A passive ring-down cavity alignment method based on vibration spectrum positioning

Abstract

The present invention provides a passive ring-down cavity alignment method based on vibration spectrum positioning. First, a passive ring-down cavity is built, and a continuous wave detection beam is injected from one end of the passive ring-down cavity. A photoelectric device is used at the other end to obtain a passive ring-down cavity transmission signal. Next, a specific frequency of vibration is applied to a cavity mirror at one end in the horizontal and vertical directions respectively, and the passive ring-down cavity transmission signal collected while adjusting the cavity mirror at the other end is analyzed by spectrum. Vibration spectrum positioning is performed until a characteristic vibration spectrum appears, and the collimation of the cavity mirror at the other end relative to the incident beam is completed; after the cavity mirror is aligned, a specific frequency of vibration is applied to it and the above process is repeated to complete the alignment of the cavity mirrors at both ends of the passive ring-down cavity. This method completes the passive ring-down cavity alignment process based on vibration spectrum positioning, has the characteristics of distinct characteristics and convenient operation, and at the same time, this method has extremely high theoretical accuracy, which is of great significance for the application of optical cavity ring-down technology.

Description

Technical Field

[0001] The invention relates to the field of laser technology, and in particular to a passive ring-down cavity alignment method based on vibration spectrum positioning. Background Art

[0002] The ring-down cavity is a typical passive resonant cavity and the core component of the cavity ring-down technology. In the cavity ring-down technology, the ring-down cavity is responsible for accumulating laser energy and generating a cavity ring-down signal. The cavity ring-down signal contains observation information such as the loss factor in the cavity, which is the key to the measurement of the cavity ring-down technology. A series of studies in recent years have shown that the observed value of the cavity loss factor is extremely sensitive to the alignment state of the ring-down cavity. If the adjustment state of the ring-down cavity is inconsistent during the measurement of the cavity ring-down technology, a relative observation error of the cavity loss factor may occur. Therefore, in the application of cavity ring-down technology measurement, it is extremely important to ensure that the alignment state of the ring-down cavity remains consistent throughout the process.

[0003] In terms of ring-down cavity tuning, the main technical challenge is that the existing cavity tuning evaluation indicators generally show nonlinear multi-extreme distribution characteristics with the cavity misalignment parameters (Xue Ying, Du Xinghu, He Xing, et al., Optical cavity ring-down tuning method based on transmission spot morphology monitoring, Chinese Journal of Lasers, 2020, 47(5): 0504001; Hamzhe T, Anam P, Liu J, Aligning an optical cavity: with reference to cavity ring-down spectroscopy, Applied Optics, 2020, 59(30): 9464), which makes the cavity tuning very easy to fall into local optimization. Therefore, it is necessary to develop a cavity tuning criterion that can overcome local optimization. In view of the responsiveness of the ring-down cavity to the input vibration signal (Chinese Patent Application No. 202111518691.0, "A Vibration Detection Method Based on Optical Cavity Ring-Down Technology"), spectral analysis of the transmission signal of the ring-down cavity shows that by locating the characteristic spectrum of the input vibration, the absolutely non-misaligned position of the cavity mirror can be accurately determined, thereby developing a cavity tuning criterion that theoretically has only a single extreme value, thereby achieving precise alignment adjustment of the ring-down cavity. Summary of the invention

[0004] The technical problem to be solved by the present invention is that the current tuning criteria of the ring-down cavity all have multi-extreme characteristics, which easily lead to local optimization, increase the difficulty of collimating the cavity, and make it difficult to obtain an absolutely non-detuned state of the ring-down cavity.

[0005] The technical solution adopted by the present invention to solve the technical problem is: a ring-down cavity alignment method based on vibration spectrum positioning, and the specific implementation steps are as follows:

[0006] Step (1), constructing a passive ring-down cavity, injecting a laser beam into one end of the passive ring-down cavity, and detecting and recording the output signal of the ring-down cavity with a photoelectric response device at the other end;

[0007] The ring-down cavity output signal detected by the photoelectric response device is a ring-down cavity transmission light intensity signal.

[0008] Step (2), apply vibrations of specific frequencies to the cavity mirror at one end in the horizontal direction and the vertical direction respectively, and adjust the cavity mirror at the other end at the same time. In this process, the vibration spectrum of the cavity output signal is monitored using a photoelectric response device. The vibration frequency is located according to the monitoring results until a characteristic vibration spectrum appears, and it can be considered that the alignment adjustment of the cavity mirror at the other end is completed;

[0009] Step (3), apply a specific frequency vibration to the other end cavity mirror and repeat the above process until the characteristic spectrum appears, then it can be considered that the collimation adjustment of the cavity mirrors at both ends has been completed.

[0010] During the ring-down cavity alignment process, the cavity mirror adjustment includes angle adjustment and position adjustment.

[0011] The vibration applied to the cavity mirror should be a narrow-band vibration with a constant frequency, and its characteristic spectrum should be approximately twice the input vibration frequency and its harmonics, and there should be no approximately identical frequency to the input vibration.

[0012] The principle of the present invention is that the response spectrum of the ring-down cavity to the vibration signal has the uniqueness of the characteristic spectrum in the state of absolutely no detuning (i.e., strict collimation). Based on the spectrum response capability of the ring-down cavity to the input vibration signal, a vibration light signal of a characteristic frequency is injected into the ring-down cavity, and the ring-down cavity collimation adjustment is completed by performing spectrum analysis and vibration spectrum positioning on the transmission signal until the characteristic spectrum of the input vibration signal appears.

[0013] Compared with the prior art, the present invention has the following advantages: the method has distinct characteristics and is easy to operate; at the same time, the method has extremely high theoretical accuracy, which is of great significance for the application of optical cavity ring-down technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of a device of a multi-beam axis difference detection method based on a passive cavity loss model of the present invention;

[0015] Figure 2 A vibration signal applied to a cavity mirror in a passive ring-down cavity alignment method based on vibration spectrum positioning according to the present invention;

[0016] Figure 3 The vibration spectrum monitoring result of a ring-down cavity alignment method based on vibration spectrum positioning when the cavity parameters are misaligned is disclosed in the present invention;

[0017] Figure 4 The present invention relates to a ring-down cavity alignment method based on vibration spectrum positioning when the ring-down cavity is strictly aligned. DETAILED DESCRIPTION

[0018] The following is combined with Figure 1 And specific implementation modes further illustrate the present invention.

[0019] like Figure 1 As shown, a ring-down cavity alignment method based on vibration spectrum positioning of the present invention is specifically implemented in the following steps:

[0020] Step (1), constructing a passive ring-down cavity, injecting a laser beam into one end of the passive ring-down cavity, and detecting and recording the output signal of the ring-down cavity with a photoelectric response device at the other end;

[0021] In this embodiment, the passive ring-down cavity is a two-mirror straight cavity, the injected light beam is 1064nm, the photoelectric response device is a high-speed photodetector that can record the passive ring-down cavity transmitted light intensity signal, and the processor is an oscilloscope in conjunction with a host computer.

[0022] Step (2), apply vibrations of specific frequencies to the cavity mirror at one end in the horizontal direction and the vertical direction respectively, and adjust the cavity mirror at the other end at the same time. In this process, the vibration spectrum of the cavity output signal is monitored using a photoelectric response device. The vibration frequency is located according to the monitoring results until a characteristic vibration spectrum appears, and it can be considered that the alignment adjustment of the cavity mirror at the other end is completed;

[0023] The specific implementation method of this step (2) is as follows:

[0024] Apply the following to the cavity mirror M2 in the x direction: Figure 2 The vibration signal shown in the figure (the vibration frequency is 78125Hz). The transmission signal of the ring-down cavity is collected and recorded by a high-speed photodetector, and the oscilloscope cooperates with the host computer to perform Fourier transform to complete the signal spectrum analysis and obtain the signal spectrum. After obtaining the spectrum information, the vibration spectrum peak is located, and the signal with the lowest frequency in a series of vibration spectrum peaks is used as the cavity tuning feedback to adjust the x direction of the cavity mirror M1.

[0025] The specific example of this embodiment is as follows: When the cavity mirror M1 is misaligned in the x direction, the recorded signal spectrum is as follows: Figure 3 As shown in FIG. 1 , a signal of approximately the same frequency as the injected vibration signal (the lowest frequency corresponding to the spectrum signal peak is about 76290 Hz) and its higher harmonics can be obtained; when the cavity mirror M1 is strictly aligned in the x direction, the signal spectrum recorded is as follows: Figure 4As shown in the figure, only the approximately double frequency signal of the injected signal and its higher harmonics can be obtained (the lowest signal frequency corresponding to the spectrum signal peak is about 152600Hz). Therefore, as long as there is a signal of approximately the same frequency as the input vibration in the monitoring spectrum, it can be considered that the cavity parameters of the ring-down cavity are still misaligned, and it is necessary to continue to adjust until only the approximately double frequency signal exists.

[0026] Next, a vibration signal is applied to the cavity mirror M2 in the y direction, and the y direction adjustment of the cavity mirror M1 is completed according to the steps and methods described above.

[0027] Step (3), apply a specific frequency vibration to the other end cavity mirror and repeat the above process until the characteristic spectrum appears, then it can be considered that the collimation adjustment of the cavity mirrors at both ends has been completed.

[0028] The specific implementation method of this step (3) is described as follows: after the adjustment of M1 is completed, vibration signals are applied to the x and y directions of M1 respectively, and the spectrum information of the ring-down cavity transmission signal is obtained by the same signal recording and analysis method, and the x and y directions of the cavity mirror M2 are adjusted respectively according to the spectrum positioning.

[0029] The contents not described in detail in the specification of the present invention belong to the prior art known to the professional and technical personnel in this field.

Claims

1. A passive ring-down cavity alignment method based on vibration spectrum positioning, characterized in that: The implementation steps are as follows: Step (1), constructing a passive ring-down cavity, injecting a laser beam into one end of the passive ring-down cavity, and detecting and recording the output signal of the ring-down cavity with a photoelectric response device at the other end; Step (2), applying vibrations of specific frequencies to the cavity mirror at one end in the horizontal direction and the vertical direction respectively, and adjusting the cavity mirror at the other end at the same time. In this process, the vibration spectrum of the cavity output signal is monitored by a photoelectric response device, and the vibration frequency is located according to the monitoring result until a characteristic vibration spectrum appears, and it can be considered that the collimation adjustment of the cavity mirror at the other end is completed; Step (3), then apply a specific frequency vibration to the other end cavity mirror and repeat the above process until a characteristic vibration spectrum appears, then it can be considered that the two end cavity mirrors have completed the alignment adjustment; the characteristic vibration spectrum described in step (2) and step (3) is the approximate double frequency of the input vibration frequency and its harmonics, and there is no approximate same frequency as the input vibration.

2. According to claim 1, a passive ring-down cavity alignment method based on vibration spectrum positioning is characterized in that: During the ring-down cavity alignment process, the cavity mirror adjustment includes angle adjustment and position adjustment.

3. The passive ring-down cavity alignment method based on vibration spectrum positioning according to claim 1 is characterized in that: The ring-down cavity output signal detected by the photoelectric response device in step (1) is a ring-down cavity transmission light intensity signal.

4. The passive ring-down cavity alignment method based on vibration spectrum positioning according to claim 1 is characterized in that: The vibration applied to the cavity mirror in step (2) and step (3) should be a narrow-band vibration with a constant frequency.

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