A device and method for measuring misalignment error of a ring cavity ring-down spectroscopy device

Abstract

The present invention relates to the field of cavity ring-down spectroscopy technology, and in particular to a device for measuring misalignment errors in a ring cavity ring-down spectroscopy device, comprising a laser light source, a collimated matching alignment optical path, a passive triangular resonant cavity, a focusing mirror, a detector, and a data acquisition, recording, and analysis mechanism. The passive triangular resonant cavity is also connected to a resonance establishment mechanism and a cavity length servo control mechanism. The present invention also provides a method for measuring misalignment errors in a ring cavity ring-down spectroscopy device, comprising: S1: ensuring that the ring cavity optical path satisfies the closed optical axis characteristic; S2: ensuring that the laser light source and the passive triangular resonant cavity meet preliminary alignment conditions; S3: ensuring that the passive triangular resonant cavity meets resonance conditions and establishes a threshold light intensity; S4: performing wavelength scanning after resonance is established; and S5: obtaining misalignment information. The present invention can solve the problem that existing cavity ring-down spectroscopy devices still have corresponding misalignment errors after resonance is established, which affects the size of the resonance peak and lacks corresponding information to guide alignment.

Description

Technical Field

[0001] The present invention relates to the technical field of cavity ring-down spectroscopy, and in particular to a device and method for measuring misalignment errors of a ring cavity ring-down spectroscopy device. Background Art

[0002] Cavity ring-down spectroscopy (CRM) offers the advantages of high speed (microseconds), portability (lightweight design allows it to fit into a backpack), high spectral resolution (several MHz), and high accuracy (up to ppbv). It can be used to measure the concentrations of various trace gases in both conventional and extreme environments. Applications for CRM include atmospheric surface environmental monitoring, biomedical diagnostics, deep-sea resource exploration, industrial process control, and combustion diagnostics.

[0003] The core optical resonator structure of existing cavity ring-down spectroscopy (CRS) devices often uses a straight cavity structure. While straight cavities offer advantages such as strong stability and easy adjustment, they also suffer from disadvantages such as an inability to effectively suppress optical feedback and the presence of etalon effects. CRS devices using triangular cavities effectively address these issues, but also come with challenges such as complex adjustment, low alignment accuracy, and poor stability. Therefore, effectively determining the adjustment errors present in triangular resonators is crucial.

[0004] Existing installation and adjustment schemes usually first require the alignment of the annular cavity, often using a tripod adjustment seat or other angle fine-tuning mechanisms, and performing fine-tuning based on a reference optical path or other auxiliary standard parts. During the fine-tuning process, in order to achieve alignment between the light source optical path and the optical path in the cavity, the adjustment process is random and accurate misalignment error information cannot be obtained. Therefore, if an installation and adjustment error occurs during use, it cannot be eliminated in real time and needs to be returned to the factory for reinstallation, which greatly affects the environmental applicability and maintainability of the instrument.

[0005] In the prior art, the following prior art discloses technical solutions for cavity ring-down spectroscopy measurement.

[0006] 1. Chinese patent publication number CN114235706A, titled "A Flexible Sealed Tuning Device for a Ring-Down Cavity," discloses a flexible sealed tuning device for a ring-down cavity. The device ensures high-precision, high-stability, high-sealing, and high-rigidity calibration during ring-down cavity tuning. However, it does not address a technical solution for obtaining offset errors in a triangular cavity ring-down spectroscopy device.

[0007] 2. Chinese patent publication number CN109580541A, titled "An Optical Heterodyne Cavity Ring-Down Spectroscopy Measurement Device and Method," discloses a cavity ring-down spectroscopy measurement device and method capable of improving measurement accuracy. However, it also fails to address a technical solution for obtaining offset errors in a triangular cavity ring-down spectroscopy device.

[0008] In summary, how to propose a device and method for obtaining misalignment errors in a triangular cavity ring-down spectroscopy device that can achieve planar, directional, and high-precision alignment is a problem that needs to be solved urgently. Summary of the Invention

[0009] To solve the above problems, the present invention provides a device and method for measuring the misalignment error of a ring cavity ring-down spectroscopy device. The device and method can solve the problems of existing cavity ring-down spectroscopy devices, such as the corresponding misalignment error still existing after resonance is established, affecting the size of the resonance peak, the randomness of high-precision adjustment, and the lack of corresponding information to guide alignment. The device can achieve planar, directional, and high-precision alignment.

[0010] To achieve the above-mentioned purpose, the present invention proposes the following technical solutions: a device for measuring the misalignment error of a ring cavity ring-down spectroscopy device, comprising a laser light source, a collimated matching alignment optical path, a passive triangular resonant cavity, a focusing mirror, a detector and a data acquisition, recording and analysis mechanism arranged in sequence from the incident direction of the light source to the exit direction of the light source; the laser light source comprises a light source part and a wavelength tuning part, for realizing the emission of the light source and scanning of the wavelength of the light source; the passive triangular resonant cavity is used to receive the energy of the light source to realize the establishment of a resonance peak, and the collimated matching alignment optical path is used to match the beam characteristics of the light source with the beam characteristics of the passive triangular resonant cavity; the detector is used to obtain the energy of the exit light of the passive triangular resonant cavity; the data acquisition, recording and analysis mechanism is used to obtain the tilt and axial translation errors between the optical axis of the light source and the optical axis in the passive triangular resonant cavity; the passive triangular resonant cavity is also connected to a resonance establishment mechanism and a cavity length servo control mechanism, the resonance establishment mechanism is used to scan the cavity length and make the passive triangular resonant cavity meet the resonance condition, and the cavity length servo control mechanism is used to realize cavity length adjustment.

[0011] Preferably, the passive triangular resonant cavity includes a first cavity mirror with a plane mirror structure, a first cavity mirror and a third cavity mirror with a curved structure, and the optical path between the first cavity mirror, the second cavity mirror and the third cavity mirror forms a closed optical axis loop of the triangular cavity; the resonance establishing mechanism includes a piezoelectric ceramic bonded to the third cavity mirror, and the cavity length servo control mechanism is connected to the piezoelectric ceramic, and the cavity length servo control mechanism controls the piezoelectric ceramic to achieve cavity length adjustment.

[0012] Preferably, the collimation matching alignment optical path includes a collimation lens group connected to the laser light source and an alignment lens group connected to the passive triangular resonant cavity, and a matching lens group and a beam splitter are provided between the collimation lens group and the alignment lens group along the optical path direction.

[0013] Preferably, the alignment lens group includes a first alignment lens group and a second alignment lens group arranged in parallel. After the first light beam at the spectroscope is incident on the alignment lens group, it is aligned twice by the first alignment lens group and the second alignment lens group and then emitted in parallel into the passive triangular resonant cavity.

[0014] Preferably, a reference light modulation mechanism is also connected between the spectrometer and the cavity length servo mechanism. The second light beam at the spectrometer is added with a frequency sideband through the reference light modulation mechanism and mixed with the light beam emitted from the passive triangular resonant cavity to achieve stable matching of the frequency in the cavity and the frequency of the light source.

[0015] Preferably, an optical amplifier is included between the alignment lens assembly and the passive triangular resonant cavity to enhance the energy of the transmitted light at the resonant frequency in the passive triangular resonant cavity.

[0016] Preferably, the passive triangular resonant cavity further includes an air inlet, an air outlet, a gas filter, a cavity temperature measurer, and a cavity pressure measurer.

[0017] A method for measuring the misalignment error of a ring cavity ring-down spectroscopy device, using the above-mentioned measurement device for testing, comprises the following steps:

[0018] S1: Make the ring cavity optical path meet the closed optical axis characteristics: by designing the cavity length, cavity angle and curvature of the third cavity mirror in the triangular cavity closed optical axis loop to meet the resonant cavity stability condition and closed optical axis condition;

[0019] S2: Make the laser light source and the passive triangular resonant cavity meet the preliminary alignment conditions: the light emitted by the laser light source passes through the center of the collimating lens group and the matching lens group in turn, the first light beam passing through the beam splitter and then through the alignment lens group into the center of the first cavity mirror in the passive triangular resonant cavity, and achieves preliminary alignment with the optical axis in the passive triangular resonant cavity.

[0020] S3: The passive triangular resonant cavity is made to meet the resonance condition and establish the threshold light intensity through the cavity length servo control mechanism;

[0021] S4: After the resonance is established, the light source realizes a wavelength scan in a free spectrum range, and the transmitted light intensity information in a wavelength range is recorded by the data acquisition, recording and analysis mechanism;

[0022] S5: Obtain misalignment information through the transmitted light intensity data.

[0023] Preferably, the light emitted by the light source passes through the matching lens group and the alignment lens group and enters the passive triangular resonant cavity. In step S3, when the passive triangular resonant cavity does not meet the resonance condition, the light energy received by the detector after passing through the focusing lens is weak, and the detector does not respond; at this time, the cavity length servo control mechanism controls the piezoelectric ceramic and realizes cavity length adjustment; when the passive triangular resonant cavity meets the resonance condition, the light energy in the passive triangular resonant cavity accumulates rapidly, and the detector realizes the establishment of the output light intensity.

[0024] Preferably, in S5, the peak value when the resonance is first reached is taken as the zero point, and two sub-peaks between the peak value and the next peak value are selected for analysis; the two sub-peaks are the TEM01 mode and the TEM10 mode, and the resonant frequencies of the TEM01 mode and the TEM10 mode are calculated by formula (1) and formula (2), respectively:

[0025]

[0026]

[0027] Wherein, FSR is the free spectral range of the passive triangular resonant cavity, L is the cavity length of the passive triangular resonant cavity, and R is the curvature radius of the third cavity mirror.

[0028] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0029] 1. The present invention can solve the randomness of conventional alignment methods of the cavity ring-down spectroscopy device after the resonance is established, avoid the corresponding misalignment error that affects the size of the resonance peak, and realize the misalignment error acquisition of the plane, direction, and high-precision alignment, greatly improving the installation and adjustment rate.

[0030] 2. The optical path between the first cavity mirror, the second cavity mirror and the third cavity mirror in the passive triangular resonant cavity of the present invention forms a triangular cavity closed optical axis loop, which can compensate for the influence of straight cavity light feedback and achieve optical axis alignment.

[0031] 3. The cavity length servo control mechanism in the present invention can control the piezoelectric ceramic bonded to the third cavity mirror to achieve cavity length adjustment. When the resonance condition is met during the cavity length scanning process, the light energy in the cavity accumulates rapidly, and the detector can establish the output light intensity. At the same time, the reference light modulation mechanism can be used to add frequency sidebands to the second light beam, and mix it with the light beam emitted from the passive triangular resonant cavity to achieve long-term stable matching of the cavity frequency and the light source frequency, thereby overcoming the influence of light source fluctuations. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a structural schematic diagram of a detuning error measuring device of a ring cavity ring-down spectroscopy device provided by an embodiment of the present invention.

[0033] Figure 2 Schematic diagram of the structure of the passive triangular resonant cavity provided by an embodiment of the present invention.

[0034] Figure 3 Schematic diagram of the structure of the matching lens assembly provided by an embodiment of the present invention.

[0035] Figure 4 1 is a schematic flow chart of the steps of a method for measuring the misalignment error of a ring cavity ring-down spectroscopy device provided in an embodiment of the present invention.

[0036] Reference numerals:

[0037] Laser light source 1, collimating lens group 2, matching lens group 3, spectrometer group 4, alignment lens group 5, passive triangular resonant cavity 6, first cavity mirror 7, second cavity mirror 8, third cavity mirror 9, focusing lens 10, detector 11, data acquisition, recording and analysis mechanism 12, air inlet 13, gas filter 14, air outlet 15, cavity temperature measurer 16, cavity pressure measurer 17, piezoelectric ceramic 18, cavity length servo control mechanism 19, reference light modulation mechanism 20, main control mechanism 21, optical amplifier 22, conventional Galilean telescope group 301, cylindrical lens 302, first alignment lens group 501, second alignment lens group 502. DETAILED DESCRIPTION

[0038] In the following, reference will be made to the Figure 1-4 Describe the embodiment of the present invention. In the following description, the same modules are represented by the same reference numerals. In the case of the same reference numerals, their names and functions are also the same. Therefore, their detailed description will not be repeated.

[0039] A device for measuring misalignment errors of a ring cavity ring-down spectroscopy device includes a main control mechanism 21, such as Figure 1 As shown, it also includes a laser light source 1, a collimation matching alignment optical path, a passive triangular resonant cavity 6, a focusing mirror 10, a detector 11 and a data acquisition, recording and analysis mechanism 12, which are arranged in sequence from the incident direction of the light source to the emitting direction of the light source. The passive triangular resonant cavity 6 is also connected to a resonance establishment mechanism and a cavity length servo control mechanism 19.

[0040] The laser light source 1 includes a light source part and a wavelength tuning part, which are used to generate a laser beam, realize the emission of the light source and scan the wavelength of the light source.

[0041] The collimation matching alignment optical path is used to match the beam characteristics of the light source with the beam characteristics of the passive triangular resonant cavity 6; the collimation matching alignment optical path includes a collimation lens group 2 connected to the laser light source 1 and an alignment lens group 5 connected to the passive triangular resonant cavity 6, and a matching lens group 3 and a beam splitter are provided between the collimation lens group 2 and the alignment lens group 5 along the optical path direction; the alignment lens group 5 includes a first alignment lens group 501 and a second alignment lens group 502 arranged in parallel, and the light source is divided into a first light beam and a second light beam at the beam splitter, and the first light beam is used to be injected into the passive triangular resonant cavity 6, and the first light beam at the beam splitter is used to be injected into the passive triangular resonant cavity 6. After being incident on the alignment lens group 5, it is aligned twice by the first alignment lens group 501 and the second alignment lens group 502 and then emitted in parallel into the passive triangular resonant cavity 6. The alignment of the light path of the light source and the light path of the passive triangular resonant cavity 6 is achieved through the cooperation of the first alignment lens 501 and the second alignment lens 502; the matching lens group includes a conventional Galilean telescope group 301 and a cylindrical lens 302. The conventional Galilean telescope group 301 can adjust the beam waist in the meridian and sagittal planes to the same degree, and the cylindrical lens 302 can achieve different degrees of adjustment of the elliptical beam in different meridian and sagittal planes.

[0042] The passive triangular resonant cavity 6 is used to receive the energy of the light source, achieve the resonance condition, realize the accumulation of light energy, and realize the establishment of the resonance peak; Figure 1 and Figure 2 As shown, the passive triangular resonant cavity 6 includes a first cavity mirror 7 with a plane mirror structure, a first cavity mirror 7 and a third cavity mirror 9 with a curved structure. The optical path between the first cavity mirror 7, the second cavity mirror 8 and the third cavity mirror 9 forms a triangular cavity closed optical axis loop; the first light beam enters the passive triangular resonant cavity 6 from the first cavity mirror 7, and completes a cycle through the second cavity mirror 8 and the third cavity mirror 9; the passive triangular resonant cavity 6 also includes an air inlet 13, an air outlet 15, a gas filter 14, a cavity temperature measurer 16 and a cavity pressure measurer 17.

[0043] The passive triangular resonant cavity 6 is also connected to a resonance establishing mechanism and a cavity length servo control mechanism 19. The resonance establishing mechanism is used to scan the cavity length and make the passive triangular resonant cavity 6 meet the resonance condition, and the cavity length servo control mechanism 19 is used to realize cavity length adjustment; the resonance establishing mechanism is used to scan the cavity length so that the resonant cavity meets the resonance condition. The resonance establishing mechanism includes a piezoelectric ceramic 18 bonded to the third cavity mirror 9, and the cavity length servo control mechanism 19 is connected to the piezoelectric ceramic 18. The cavity length servo control mechanism 19 controls the piezoelectric ceramic 18 to realize cavity length adjustment to achieve the resonance condition, accumulate the light intensity in the cavity, and rapidly enhance the light intensity of the transmitted light beam; the passive triangular resonant cavity 6 completes the closed optical axis design and realizes the preliminary alignment of the triangular mirror.

[0044] An optical amplifier 22 is included between the alignment lens assembly 5 and the passive triangular resonant cavity 6 to enhance the energy of the transmitted light at the resonant frequency in the passive triangular resonant cavity 6 ; the detector 11 is used to obtain the energy of the light emitted from the passive triangular resonant cavity 6 .

[0045] The focusing mirror 10 is used to converge the light emitted by the passive triangular resonant cavity 6 onto the detector 11; the data acquisition, recording and analysis mechanism 12 is used to obtain the tilt and axial translation errors between the optical axis of the light source and the optical axis in the passive triangular resonant cavity 6; the light intensity information measured by the detector 11 can be recorded, and the light intensity information within a free spectrum range is recorded starting from the first resonance; the intensity information of the first-order mode excitation is obtained by the collected light intensity information; including obtaining the recording starting when the first resonance peak is reached, and when the wavelength of the light source scans a free spectrum range to the second resonance peak, the data recording mechanism obtains the cavity transmission intensity information within a free light range, and since the first-order mode resonance frequency is known, the excitation intensity information at the two first-order mode resonance points is obtained, and the misalignment errors of the two planes are respectively obtained from the excitation intensities of the two first-order modes.

[0046] A reference light modulation mechanism 20 is also connected between the spectrometer and the cavity length servo mechanism. The second optical path enters the reference light modulation mechanism 20 to achieve frequency stabilization. The second light beam at the spectrometer is added to the frequency sideband through the reference light modulation mechanism 20 and mixed with the light beam emitted from the passive triangular resonant cavity 6 to achieve stable matching between the frequency in the cavity and the frequency of the light source.

[0047] The operating principle is as follows: Light emitted by a laser light source 1 passes through a collimating lens assembly 2 and a matching lens assembly 3, achieving beam matching with the light beam in a ring-shaped passive triangular resonator 6, which has a closed optical axis design. When intracavity resonance is not established, the detector 11 cannot detect the light intensity emitted from the passive triangular resonator 6. The resonance establishment mechanism uses a cavity length servo control mechanism 19 connected to the third cavity mirror 9 to scan the cavity length. During the cavity length scanning process, when the cavity length of the passive triangular resonator 6 meets the resonance condition, the light intensity detected by the detector 11 rapidly accumulates. After reaching a peak, the cavity length servo control mechanism 19 stops scanning. At this point, the light source modulation mechanism 20 begins scanning the light source wavelength, and the data acquisition, recording, and analysis mechanism 12 begins recording the transmitted light intensity information, stopping recording when the wavelength scan reaches the next resonance peak. By acquiring the transmission intensity information of two first-order modes within a free spectrum range, the misalignment error information in the ring-down spectroscopy device can be obtained.

[0048] A method for measuring the misalignment error of a ring cavity ring-down spectroscopy device, using the above-mentioned measurement device for testing, comprises the following steps:

[0049] S1: Make the annular cavity optical path meet the closed optical axis characteristics: by designing the cavity length, cavity angle and curvature of the third cavity mirror 9 in the triangular cavity closed optical axis loop to meet the resonant cavity stability condition and closed optical axis condition;

[0050] S2: Make the laser light source 1 and the passive triangular resonant cavity 6 meet the preliminary alignment conditions: the light emitted by the laser light source 1 passes through the center of the collimating lens group 2 and the matching lens group 3 in sequence, the first light beam passing through the beam splitter and then through the alignment lens group 5 into the center of the first cavity mirror 7 in the passive triangular resonant cavity 6, and achieves preliminary alignment with the optical axis in the passive triangular resonant cavity.

[0051] S3: The passive triangular resonant cavity 6 is made to meet the resonance condition and establish the threshold light intensity through the cavity length servo control mechanism 19; the light emitted by the light source enters the passive triangular resonant cavity 6 through the matching mirror group 3 and the alignment mirror group 5. When the passive triangular resonant cavity 6 does not meet the resonance condition, the light energy received by the detector 11 after passing through the focusing mirror 10 is weak, and the detector 11 does not respond; at this time, the cavity length servo control mechanism 19 controls the piezoelectric ceramic 18 and realizes cavity length adjustment; when the passive triangular resonant cavity meets the resonance condition, the light energy in the passive triangular resonant cavity accumulates rapidly, and the detector 11 realizes the establishment of the output light intensity; at the same time, in order to maintain the stability of the resonance phenomenon and overcome the influence of the light source fluctuation, the reference light modulation mechanism 20 is used to add a frequency sideband to the second light beam, and mix it with the output light beam from the passive triangular resonant cavity 6 to achieve long-term stable matching of the cavity frequency and the light source frequency.

[0052] S4: After the resonance is established, the light source performs a wavelength scan in a free spectrum range, and the data acquisition, recording and analysis mechanism 12 records the transmitted light intensity information within a wavelength range.

[0053] The free spectral range (FSR) can be calculated using formula (3), where c is the speed of light and L is the cavity length of the triangular cavity (i.e., the sum of the lengths of the three sides).

[0054] FSR=c / nL (3)

[0055] S5: Obtaining the imbalance information through the transmitted light intensity data. The data acquisition, recording, and analysis unit 12 analyzes the recorded transmitted light intensity information. Specifically, the peak value when the resonance is first reached is taken as the zero point, and two sub-peaks between the peak value and the next peak value are selected for analysis; the two sub-peaks are the TEM01 mode and the TEM10 mode. The resonant frequencies of the TEM01 mode and the TEM10 mode are calculated using formulas (1) and (2), respectively:

[0056]

[0057]

[0058] Wherein, FSR is the free spectral range of the passive triangular resonant cavity 6 , L is the cavity length of the passive triangular resonant cavity 6 , and R is the curvature radius of the third cavity mirror 9 .

[0059] Due to the use of the optical amplifier 22, the first-order mode is strongly excited, and there is strong transmitted light energy at the resonant frequencies of the TEM01 mode and TEM10 mode respectively. The detuning information corresponding to the transmitted light intensity can be obtained by formula (4).

[0060] Where I1 is the first-order mode transmitted light intensity, I0 is the fundamental mode transmitted light intensity (i.e. the strongest light intensity when the resonance is initially established), ε is the axis translation of the misalignment, α is the tilt of the misalignment, and q L is the q parameter of the light source (the light source parameters are known).

[0061] The excitation amount of the TEM01 mode corresponds to the misalignment amount in the meridional plane, and the excitation amount of the TEM10 mode corresponds to the misalignment amount in the sagittal plane. The misalignment amounts of the two orthogonal planes correspond to the transmitted light intensity information at different resonant frequencies, thereby realizing the acquisition of misalignment information in different planes.

[0062] I1 / I0=·(2πe -2 ) -1 / 2 (ε-q L α) 2 (4)

[0063] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not constitute a limitation of the present invention.

[0064] It should be understood that the various forms of the processes shown above can be used to reorder, add, or delete steps. For example, the steps described in the present disclosure can be performed in parallel, sequentially, or in a different order, as long as the desired results of the technical solutions disclosed in the present disclosure can be achieved. This is not limited herein.

[0065] The above specific embodiments do not limit the scope of protection of the present invention. Those skilled in the art will appreciate that various modifications, combinations, sub-combinations, and substitutions may be made based on design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention are intended to be included within the scope of protection of the present invention.

Claims

1. A device for measuring misalignment errors of a ring cavity ring-down spectroscopy device, characterized by: The invention comprises a laser light source (1), a collimation matching alignment optical path, a passive triangular resonant cavity (6), a focusing mirror (10), a detector (11) and a data acquisition, recording and analysis mechanism (12) which are sequentially arranged along the incident direction of the light source to the emitting direction of the light source; the laser light source (1) comprises a light source part and a wavelength tuning part, which are used to realize the emission of the light source and the scanning of the wavelength of the light source; The passive triangular resonant cavity (6) is used to receive the energy of the light source to establish the resonance peak, and the collimation matching alignment optical path is used to match the beam characteristics of the light source with the beam characteristics of the passive triangular resonant cavity (6); the detector (11) is used to obtain the energy of the light emitted by the passive triangular resonant cavity (6); the data acquisition, recording and analysis mechanism (12) is used to obtain the tilt and axis translation errors between the optical axis of the light source and the optical axis in the passive triangular resonant cavity (6); the passive triangular resonant cavity (6) is also connected to a resonance establishment mechanism and a cavity length servo control mechanism (19), the resonance establishment mechanism is used to scan the cavity length and make the passive triangular resonant cavity (6) meet the resonance condition, and the cavity length servo control mechanism (19) is used to achieve cavity length adjustment; The passive triangular resonant cavity (6) comprises a first cavity mirror (7) and a second cavity mirror (8) of a plane mirror structure, and a third cavity mirror (9) of a curved surface structure, wherein the optical path between the first cavity mirror (7), the second cavity mirror (8) and the third cavity mirror (9) forms a triangular cavity closed optical axis loop; the resonance establishment mechanism comprises a piezoelectric ceramic (18) bonded to the third cavity mirror (9), and a cavity length servo control mechanism (19) is connected to the piezoelectric ceramic (18), and the cavity length servo control mechanism (19) controls the piezoelectric ceramic (18) to achieve cavity length adjustment; The collimation matching alignment optical path comprises a collimation lens group (2) connected to the laser light source (1) and an alignment lens group (5) connected to the passive triangular resonant cavity (6), and a matching lens group (3) and a beam splitter are provided between the collimation lens group (2) and the alignment lens group (5) along the optical path direction; The alignment lens group (5) comprises a first alignment lens group (501) and a second alignment lens group (502) arranged in parallel. After the first light beam at the spectroscope is incident on the alignment lens group (5), it is aligned twice by the first alignment lens group (501) and the second alignment lens group (502) and then emitted in parallel into the passive triangular resonant cavity (6).

2. The detuning error measuring device for a ring cavity ring-down spectroscopy device according to claim 1, characterized in that: A reference light modulation mechanism (20) is also connected between the spectroscope and the cavity length servo control mechanism (19). The second light beam at the spectroscope is added to the frequency sideband through the reference light modulation mechanism (20) and mixed with the light beam emitted from the passive triangular resonant cavity (6) to achieve stable matching between the frequency in the cavity and the frequency of the light source.

3. The detuning error measuring device for a ring cavity ring-down spectroscopy device according to claim 2, characterized in that: An optical amplifier (22) is included between the alignment lens group (5) and the passive triangular resonant cavity (6) for enhancing the energy of transmitted light at the resonant frequency in the passive triangular resonant cavity (6).

4. The device for measuring misalignment error of a ring cavity ring-down spectroscopy device according to any one of claims 1 to 3, characterized in that: The passive triangular resonant cavity (6) further comprises an air inlet (13), an air outlet (15), a gas filter (14), a cavity temperature measuring device (16), and a cavity pressure measuring device (17).

5. A method for measuring the misalignment error of a ring cavity ring-down spectroscopy device, using the measuring device according to claim 4 for testing, characterized in that: The steps include: S1: Make the annular cavity optical path meet the closed optical axis characteristics: by designing the cavity length, cavity angle and curvature of the third cavity mirror (9) in the triangular cavity closed optical axis loop to meet the resonant cavity stability condition and closed optical axis condition; S2: Make the laser light source (1) and the passive triangular resonant cavity (6) meet the preliminary alignment conditions: the light emitted by the laser light source (1) passes through the center of the collimating lens group (2) and the matching lens group (3) in sequence, passes through the first light beam of the beam splitter, and then passes through the alignment lens group (5) to enter the center of the first cavity mirror (7) in the passive triangular resonant cavity (6), and achieves preliminary alignment with the optical axis in the passive triangular resonant cavity; S3: The passive triangular resonant cavity (6) is made to meet the resonance condition and establish the threshold light intensity through the cavity length servo control mechanism (19); S4: After the resonance is established, the light source realizes a wavelength scan in a free spectrum range, and the transmitted light intensity information in a wavelength range is recorded by the data acquisition, recording and analysis mechanism (12); S5: Obtain misalignment information through the transmitted light intensity data.

6. The method for measuring misalignment error of a ring cavity ring-down spectroscopy device according to claim 5, characterized in that: The light emitted by the light source passes through the matching lens group (3) and the alignment lens group (5) and enters the passive triangular resonant cavity (6). In step S3, when the passive triangular resonant cavity (6) does not meet the resonance condition, the light energy received by the detector (11) after passing through the focusing lens (10) is weak, and the detector (11) does not respond. At this time, the cavity length servo control mechanism (19) controls the piezoelectric ceramic (18) and realizes cavity length adjustment. When the passive triangular resonant cavity meets the resonance condition, the light energy in the passive triangular resonant cavity accumulates rapidly, and the detector (11) realizes the establishment of the output light intensity.

7. The method for measuring misalignment error of a ring cavity ring-down spectroscopy device according to claim 6, wherein: In S5, the peak value when the resonance is first reached is taken as the zero point, and two sub-peaks between the peak value and the next peak value are selected for analysis; the two sub-peaks are the TEM01 mode and the TEM10 mode. The resonant frequencies of the TEM10 mode and the TEM01 mode are calculated by formula (1) and formula (2), respectively: Wherein, FSR is the free spectral range of the passive triangular resonant cavity (6), L is the cavity length of the passive triangular resonant cavity (6), and R is the curvature radius of the third cavity mirror (9).

Images