A method for measuring the execution accuracy of a tilt mirror based on an intracavity loss model

Abstract

The present invention provides a method for measuring the execution accuracy of a tilt mirror based on an intracavity loss model. First, the tilt mirror to be measured is used as one of the cavity mirrors to build an optical cavity ring-down system. Next, a drive is applied to the tilt mirror to generate an expected angular tilt. According to the intracavity loss model of the optical cavity ring-down system, the actual angular tilt amount executed by the tilt mirror can be obtained. The execution accuracy of the tilt mirror can be calculated based on the deviation between the actual executed angular tilt amount and the expected amount. This method utilizes the characteristic that the intracavity loss of the ring-down cavity is extremely sensitive to the tilt angle of the cavity mirror, and has high sensitivity in measuring the execution accuracy of the tilt mirror, and can be used as an effective means for testing the related performance of the tilt mirror.

Description

Technical Field

[0001] The present invention relates to the field of laser technology, and particularly to a method for measuring the execution accuracy of a tilt mirror based on an intracavity loss model, which can be applied to fields such as adaptive optics and optical axis control. Background Art

[0002] The tilt mirror can generate angular tilt amounts in the horizontal and vertical directions to achieve the control of the optical axis direction of the incident light beam. The tilt mirror is one of the key devices in the field of beam control technology, and its own performance has an important impact on the accuracy and stability of beam control. The execution accuracy of the tilt mirror is one of the important technical indicators of the tilt mirror. If there is a deviation in the execution accuracy of the tilt mirror, it will bring feedback errors to the beam control system, affecting the control accuracy and control efficiency.

[0003] In recent years, in order to improve the execution accuracy of the tilt mirror, a series of methods have been developed successively (Chinese Patent CN110927920A, "A Fast Tilt Mirror Position and Rate Control Device and Method Based on a Grating Scale"; Chinese Patent CN103809651A, "Piezoelectric Tilt Mirror Drive Power Supply System"). However, in terms of the measurement of the execution accuracy, there is currently a lack of high-precision technical means. The current main measurement means all rely on the spot positioning of the detection beam (Chinese Patent CN110530612A, "A System for Testing a Tilt Mirror Using a PSD and Its Testing Method"; Chinese Patent CN104215431A, "A Performance Testing Device for a Fast Tilt Mirror"). In practical applications, the measurement accuracy of the above means will be limited by the pixel size of the area array detector or the system complexity.

[0004] In view of this, the present invention utilizes the characteristic that the intracavity loss of the ring-down cavity is extremely sensitive to the misalignment angle of the cavity mirror. The tilt mirror is incorporated into the optical cavity ring-down system as one of the cavity mirrors. The tilt mirror angle execution amount is used as the cavity mirror angle misalignment amount. According to the intracavity loss model, the error between the actual angle execution amount and the expected execution amount of the tilt mirror can be obtained with high precision, and the two-dimensional distribution of the execution error in the horizontal and vertical directions can be obtained. This method can improve the measurement accuracy of the tilt mirror execution accuracy and is of great significance to the field of beam control technology. Summary of the Invention

[0005] The technical problem to be solved by the present invention is that the current measurement means for the execution accuracy of the tilt mirror all rely on spot positioning, and the positioning accuracy is limited by the pixel size of the area array detector and the complexity of the optical system.

[0006] The technical solution adopted by the present invention to solve its technical problems is as follows: By taking advantage of the fact that the intracavity loss of the ring-down cavity is extremely sensitive to the misalignment angle of the cavity mirror, an optical cavity ring-down system is built with the tilted mirror as the cavity mirror, so as to convert the tilt angle execution amount of the tilted mirror into the cavity mirror misalignment amount. According to the intracavity loss model, the error between the actual tilt angle execution amount and the expected execution amount of the tilted mirror can be obtained with high precision.

[0007] The technical solution adopted by the present invention is: A method for measuring the execution accuracy of a tilted mirror based on an intracavity loss model, and the specific implementation steps are as follows:

[0008] Step (1), Build an optical cavity ring-down system, including a narrow-linewidth continuous-wave laser, a plane cavity mirror, a plano-concave cavity mirror, a photodetector, a tilted mirror to be measured, and a processor, etc., a total of 6 parts. Among them, for the narrow-linewidth continuous-wave laser, the output laser linewidth should not be greater than 1 nm, and the output wavelength λ thereof and the reflectivity R of the tilted mirror at this wavelength λ should satisfy R λ ≥ 98%;

[0009] Step (2), Establish the intracavity loss model M of this optical cavity ring-down system. This intracavity loss model is the relationship between the intracavity loss factor δ and the tilt angle α of the tilted mirror, which can be described as δ = M(α x,y ), and the subscripts represent the horizontal direction and the vertical direction respectively. The establishment method of the intracavity loss model can adopt three methods: theoretical calculation, system simulation, and experimental measurement.

[0010] Step (3), Inject a narrow-linewidth continuous-wave light beam into the ring-down cavity, and at the same time use a photodetector to monitor and record the intracavity transmission signal in real time. Apply a tilt angle amount α to the tilted mirror, and at the same time calculate the actually executed angle amount θ at this time according to the intracavity loss model M. The difference between α and θ is the execution accuracy of this tilted mirror.

[0011] The tilt angle amount α can be a single value in the horizontal direction (denoted as the x direction), the vertical direction (denoted as the y direction), or a two-dimensional distribution in these two directions.

[0012] The principle of the present invention is: The intracavity loss of the ring-down cavity is extremely sensitive to the misalignment angle of the cavity mirror. According to the intracavity loss model, the misalignment angle of the cavity mirror corresponding to the cavity loss factor can be obtained with high precision.

[0013] Compared with the prior art, the present invention has the following advantages: This method has the characteristics of simple structure, convenient operation, and efficient measurement. At the same time, this method has extremely high theoretical accuracy and high sensitivity. It can provide a highly sensitive means for detecting the relevant technical indicators of the tilted mirror and is a useful supplement in this technical field. Description of the Drawings

[0014] Figure 1Schematic diagram of a device for a method of measuring the execution accuracy of a tilting mirror based on an intracavity loss model according to the present invention; where 1 is a narrow-linewidth continuous-wave laser, 2 is a plane cavity mirror, 3 is a plano-concave cavity mirror, 4 is a photodetector, 5 is the tilting mirror to be measured, and 6 is a processor.

[0015] Figure 2 Example diagram of the intracavity loss model of a method for measuring the execution accuracy of a tilting mirror based on an intracavity loss model according to the present invention.

[0016] Figure 3 Example diagram of an embodiment of a method for measuring the execution accuracy of a tilting mirror based on an intracavity loss model according to the present invention. Specific implementation manner

[0017] The following combines the attached Figure 1 And specific implementation manners to further illustrate the present invention.

[0018] As Figure 1 shown, a method for measuring the execution accuracy of a tilting mirror based on an intracavity loss model according to the present invention is specifically implemented as follows:

[0019] Step (1), Build an optical cavity ring-down system, including six parts: a narrow-linewidth continuous-wave laser 1, a plane cavity mirror 2, a plano-concave cavity mirror 3, a photodetector 4, the tilting mirror 5 to be measured, and a processor 6. The plane cavity mirror 2, the plano-concave cavity mirror 3, and the tilting mirror 5 to be measured together form a folded ring-down cavity. The narrow-linewidth continuous-wave laser 1 emits a laser beam, which is coupled into the ring-down cavity by the plane cavity mirror 2. The optical intensity signal of the ring-down cavity is transmitted by the plano-concave cavity mirror 3, and the transmitted optical intensity enters the photodetector 4. The ring-down cavity transmission signal detected by the photodetector is processed by the processor 6.

[0020] In this embodiment, the narrow-linewidth continuous-wave laser 1 is a continuous-wave laser with a central wavelength of 1064 nm and a linewidth of 0.5 nm. The tilting mirror 5 to be measured is a high-speed piezoelectric tilting mirror, with a reflectivity above 99.9% in the 1064 nm band and a designed stroke of ±0.01°.

[0021] Step (2), Establish an intracavity loss model δ = M(α x,y );

[0022] In this embodiment, the intracavity loss model is established by theoretical calculation. According to parameters such as the reflectivity of the plane cavity mirror 2, the reflectivity of the plano-concave cavity mirror 3, the radius of curvature, and the reflectivity of the tilting mirror 5 to be measured, a theoretical model of the optical cavity ring-down system is established. Then, a two-dimensional angle scan α x,y is applied to the tilting mirror 5 to be measured in the theoretical model. The scan range is ±0.01°, and the two-dimensional distribution diagram of the cavity loss factor and the angle obtained is as shown in the attached Figure 2 figure.

[0023] Step (3): Inject a narrow linewidth continuous wave beam into the optical cavity, and simultaneously use a photodetector 4 to monitor and record the intracavity transmission signal in real time. Apply an inclination angle α to the tilt mirror 5 to be measured, and simultaneously calculate the actually executed angle θ at this time according to the intracavity loss model M. The difference between α and θ is the execution accuracy of the tilt mirror.

[0024] In this embodiment, keep the tilt mirror tilted at -0.01° in the x direction, and apply a series of inclination angles to the tilt mirror 5 to be measured. Among them, at the position where α = -0.009°, record the cavity transmission signal, and calculate the intracavity loss factor δ according to the transmission signal α ≈990 ppm. According to δ α Combined with the intracavity loss M, it can be known by looking up the table that at the position where α = -0.009°, the theoretical cavity loss factor should be approximately 990.8 ppm, and the angle coordinate θ corresponding to 990 ppm is approximately -0.0095°. Based on this, the difference between α and θ can be calculated to be approximately 0.0005°. This embodiment shows that the actual execution error of the tilt mirror to be measured is approximately 0.0005° at -0.01° in the x direction and -0.009° in the y direction. Further two-dimensional scanning can obtain the two-dimensional distribution of the execution accuracy of the tilt mirror. This implementation process can also be expressed as: f(α - θ) = δ α -M(α).

[0025] The content not described in detail in the specification of the present invention belongs to the prior art well-known to those skilled in the art.

Claims

1. A method for measuring the execution accuracy of a tilt mirror based on an intracavity loss model, characterized in that The implementation steps are as follows: Step (1): Build an optical cavity ring-down system, including a narrow-linewidth continuous-wave laser (1), a plane mirror (2), a plano-concave mirror (3), a photodetector (4), a tilt mirror to be measured (5), and a processor (6); among them, the plane mirror (2), the plano-concave mirror (3), and the tilt mirror to be measured (5) form a folded ring-down cavity. The narrow-linewidth continuous-wave laser (1) emits a laser beam, which is coupled into the ring-down cavity by the plane mirror (2). The optical intensity signal in the ring-down cavity is transmitted through the plano-concave mirror (3) and enters the photodetector (4). The ring-down cavity transmission signal detected by the photodetector is processed by the processor (6); Step (2): Establish the intracavity loss model of the optical cavity ring-down system M ; The intracavity loss model M is the relationship between the intracavity loss factor δ and the tilt angle of the tilt mirror α , which can be described as δ = M ( α x,y ), where the subscripts of the angles α represent the horizontal and vertical directions respectively; The establishment method of the intracavity loss model can adopt three methods: theoretical calculation, system simulation and experimental measurement Step (3): Inject a narrow linewidth continuous wave beam into the ring-down cavity, and simultaneously use a photodetector to monitor and record the intracavity transmission signal in real time, and apply an inclination angle to the tilt mirror α , and simultaneously according to the intracavity loss model M calculate the actually executed angle at this time θ , α The difference between θ and α is the execution accuracy of the tilt mirror; where the inclination angle α is a single value with the horizontal direction denoted as the x direction and the vertical direction denoted as the y direction, or a two-dimensional distribution in both directions.

2. The method for measuring the execution accuracy of a tilt mirror based on a cavity loss model according to claim 1, wherein: For the narrow-linewidth continuous-wave laser described in step (1), the output laser linewidth should be no greater than 1 nm.

3. A method for measuring the execution accuracy of a tilt mirror based on an intracavity loss model according to claim 1, characterized in that: The narrow linewidth continuous wave laser described in step (1), whose output wavelength λ and the reflectivity of the tilt mirror at this wavelength R λ should satisfy R λ ≥ 98%.

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