends are arranged opposite each other to form a ring-down resonant cavity. The bellows is sealed between the cavity end and the mounting base of the high-reflection mirror to achieve a flexible sealed connection between the cavity and the corresponding high-reflection mirror. The piezoelectric actuator is driven by the corresponding high-reflection mirror and is used to adjust the position and orientation of the corresponding high-reflection mirror. The spot analyzer is set in the output light path of the ring-down cavity.

[0017] The control unit is electrically connected to the multidimensional optical path adjustment component, the piezoelectric actuator, and the light spot analyzer, respectively.

[0018] Furthermore, the measuring laser is incident on the semi-transparent mirror along the main optical axis of the system and transmitted, the collimated laser is incident on the semi-transparent mirror along a direction perpendicular to the main optical axis of the system and reflected, and the coaxial beam after beam combining is emitted along the main optical axis of the system.

[0019] Furthermore, the multidimensional optical path adjustment assembly includes a first reflector, a second reflector, a third reflector, a fourth reflector, a first linear displacement stage, and a second linear rotary displacement stage;

[0020] The first reflector is positioned on the outgoing light path of the semi-transparent mirror; the second reflector is positioned on the reflected light path of the first reflector; the third reflector is fixedly mounted on the platform of the first linear displacement stage, located on the reflected light path of the second reflector; the translation direction of the first linear displacement stage is vertical; the fourth reflector is fixedly mounted on the platform of the second linear rotary displacement stage, located on the reflected light path of the third reflector; the second linear rotary displacement stage has a horizontal translational degree of freedom and a rotational degree of freedom about a vertical axis; the outgoing light path of the fourth reflector is aligned with the incident end of the ring-down cavity.

[0021] The first linear displacement stage and the second linear rotary displacement stage together constitute the displacement and angle driving component.

[0022] Furthermore, the mounting base for the high-reflectivity mirror is a multi-dimensional collimator, with the high-reflectivity mirrors at both ends respectively mounted on a multi-dimensional collimator. The multi-dimensional collimator is sealed to the corresponding end of the optical cavity via a bellows. The piezoelectric actuator is mounted on the bellows and is used to drive the high-reflectivity mirror on the corresponding side to complete the fine adjustment of position and angle. The multi-dimensional collimator is used to drive the high-reflectivity mirror on the corresponding side to complete the coarse adjustment of attitude angle. Both the piezoelectric actuator and the multi-dimensional collimator are electrically connected to the control unit.

[0023] Furthermore, the cavity of the ring-down optical cavity is a stainless steel vacuum tube structure.

[0024] Furthermore, the spot analyzer is fixedly mounted on a precision displacement stage; the moving path of the precision displacement stage covers the outgoing light path and the outer area of ​​the ring-down cavity, which is used to drive the spot analyzer to move into the outgoing light path of the ring-down cavity to collect the spot position during the spectral measurement gap, and move out of the light path after the collection is completed.

[0025] The spot analyzer uses a Gaussian fitting algorithm to calculate the spot center offset and transmits the offset data to the control unit.

[0026] Furthermore, the first linear displacement stage, the second linear rotary displacement stage, and the precision displacement stage have built-in grating ruler position feedback structures, and the repeatability of positioning accuracy is not less than 1μm.

[0027] Furthermore, apertures are provided on the optical path between the semi-transparent mirror and the multi-dimensional optical path adjustment component, and on the optical path between the multi-dimensional optical path adjustment component and the ring-down cavity. The apertures are used to constrain the spot size and improve the measurement stability of the system. Two matching lenses are also provided after the aperture between the multi-dimensional optical path adjustment component and the ring-down cavity.

[0028] Furthermore, the control unit has a built-in automatic collimation control program, which includes two levels of adjustment logic: coarse adjustment and fine adjustment. The output of the coarse adjustment logic corresponds to the drive input of the multi-dimensional optical path adjustment component and the multi-dimensional collimator, respectively, and the output of the fine adjustment logic corresponds to the drive input of the piezoelectric actuator.

[0029] Furthermore, all optical components of the system are mounted on the optical breadboard via optical brackets, and the entire system is encapsulated in a stainless steel casing.

[0030] This system uses the center offset of the emitted beam from the cavity as the core feedback basis. Through the combination of multi-dimensional adjustment of the incident light path and two-stage fine-tuning of the cavity mirror attitude, it achieves high-precision dynamic self-collimation and stable operation of the CRDS cavity. During the collimation process, the two beams output from the measurement laser and the collimating laser are coaxially combined through a semi-transparent and semi-reflective mirror, making the collimating light path and the measurement light path completely coaxial. This ensures that the collimation adjustment result can directly affect the detection light path, eliminating the collimation error caused by the optical path deviation. After the coaxial beam enters the multi-dimensional optical path adjustment component, the light path is redirected by the first and second reflecting mirrors. The first linear displacement stage drives the third reflecting mirror to translate vertically, realizing the vertical position correction of the beam. The second linear rotary displacement stage drives the fourth reflecting mirror to complete the horizontal translation and angular deflection, simultaneously realizing the horizontal position and angle correction of the beam. The two work together to complete a large-range coarse adjustment of the two-dimensional attitude of the incident beam, so that the beam is initially aligned with the incident axis of the ringing-out cavity. The multidimensional collimator and piezoelectric actuator on the decaying optical cavity side constitute a coarse and fine two-stage adjustment mechanism for the cavity mirror attitude. The multidimensional collimator, in conjunction with the incident light path adjustment, completes a wide range of coarse adjustments to the cavity mirror attitude, rapidly reducing collimation deviation. The piezoelectric actuator, relying on nanometer-level driving resolution, performs sub-micrometer and nanoradian-level fine corrections to the cavity mirror position and angle, further optimizing the cavity resonance matching state. The two-stage mechanism works together to balance adjustment range and adjustment accuracy. In the feedback loop, the spot analyzer, relying on a precision displacement stage, enters the outgoing light path during the measurement gap, calculates the precise offset of the spot center using a Gaussian fitting algorithm, and transmits it to the control unit. The control unit, based on the two-stage adjustment logic, calculates the offset into the driving quantity of the corresponding actuator, and outputs control signals to the multidimensional optical path adjustment component, the multidimensional collimator, and the piezoelectric actuator, respectively, driving each component to correct in conjunction until the spot center offset converges to the threshold range, forming a complete closed-loop feedback control link. Under normal testing conditions, the collimating laser is turned off, the spot analyzer is removed from the optical path, and the measuring laser is efficiently coupled into the ring-down cavity after collimation to form a stable resonance, ensuring the stability of the ring-down signal and the detection accuracy. The system periodically triggers collimation calibration during measurement intervals to dynamically correct optical path drift caused by environmental disturbances such as temperature drift and vibration, achieving interference-free coordinated operation of the measurement and collimation processes.

[0031] Compared with the prior art, the beneficial effects of the present invention are:

[0032] 1. Achieve fully automatic optical path collimation without manual intervention: The spot offset status is detected in real time by the spot analyzer, and the control unit drives the adjustment mechanism to automatically correct in a closed loop. It can correct optical path offset caused by temperature drift, vibration, mechanical loosening, etc. in real time, which greatly reduces maintenance costs and improves the long-term stability of the system.

[0033] 2. Possesses multi-dimensional optical path adjustment capability: Through the cooperation of multiple sets of reflectors and displacement stages, the position and angle of the beam in both horizontal and vertical dimensions can be adjusted simultaneously, breaking through the limitations of conventional single-dimensional adjustment and improving collimation efficiency and adaptability.

[0034] 3. Two-stage adjustment ensures ultra-high collimation accuracy: The system adopts a graded control logic of "coarse adjustment + fine adjustment". In the coarse adjustment stage, a large-range alignment is completed through the displacement stage and the multi-dimensional collimator. In the fine adjustment stage, nano-arc-level precision adjustment is achieved through the piezoelectric actuator. This can meet the extremely high collimation requirements of high-Q CRDS optical cavities and ensure the coupling efficiency and detection sensitivity of the optical cavity.

[0035] 4. Measurement and collimation do not interfere with each other: The spot analyzer is mounted on a movable precision displacement stage. It only enters the optical path to collect data during measurement intervals and moves out of the optical path during normal detection, without affecting the normal trace gas detection process of the CRDS system.

[0036] 5. High integration and environmental adaptability: All optical components are integrated into an optical breadboard and encapsulated in a stainless steel shell. The structure is compact and has strong anti-interference capabilities, making it easy to integrate into various portable and fixed CRDS detection equipment. It is suitable for complex scenarios such as industrial sites, environmental monitoring, and field exploration.

[0037] 6. Possesses complete spatial mode matching capability: By introducing an adjustable mode matching lens group after multi-dimensional geometric adjustment, the beam quality control is elevated from simple "position angle correction" to the level of "spatial mode adaptation". This makes the system not only suitable for ideal Gaussian beams, but also able to actively compensate for the beam waist drift of actual laser output beams. This significantly improves the mode coupling stability of the CRDS system after laser replacement or long-term operation, fundamentally ensuring the single exponential purity and concentration inversion accuracy of the ring-down signal. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the overall optical path structure of the self-collimation system described in this invention;

[0039] Figure 2 This is a schematic diagram of the overall optical path system structure of the self-collimation system described in this invention;

[0040] Figure 3 This is a schematic diagram illustrating the principle of two-way laser beam combining as described in this invention;

[0041] Figure 4 This is a schematic diagram illustrating the spot fitting analysis effect of the spot analyzer described in this invention;

[0042] Figure 5 This is a schematic diagram of the control unit signal flow of the self-collimation system described in this invention;

[0043] Figure 6This is a block diagram illustrating the principle of the cavity ring-down spectroscopy (CRDS) method described in this invention.

[0044] Figure 7 This is a schematic diagram of the control unit software analysis and control interface described in this invention. Detailed Implementation

[0045] The technical solutions of the present invention will now be described in detail with reference to the accompanying drawings.

[0046] like Figures 1-7 As shown, a high-precision multi-dimensional optical path self-collimation system based on CRDS includes a laser source and a ring-down cavity, as well as a semi-transparent and semi-reflective mirror, a multi-dimensional optical path adjustment component, a spot analyzer, and a control unit.

[0047] The laser source includes a measuring laser and a collimating laser. The measuring laser is used to output a measuring laser, and the collimating laser is used to output a collimating laser. The semi-transparent and semi-reflective mirror is disposed in the optical path where the measuring laser and the collimating laser intersect, and the two laser beams are combined into a coaxial beam through the semi-transparent and semi-reflective mirror.

[0048] The multidimensional optical path adjustment component is disposed between the output optical path of the coaxial beam and the incident optical path of the ring-down cavity, and includes multiple mirrors and a displacement and angle driving component; the displacement and angle driving component is connected to the corresponding mirror for driving the corresponding mirror to move, adjusting the position and angle of the incident coaxial beam in the horizontal and vertical dimensions, and outputting the adjusted beam to the ring-down cavity.

[0049] The two ends of the ring-down cavity are respectively equipped with a high-reflection mirror, a bellows, and a piezoelectric actuator. The high-reflection mirrors at both ends are arranged opposite each other to form a ring-down resonant cavity. The bellows is sealed between the cavity end and the mounting base of the high-reflection mirror to achieve a flexible sealed connection between the cavity and the corresponding high-reflection mirror. The piezoelectric actuator is driven by the corresponding high-reflection mirror and is used to adjust the position and orientation of the corresponding high-reflection mirror. The spot analyzer is set in the output light path of the ring-down cavity.

[0050] The control unit is electrically connected to the multidimensional optical path adjustment component, the piezoelectric actuator, and the light spot analyzer, respectively.

[0051] Furthermore, the measuring laser is incident on the semi-transparent mirror along the main optical axis of the system and transmitted, the collimated laser is incident on the semi-transparent mirror along a direction perpendicular to the main optical axis of the system and reflected, and the coaxial beam after beam combining is emitted along the main optical axis of the system.

[0052] Furthermore, the multidimensional optical path adjustment assembly includes a first reflector, a second reflector, a third reflector, a fourth reflector, a first linear displacement stage, and a second linear rotary displacement stage;

[0053] The first reflector is positioned on the outgoing light path of the semi-transparent mirror; the second reflector is positioned on the reflected light path of the first reflector; the third reflector is fixedly mounted on the platform of the first linear displacement stage, located on the reflected light path of the second reflector; the translation direction of the first linear displacement stage is vertical; the fourth reflector is fixedly mounted on the platform of the second linear rotary displacement stage, located on the reflected light path of the third reflector; the second linear rotary displacement stage has a horizontal translational degree of freedom and a rotational degree of freedom about a vertical axis; the outgoing light path of the fourth reflector is aligned with the incident end of the ring-down cavity.

[0054] The first linear displacement stage and the second linear rotary displacement stage together constitute the displacement and angle driving component.

[0055] Furthermore, the mounting base for the high-reflectivity mirror is a multi-dimensional collimator, with the high-reflectivity mirrors at both ends respectively mounted on a multi-dimensional collimator. The multi-dimensional collimator is sealed to the corresponding end of the optical cavity via a bellows. The piezoelectric actuator is mounted on the bellows and is used to drive the high-reflectivity mirror on the corresponding side to complete the fine adjustment of position and angle. The multi-dimensional collimator is used to drive the high-reflectivity mirror on the corresponding side to complete the coarse adjustment of attitude angle. Both the piezoelectric actuator and the multi-dimensional collimator are electrically connected to the control unit.

[0056] Furthermore, the cavity of the ring-down optical cavity is a stainless steel vacuum tube structure.

[0057] Furthermore, the spot analyzer is fixedly mounted on a precision displacement stage; the moving path of the precision displacement stage covers the outgoing light path and the outer area of ​​the ring-down cavity, which is used to drive the spot analyzer to move into the outgoing light path of the ring-down cavity to collect the spot position during the spectral measurement gap, and move out of the light path after the collection is completed.

[0058] The spot analyzer uses a Gaussian fitting algorithm to calculate the spot center offset and transmits the offset data to the control unit.

[0059] Furthermore, the first linear displacement stage, the second linear rotary displacement stage, and the precision displacement stage have built-in grating ruler position feedback structures, and the repeatability of positioning accuracy is not less than 1μm.

[0060] Furthermore, apertures are provided on the optical path between the semi-transparent mirror and the multi-dimensional optical path adjustment component, and on the optical path between the multi-dimensional optical path adjustment component and the ring-down cavity. The apertures are used to constrain the spot size and improve the measurement stability of the system. Two matching lenses are also provided after the aperture between the multi-dimensional optical path adjustment component and the ring-down cavity.

[0061] Furthermore, the control unit has a built-in automatic collimation control program, which includes two levels of adjustment logic: coarse adjustment and fine adjustment. The output of the coarse adjustment logic corresponds to the drive input of the multi-dimensional optical path adjustment component and the multi-dimensional collimator, respectively, and the output of the fine adjustment logic corresponds to the drive input of the piezoelectric actuator.

[0062] Furthermore, all optical components of the system are mounted on the optical breadboard via optical brackets, and the entire system is encapsulated in a stainless steel casing.

[0063] The high-precision multi-dimensional optical path self-collimation system based on CRDS described in this invention has all optical components and adjustment actuators mounted on an optical breadboard via optical mounting brackets. The entire system is encapsulated in a stainless steel shell, forming an integrated module with good vibration resistance and environmental adaptability. It is suitable for various complex application scenarios such as industrial sites, environmental monitoring, and field exploration.

[0064] The system is arranged along the main optical axis as follows: laser source, beam combining unit, multi-dimensional optical path adjustment component, mode matching lens group, ring-down cavity and spot acquisition unit, forming a complete collimation and detection optical path link. It can simultaneously realize laser multi-dimensional attitude adjustment, cavity resonant coupling and collimation state closed-loop feedback functions. The overall optical path structure of the system is as follows: Figure 1 As shown, the complete optical path system layout structure is as follows: Figure 2 As shown.

[0065] The system is equipped with two laser sources: a measurement laser and a collimating laser. The measurement laser outputs the measurement laser for trace gas detection, while the collimating laser outputs the collimating laser for optical path calibration. The two lasers are coaxially combined using a semi-transparent mirror. The measurement laser is incident on the semi-transparent mirror along the system's principal optical axis and passes through it. The collimating laser is incident on the semi-transparent mirror along a direction perpendicular to the principal optical axis and is reflected. The two beams then overlap after passing through the semi-transparent mirror and continue propagating along the principal optical axis. The principle of beam combining the two lasers is as follows: Figure 3 As shown, an aperture is provided on the exit side of the semi-transparent mirror to constrain the beam size, filter out stray light, optimize beam quality, and improve system stability.

[0066] After being combined, the coaxial beam is constrained by an aperture and then enters a multi-dimensional optical path adjustment component. This component, through the cooperation of multiple sets of reflectors and a displacement driving platform, can achieve joint adjustment of the beam's position and angle in both the horizontal and vertical dimensions. Within the component, a first, second, third, and fourth reflector are sequentially arranged along the optical path. The beam first enters the first reflector, and after reflection, its transmission direction is changed before entering the second reflector. The second reflector then redirects the beam before it enters the third reflector. The third reflector is fixedly mounted on the surface of a first linear displacement stage, whose translation direction is vertical. By driving the third reflector to translate along the vertical direction, the vertical exit position of the beam can be changed, thus achieving vertical position adjustment of the beam.

[0067] The beam reflected by the third mirror is incident on the fourth mirror, which is fixedly mounted on the platform of the second linear rotary displacement stage. This stage has both horizontal translational freedom and rotational freedom about the vertical axis. Horizontal translational motion changes the horizontal exit position of the beam, while rotational motion about the vertical axis changes the horizontal exit angle. These two actions work together to achieve comprehensive adjustment of the beam's horizontal position and angle. After multi-dimensional adjustment, the beam passes through an aperture to constrain stray light before entering the mode-matching lens group and then the incident end of the ring-down cavity. The mode-matching lens group, along the optical path, includes a first matching lens and a second matching lens, each mounted on a corresponding miniature linear displacement drive mechanism. The control unit, based on the cavity's theoretical fundamental mode parameters (beam waist radius ω0 and beam waist position z0), combined with the actual M² factor and measured beam waist value of the current incident beam, continuously adjusts the beam waist position and size by driving the relative distance between the two lenses. During the fine-tuning stage of collimation adjustment, in addition to adjusting the cavity mirror attitude with the piezoelectric actuator, the control unit simultaneously performs micro-scanning of the lens spacing with the goal of minimizing the single exponential fitting residual of the decay signal. This ensures that the incident beam and the fundamental mode of the optical cavity achieve a mode matching state with a spatial overlap integral greater than 99.5%, thereby effectively suppressing the excitation of higher-order modes.

[0068] Both the first linear displacement stage and the second linear rotary displacement stage have built-in grating ruler position feedback structures, with a repeatability of not less than 1μm, which can ensure high precision and high repeatability of displacement adjustment and ensure that the optical path adjustment process is accurate and controllable.

[0069] The ring-down resonant cavity is constructed using a stainless steel vacuum tube, providing excellent airtightness and structural strength, and is suitable for gas detection under vacuum or positive pressure conditions. High-reflectivity mirrors, bellows, multi-dimensional collimators, and piezoelectric actuators are respectively installed at both ends of the cavity. The high-reflectivity mirrors at both ends are aligned and coaxially arranged to form the ring-down resonant cavity.

[0070] The high-reflectivity mirror is mounted on a multi-dimensional collimator, which is sealed to the end of the cavity via a bellows. The bellows ensures the overall airtightness of the cavity while providing flexible displacement margins to accommodate the attitude adjustment movements of the high-reflectivity mirror. The multi-dimensional collimator can drive the high-reflectivity mirror on the corresponding side to complete a wide range of attitude angle adjustments, suitable for initial system installation collimation and coarse adjustments during significant optical path offsets. A piezoelectric actuator is mounted at the corresponding position of the bellows and connected to the high-reflectivity mirror drive, enabling the high-reflectivity mirror to produce micron-level positional shifts and nanoradian-level angular deflections, achieving high-precision fine adjustment of the high-reflectivity mirror's attitude.

[0071] A spot analyzer is installed on the output side of the ring-down cavity to collect the position information of the emitted light spot. The spot analyzer is fixedly mounted on a precision displacement stage, whose movement direction is perpendicular to the main optical axis of the cavity, and its movement range covers the main optical axis region and the outer region of the optical path. During normal spectral measurements, the precision displacement stage moves the spot analyzer out of the main optical path to avoid obstructing the measurement beam and interfering with the detection process. During the measurement interval for optical path collimation calibration and adjustment, the precision displacement stage moves the spot analyzer into the main optical path to collect a complete image of the emitted light spot. The precision displacement stage also incorporates a grating ruler position feedback structure, with a repeatability accuracy of no less than 1μm, ensuring accurate and repeatable entry and exit positions.

[0072] The spot analyzer incorporates a Gaussian fitting algorithm to perform Gaussian fitting calculations on the acquired spot images. This allows for precise determination of the spot center's coordinates and its offset relative to the target position. The analysis results of the spot fitting are as follows: Figure 4 As shown, the calculated offset data is transmitted to the control unit in real time as feedback for closed-loop adjustment.

[0073] The control unit, as the core of the system, is electrically connected to each displacement stage, the multidimensional collimator and piezoelectric actuator of the ring-down cavity, the spot analyzer, and the precision displacement stage within the multidimensional optical path adjustment assembly. This achieves a complete closed loop of signal acquisition, logic operation, and drive control. The signal transmission path between the control unit and each component is as follows: Figure 5 As shown.

[0074] The control unit has a built-in automatic collimation control program, employing a two-stage adjustment logic of coarse and fine adjustment. The overall collimation feedback control principle is as follows: Figure 6 As shown. The accompanying software analysis and control interface can display the spot status, adjust parameters, and system operating mode in real time, supporting parameter configuration and operating status monitoring. The specific software interface format is as follows. Figure 7 As shown.

[0075] The collimation adjustment process of the system is divided into three stages: coarse adjustment, fine adjustment, and routine verification. In scenarios such as initial system startup, significant optical path offset, or first calibration, the system starts the coarse adjustment mode. The control unit outputs drive signals to the displacement stages of the multi-dimensional optical path adjustment component and the multi-dimensional collimators at both ends of the ringing-down cavity, respectively adjusting the position angle of the incident beam and the approximate attitude of the high-reflection mirror. Combined with the real-time feedback data from the spot analyzer, the center of the spot is adjusted to the target area, completing the initial alignment.

[0076] After coarse adjustment, the system automatically switches to fine adjustment mode. The control unit outputs a high-precision drive signal to the piezoelectric actuators at both ends to finely adjust the position and deflection angle of the high-reflection mirror, gradually reducing the offset of the center of the light spot. At the same time, it can combine the intensity and decay time of the cavity decay signal for auxiliary judgment until the cavity reaches the optimal resonant coupling state, thus completing high-precision collimation.

[0077] During the daily operation of the system, the control unit will periodically initiate the collimation verification process during the measurement interval, control the precision displacement stage to drive the spot analyzer to enter the optical path and detect the current spot offset; if the offset exceeds the preset threshold, the fine adjustment process will be automatically initiated for correction; if the offset is within the threshold range, the spot analyzer will be moved out of the optical path and normal measurement will be restored, thereby ensuring that the optical path always maintains a good collimation state during long-term operation of the system.

[0078] After optical path collimation is completed, the system enters normal detection mode. The collimating laser is turned off, and the measuring laser outputs the measuring laser. The beam is coupled into the ring-down cavity through the beam combining optical path and the multi-dimensional optical path adjustment component. It oscillates back and forth between two highly reflective mirrors multiple times. The gas to be measured in the cavity absorbs the laser, causing the light intensity to gradually decrease. The attenuated light signal emitted from the cavity is received by the back-end photoelectric detection module. The ring-down time is obtained by exponential fitting of the signal. Combined with the reference ring-down time when there is no absorption, the concentration of the gas to be measured in the cavity can be calculated, thus completing the trace gas detection.

[0079] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings. These embodiments are merely descriptions of preferred embodiments and are not intended to limit the scope or concept of the invention. The specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. Such combinations, as long as they do not violate the spirit of the present invention, should also be considered as part of this disclosure. To avoid unnecessary repetition, the present invention will not further describe the various possible combinations.

[0080] This invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this invention and without departing from the design idea of ​​this invention, all modifications and improvements made by those skilled in the art to the technical solutions of this invention should fall within the protection scope of this invention. The technical content for which protection is sought in this invention has been fully described in the claims.

Claims

1. A high-precision multi-dimensional optical path self-collimation system based on CRDS, comprising a laser source and a ring-down cavity, characterized in that, It also includes a semi-transparent and semi-reflective mirror, a multi-dimensional optical path adjustment component, a spot analyzer, and a control unit; The laser source includes a measuring laser and a collimating laser. The measuring laser is used to output a measuring laser, and the collimating laser is used to output a collimating laser. The semi-transparent and semi-reflective mirror is disposed in the optical path where the measuring laser and the collimating laser intersect, and the two laser beams are combined into a coaxial beam through the semi-transparent and semi-reflective mirror. The multidimensional optical path adjustment component is disposed between the output optical path of the coaxial beam and the incident optical path of the ring-down cavity, and includes multiple mirrors and a displacement and angle driving component; the displacement and angle driving component is connected to the corresponding mirror for driving the corresponding mirror to move, adjusting the position and angle of the incident coaxial beam in the horizontal and vertical dimensions, and outputting the adjusted beam to the ring-down cavity. The two ends of the ring-down cavity are respectively equipped with a high-reflection mirror, a bellows, and a piezoelectric actuator. The high-reflection mirrors at both ends are arranged opposite each other to form a ring-down resonant cavity. The bellows is sealed between the cavity end and the mounting base of the high-reflection mirror to achieve a flexible sealed connection between the cavity and the corresponding high-reflection mirror. The piezoelectric actuator is driven by the corresponding high-reflection mirror and is used to adjust the position and orientation of the corresponding high-reflection mirror. The spot analyzer is set in the output light path of the ring-down cavity. The control unit is electrically connected to the multidimensional optical path adjustment component, the piezoelectric actuator, and the light spot analyzer, respectively.

2. The high-precision multi-dimensional optical path self-collimation system based on CRDS according to claim 1, characterized in that, The measuring laser is incident on the semi-transparent mirror along the main optical axis of the system and is transmitted. The collimated laser is incident on the semi-transparent mirror along a direction perpendicular to the main optical axis of the system and is reflected. The coaxial beam after beam combining is emitted along the main optical axis of the system.

3. A high-precision multi-dimensional optical path self-collimation system based on CRDS according to claim 1, characterized in that, The multidimensional optical path adjustment assembly includes a first reflector, a second reflector, a third reflector, a fourth reflector, a first linear displacement stage, and a second linear rotary displacement stage; The first reflector is positioned on the outgoing light path of the semi-transparent mirror; the second reflector is positioned on the reflected light path of the first reflector; the third reflector is fixedly mounted on the platform of the first linear displacement stage, located on the reflected light path of the second reflector; the translation direction of the first linear displacement stage is vertical; the fourth reflector is fixedly mounted on the platform of the second linear rotary displacement stage, located on the reflected light path of the third reflector; the second linear rotary displacement stage has a horizontal translational degree of freedom and a rotational degree of freedom about a vertical axis; the outgoing light path of the fourth reflector is aligned with the incident end of the ring-down cavity. The first linear displacement stage and the second linear rotary displacement stage together constitute the displacement and angle driving component.

4. A high-precision multi-dimensional optical path self-collimation system based on CRDS according to claim 1, characterized in that, The mounting base for the high-reflection mirror is a multi-dimensional collimator, with the high-reflection mirrors at both ends respectively mounted on a multi-dimensional collimator. The multi-dimensional collimator is sealed to the corresponding end of the optical cavity via a bellows. The piezoelectric actuator is mounted on the bellows and is used to drive the high-reflection mirror on the corresponding side to complete the fine adjustment of position and angle. The multi-dimensional collimator is used to drive the high-reflection mirror on the corresponding side to complete the coarse adjustment of attitude angle. Both the piezoelectric actuator and the multi-dimensional collimator are electrically connected to the control unit.

5. A high-precision multi-dimensional optical path self-collimation system based on CRDS according to claim 4, characterized in that, The cavity of the ring-down optical cavity is a stainless steel vacuum tube structure.

6. A high-precision multi-dimensional optical path self-collimation system based on CRDS according to claim 1, characterized in that, The spot analyzer is fixedly mounted on a precision displacement stage; the moving path of the precision displacement stage covers the outgoing light path and the outer area of ​​the ring-down cavity, and is used to drive the spot analyzer to move into the outgoing light path of the ring-down cavity to collect the spot position during the spectral measurement gap, and move out of the light path after the collection is completed. The spot analyzer uses a Gaussian fitting algorithm to calculate the spot center offset and transmits the offset data to the control unit.

7. A high-precision multi-dimensional optical path self-collimation system based on CRDS according to claim 3 or 6, characterized in that, The first linear displacement stage, the second linear rotary displacement stage, and the precision displacement stage have built-in grating ruler position feedback structures, and the repeatability positioning accuracy is not less than 1μm.

8. A high-precision multi-dimensional optical path self-collimation system based on CRDS according to claim 1, characterized in that, Apertures are provided on the optical path between the semi-transparent mirror and the multi-dimensional optical path adjustment component, and on the optical path between the multi-dimensional optical path adjustment component and the ring-down cavity. The apertures are used to constrain the spot size and improve the measurement stability of the system. Two matching lenses are also provided after the aperture between the multi-dimensional optical path adjustment component and the ring-down cavity.

9. A high-precision multi-dimensional optical path self-collimation system based on CRDS according to claim 1, characterized in that, The control unit has a built-in automatic collimation control program, which includes two levels of adjustment logic: coarse adjustment and fine adjustment. The output of the coarse adjustment logic corresponds to the drive input of the multi-dimensional optical path adjustment component and the multi-dimensional collimator, respectively, and the output of the fine adjustment logic corresponds to the drive input of the piezoelectric actuator.

10. A high-precision multi-dimensional optical path self-collimation system based on CRDS according to claim 1, characterized in that, All optical components of the system are mounted on an optical breadboard using optical mounting brackets, and the entire system is encapsulated in a stainless steel housing.

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