A method for measuring the hysteresis effect of highly reflective tilt mirrors

Abstract

The present invention provides a method for measuring the hysteresis effect of a high-reflection tilt mirror, wherein the high-reflection tilt mirror to be measured is used as a ring-down cavity mirror, and forward and reverse driving are applied to the tilt mirror respectively, and the intracavity loss change in the process is recorded. The actual angle tilt amount in the tilt mirror driving process can be solved by the intracavity loss change law, thereby completing the hysteresis effect measurement of the tilt mirror in forward and reverse driving. The method is based on the high sensitivity characteristics of the optical cavity ring-down technology, and by constructing the mathematical relationship between the intracavity loss of the ring-down cavity and the tilt angle of the cavity mirror, the high-sensitivity measurement of the hysteresis effect of the high-reflection tilt mirror is achieved, and it can be used as an effective means for testing the relevant performance of the high-reflection tilt mirror.

Description

Technical Field

[0001] The present invention relates to the field of laser technology, and in particular to a method for measuring the hysteresis effect of a high-reflection tilt mirror, which can be applied to the fields of adaptive optics, space optical communication, astronomical telescopes, etc. Background Art

[0002] The tilt mirror is one of the important devices in the fields of adaptive optics and space optical communications. It can generate high-speed tilt by itself to compensate for the tilt aberration caused by factors such as atmospheric turbulence. Due to the hysteresis characteristics of the driving material of the tilt mirror itself, it may affect the closed-loop control of the tilt mirror in practical applications. Taking the piezoelectric tilt mirror as an example, the displacement curve of its driving material, piezoelectric ceramic, does not overlap during the boost and buck process (Liu Xin, Li Xinyang, Du Rui, Hysteresis nonlinear modeling and quasi-compensation control of piezoelectric tilt mirror, Optoelectronic Engineering, 2020(47), 4, 180654), which leads to the hysteresis effect. In order to effectively compensate for the hysteresis effect, it is of great significance to measure the hysteresis effect with high sensitivity.

[0003] There is currently a lack of high-precision and high-sensitivity technical means for measuring the hysteresis effect of tilt mirrors. At present, the main measurement methods all rely on the spot positioning of the detection beam (Chinese patent CN110530612A, "A system and test method for testing tilt mirrors using PSD"; Chinese patent CN104215431A, "A fast tilt mirror performance test device"). In practical applications, the measurement accuracy of the above methods will be limited by the pixel size or system complexity of the array detector, and it is difficult to achieve high precision and high sensitivity requirements. In the case of limited measurement accuracy and sensitivity, research on hysteresis effects often requires the use of hysteresis nonlinear models. However, traditional theoretical models face the disadvantages of difficult parameter solution and high computational complexity, which limits the compensation accuracy and practical effect.

[0004] In view of this, the present invention utilizes the fact that the cavity loss of the ring-down cavity is extremely sensitive to the misalignment angle of the cavity mirror and the characteristics of the ring-down cavity with high precision and high sensitivity detection capability, and can achieve high sensitivity and high precision measurement of the hysteresis effect of the high-reflection tilt mirror. The present invention uses the tilt mirror as one of the cavity mirrors of the folded cavity optical cavity ring-down system, and uses the tilt mirror angle as the cavity mirror angle misalignment. According to the change in the observed value of the cavity loss, the hysteresis effect curve of the high-reflection tilt mirror in the forward and reverse driving process can be obtained. This method can improve the measurement accuracy and measurement sensitivity of the hysteresis effect of the high-reflection tilt mirror, which is of great value to the development, testing and application of related devices, and can also provide help for the hysteresis nonlinear effect model and theoretical research. Summary of the invention

[0005] The technical problem to be solved by the present invention is to measure the hysteresis effect of a high-reflection tilt mirror with high precision and high sensitivity.

[0006] The technical solution adopted by the present invention to solve the technical problem is:

[0007] A method for measuring the hysteresis effect of a highly reflective tilt mirror, the specific implementation steps are as follows:

[0008] Step (1), constructing an optical cavity ring-down system, including a laser light source, a coupling cavity mirror, a plano-concave cavity mirror, a photodetector, a high-reflection tilt mirror to be measured, a data acquisition module and a processor, wherein the plano-concave cavity mirror, the coupling cavity mirror and the high-reflection tilt mirror to be measured constitute a folded ring-down cavity, the laser light source emits a laser beam, which enters the ring-down cavity through the coupling cavity mirror, and the light intensity signal in the ring-down cavity is transmitted through the plano-concave cavity mirror into the photodetector. The transmission signal of the ring-down cavity detected by the photodetector is processed by the data acquisition module and the processor.

[0009] Step (2), injecting a laser beam into the ring-down cavity, and simultaneously using a photodetector and a data acquisition module to monitor and record the transmission signal in the cavity in real time.

[0010] Step (3), applying forward and reverse drive to the tilt mirror to be tested respectively, each time the drive is applied, collecting the corresponding transmission signal and processing it through a processor to obtain the cavity loss, and the hysteresis effect can be measured based on the change curve of the cavity loss with forward and reverse drive.

[0011] Furthermore, the laser light source described in step (1) is a continuous wave laser, whose output center wavelength λ is equal to the reflectivity R of the high reflective tilt mirror at this wavelength. λ R λ ≥99.8%.

[0012] Furthermore, the concave curvature radius ρ of the plano-concave cavity mirror described in step (1) and the cavity length L of the ring-down cavity should satisfy ρ>L.

[0013] Furthermore, the photoelectric detector and data acquisition module described in step (2) need to have a high working bandwidth, and the combined working bandwidth should be no less than 1 MHz.

[0014] Furthermore, the specific characterization index of the intracavity loss in step (3) may be one of the intracavity loss factor, the optical cavity ring-down time constant, the cavity quality factor and the cavity finesse coefficient.

[0015] Furthermore, the hysteresis effect measurement result described in step (3) can be a curve of the change of the intra-cavity loss with the driving amount of the tilt mirror, or the actual angle and driving displacement of the tilt mirror can be solved by the intra-cavity loss to obtain a curve of the change of the actual angle and driving displacement with the driving amount of the tilt mirror.

[0016] The principle of the present invention is that the optical cavity ring-down technology has high-precision and high-sensitivity measurement capabilities. In this technology, the intracavity loss of the ring-down cavity is extremely sensitive to the cavity mirror misalignment angle. By converting the tilt mirror angle execution amount into the cavity mirror angle misalignment amount, a high-sensitivity cavity loss change curve can be obtained. The comprehensive measurement of the hysteresis effect can be achieved by the cavity loss change law during the forward and reverse changes of the tilt mirror tilt angle.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] This method has the characteristics of simple structure, convenient operation, high precision and high sensitivity. At the same time, this detection method can realize a relatively compact optical path layout and has strong compatibility with high-reflection tilt mirrors of various calibers and specifications. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of a device for measuring the hysteresis effect of a high-reflection tilt mirror of the present invention, wherein 1 is a laser light source, 2 is a coupling cavity mirror, 3 is a plano-concave cavity mirror, 4 is a photoelectric detector, 5 is a high-reflection tilt mirror to be measured, 6 is a data acquisition module, and 7 is a processor;

[0020] Figure 2 This is an example diagram of hysteresis effect measurement results of a method for measuring the hysteresis effect of a high-reflection tilt mirror involved in the present invention. DETAILED DESCRIPTION

[0021] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0022] like Figure 1 As shown, a method for measuring the hysteresis effect of a highly reflective tilt mirror of the present invention is specifically implemented as follows:

[0023] Step (1), building an optical cavity ring-down system, including a laser light source 1, a coupling cavity mirror 2, a plano-concave cavity mirror 3, a photodetector 4, a high-reflection tilt mirror 5 to be measured, a data acquisition module 6 and a processor 7, wherein the plano-concave cavity mirror 3, the coupling cavity mirror 2 and the high-reflection tilt mirror 5 to be measured constitute a folded ring-down cavity, the laser light source 1 emits a laser beam, which enters the folded ring-down cavity through the coupling cavity mirror 2, and the light intensity signal in the folded ring-down cavity is transmitted through the plano-concave cavity mirror 3 and enters the photodetector 4. The ring-down cavity transmission signal detected by the photodetector 4 is handed over to the data acquisition module 6 and the processor 7 for processing. The laser light source 1 is a continuous wave laser, and its output center wavelength λ is consistent with the reflectivity R of the high-reflection tilt mirror 5 to be measured at this wavelength. λ R λ ≥99.8%. The curvature radius ρ of the plano-concave cavity mirror 3 is about 1m, and the length L of the ring-down cavity is about 0.45m, satisfying the relationship ρ>L.

[0024] In this embodiment, the laser light source 1 is a continuous wave laser with a central wavelength of 1064 nm, and the high-reflection tilt mirror 5 to be tested is a piezoelectric ceramic driven tilt mirror, and its reflectivity in the 1064 nm band is greater than 99.9%.

[0025] Step (2), injecting a laser beam into the ring-down cavity to be tested, and simultaneously using the photodetector 4 and the data acquisition module 6 to monitor and record the transmission signal in the cavity in real time.

[0026] In this embodiment, the photodetector 4 is a high-speed avalanche photodiode, the working bandwidth is greater than 10 MHz, the sampling frequency of the data acquisition module 6 is 80 MHz, and the device response time is less than 10 ns.

[0027] Step (3), applying forward and reverse drive to the high-reflection tilt mirror 5 to be measured respectively. Each time the drive is applied, the corresponding transmission signal is collected and processed by the processor 7 to obtain the cavity loss. The hysteresis effect can be measured based on the change curve of the cavity loss with forward and reverse drive.

[0028] In this embodiment, the cavity loss is characterized by the cavity ring-down time constant. The cavity ring-down time constant variation result is obtained by applying a ±0.004° drive to the high-reflection tilt mirror 5 to be tested. Figure 2 As shown. Figure 2 The hysteresis effect can be observed in the cavity ring-down time constant. The specific calculation process of the cavity ring-down time constant is: collect the cavity ring-down signal of sufficient length and fit the signal according to the single exponential decay function. The light intensity ring-down time constant can be extracted from the fitting parameters.

[0029] If the intrinsic loss of the ring-down cavity is further reduced and the working bandwidth of the photodetector 4 and the data acquisition module 6 is increased, the measurement accuracy and measurement sensitivity can be further improved.

[0030] 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 method for measuring the hysteresis effect of a highly reflective tilt mirror, characterized in that: The implementation steps are as follows: Step (1), constructing an optical cavity ring-down system, including a laser light source, a coupling cavity mirror, a plano-concave cavity mirror, a photodetector, a high-reflection tilt mirror to be measured, a data acquisition module and a processor, wherein the plano-concave cavity mirror, the coupling cavity mirror and the high-reflection tilt mirror to be measured constitute a folded ring-down cavity, the laser light source emits a laser beam, which enters the ring-down cavity through the coupling cavity mirror, the light intensity signal in the ring-down cavity is transmitted through the plano-concave cavity mirror into the photodetector, and the ring-down cavity transmission signal detected by the photodetector is processed by the data acquisition module and the processor; the laser light source is a continuous wave laser, and its output center wavelength is λ The reflectivity of the highly reflective tilted mirror at this wavelength R λ Should satisfy R λ ≥99.8%; the curvature radius of the concave surface of the plano-concave cavity mirror ρ Ring-down cavity length L Should meet ρ > L ; Step (2), injecting a laser beam into the ring-down cavity, and simultaneously using a photodetector and a data acquisition module to monitor and record the ring-down cavity transmission signal in real time; Step (3), applying forward and reverse driving to the tilt mirror to be measured respectively, each time the driving is applied, collecting the corresponding ring-down cavity transmission signal and processing it through a processor to obtain the cavity loss, and the hysteresis effect can be measured based on the change curve of the cavity loss with the forward and reverse driving.

2. A method for measuring the hysteresis effect of a highly reflective tilt mirror according to claim 1, characterized in that: The photoelectric detector and data acquisition module described in step (2) need to have a high working bandwidth, and the combined working bandwidth should be no less than 1 MHz.

3. The method for measuring the hysteresis effect of a highly reflective tilt mirror according to claim 1, characterized in that: The specific characterization index of the intracavity loss in step (3) may be one of the intracavity loss factor, the optical cavity ring-down time constant, the cavity quality factor and the cavity finesse coefficient.

4. The method for measuring the hysteresis effect of a highly reflective tilt mirror according to claim 1, characterized in that: The hysteresis effect measurement result described in step (3) can be a curve of the change of the intracavity loss with the driving amount of the tilt mirror, or the actual angle and driving displacement of the tilt mirror can be solved by the intracavity loss to obtain a curve of the change of the actual angle and driving displacement with the driving amount of the tilt mirror.

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