Single-actuator focal length controllable anamorphic lens assembly and thermal lens compensation method

Abstract

The application relates to the technical field of lasers, and provides a single-actuator focal length controllable variable mirror assembly and a thermal lens compensation method.The single-actuator focal length controllable variable mirror assembly comprises a mirror surface support with a base; a variable mirror with a gradually changing structure of a middle thick edge thin structure, the variable mirror being fixed to the mirror surface support; a single piezoelectric actuator arranged between the center of the variable mirror and the mirror surface support, the piezoelectric actuator changing in length by an external electric signal, so that the variable mirror is deformed, thereby adjusting and controlling the radius of curvature R of the variable mirror; a high-voltage amplifier electrically connected to the piezoelectric actuator and used for applying voltage to the piezoelectric actuator; and a controller used for outputting a control instruction to the high-voltage amplifier, the high-voltage amplifier applying a calculated driver control voltage to the piezoelectric actuator, so that the radius of curvature R of the variable mirror reaches a target value. The single-actuator focal length controllable variable mirror assembly is used for realizing thermal lens compensation of a laser.

Description

Technical Field

[0001] This application relates to the field of laser technology, and more specifically to a single-actuator focal length controllable deformable mirror assembly and a method for thermal lens compensation. Background Technology

[0002] During laser operation, after the laser medium absorbs the pump light energy, most of the energy is converted into heat and deposited inside the laser working medium, causing a temperature rise. Under continuous pumping and heat conduction, a significant temperature gradient forms inside the working medium, transforming it from a homogeneous refractive index medium into a lens-like medium—leading to beam focusing when it passes through, a phenomenon known as thermal self-focusing or thermal lensing. Thermal lensing not only rapidly increases the laser beam divergence angle and degrades beam quality, but in severe cases, it can also create solid focal points within the working medium, causing laser damage to the material. As lasers develop towards higher power and higher repetition rates, thermal lensing has become a key bottleneck limiting the improvement of laser output power and beam quality.

[0003] To suppress or compensate for the thermal lensing effect, various technical solutions have been proposed in the industry. One common approach is to process the end face of the laser gain medium into a concave surface for compensation. However, this method can only compensate for the thermal lensing effect under specific pump power, and the precision machining of the concave crystal significantly increases the manufacturing cost. Another commonly used method is to design a resonant cavity based on the concept of a thermally stable fundamental mode cavity, so that the fundamental mode parameters remain constant or change very slowly within a certain pump power range. However, this method usually requires the laser medium to be as close as possible to the output coupling mirror end and the cavity length to be much greater than the crystal length. Therefore, it is only suitable for applications with a small range of pump power variation. Once the pump power changes significantly, the thermally stable cavity structure will be broken, and the far-field divergence angle and beam width of the output light will change significantly.

[0004] To achieve thermal lensing compensation over a wider power range, researchers have attempted to introduce external compensation devices. For example, a movable compensation lens driven by a stepper motor is placed between the solid-state laser medium and the output mirror. By adjusting the position of the compensation lens, the thermal lens and the compensation lens form a Keplerian telescope, thus compensating for the thermal lensing effect. However, this method has significant limitations: when the focal length of the thermal lens is large (e.g., several meters), the sum of the focal lengths of the thermal lens and the compensation lens is quite large, making it difficult to arrange in practical laser devices; furthermore, inserting additional optical elements into the resonant cavity increases laser loss and reduces output efficiency. Another approach uses an electrically tunable liquid lens as the compensation lens, adjusting the voltage to change the refractive power of the liquid lens to adapt to changes in the thermal lens, but the response speed, long-term stability, and ability to withstand high-power lasers of the liquid lens still need to be verified.

[0005] It is evident that existing thermal lens compensation technologies generally suffer from problems such as limited compensation range, insufficient dynamic response, and complex structure, making it difficult to simultaneously meet the needs of high-power lasers for large-range, high-efficiency, and low-loss thermal lens compensation. Summary of the Invention

[0006] To address the above problems, this application proposes a single-actuator focal length controllable deformable mirror assembly and a method for thermal lens compensation. The specific solution is as follows: According to a specific embodiment of this application, this application provides a single-actuator focal length controllable deformable mirror assembly for laser thermal lens compensation, comprising: Mirror-finished stand with base; The deformable mirror has a gradient structure that is thicker in the middle and thinner at the edges, and the deformable mirror is fixed to the mirror support. A single piezoelectric actuator is positioned between the center of the deformable mirror and the mirror support. An external electrical signal alters the extension / retraction length of the piezoelectric actuator, causing the deformable mirror to deform and thus controlling its radius of curvature R. The radius of curvature R of the deformable mirror satisfies the following relationship: ; in, It is a constant related to the structure of the piezoelectric actuator. The control voltage for the external electrical signal, Young's modulus of the deformable mirror material; Poisson's ratio is the material of the deformable mirror. This is the scaling factor for the deformable mirror thickness; A high-voltage amplifier, electrically connected to the piezoelectric actuator, is used to apply voltage to the piezoelectric actuator; The controller is used to output control commands to the high-voltage amplifier, and the high-voltage amplifier applies the calculated driver control voltage to the piezoelectric actuator so that the radius of curvature R of the deformable mirror reaches the target value.

[0007] In some embodiments, it also includes: An actuator drive board is disposed between the base and the piezoelectric actuator, and is used to convert the control signal into a drive signal for the piezoelectric actuator to achieve precise control of the piezoelectric actuator.

[0008] In some embodiments, it also includes: A mirror-shaped annular clamp is disposed at the end of the mirror support opposite to the base, and is used to fix the edge of the deformable mirror. When the piezoelectric actuator extends or retracts, the edge of the deformable mirror is subjected to a uniform reaction force.

[0009] In some embodiments, the material of the deformable mirror includes at least one of the following: glass, copper, silicon, quartz, and molybdenum.

[0010] In some embodiments, the piezoelectric actuator is formed of a piezoelectric ceramic material.

[0011] In some embodiments, the thickness t of the deformable mirror varies with the radius r according to the following relationship: ; Where D(r) is the stiffness of the deformable mirror.

[0012] This application also provides a method for thermal lens compensation based on a single-actuator focal length controllable deformable mirror assembly as described in any of the above claims, comprising: The spherical wavefront distortion caused by the uneven heating of the pump light in the disk crystal is periodically detected by a wavefront sensor. Based on the spherical wavefront distortion, calculate the target surface shape with the same curvature but opposite sign as the spherical wavefront distortion. Calculate the control voltage for controlling the radius of curvature of the deformable mirror based on the target surface shape; The controller outputs control commands to apply the control voltage to the single piezoelectric actuator to change the curvature of the deformable mirror, causing it to deform into a surface shape conjugate with the spherical wavefront distortion for thermal lens compensation.

[0013] In some embodiments, the controller outputs control commands, including: The controller periodically outputs control commands.

[0014] In some embodiments, the controller outputs control commands, including: When the control voltage is within a preset range, the controller outputs a control command.

[0015] In some embodiments, the controller outputs control commands, including: When the time interval between the current moment and the last time a control command was output is greater than a preset threshold, a control command is output through the controller.

[0016] Compared with the prior art, the above-described solutions of this application have at least the following beneficial effects: This application designs a gradually thickened deformable mirror surface based on elasticity theory, employing a single actuator vertical drive method to induce a centrally symmetric spherical deformation. Precise control of the piezoelectric actuator allows for the generation of a suitable spherical surface within the dynamic range of the deformable mirror, meeting the thermal lens compensation requirements of the disk laser. Simultaneously, a high-reflectivity film of the appropriate wavelength is deposited on the deformable mirror surface to meet the high reflectivity requirements of the disk laser at its operating wavelength, reducing optical loss and ensuring stable laser operation. This application achieves precise focal length control of the spherical deformable mirror using a single actuator, simplifying the overall design of the deformable mirror system and effectively reducing system development and application costs.

[0017] This application uses a controller to output control commands to a high-voltage amplifier. The high-voltage amplifier then applies the calculated driver control voltage to the corresponding actuator of the deformable mirror. Since the actuator and the gradient thickness deformable mirror are fixedly connected by optical adhesive, the focal length of the deformable mirror is made to reach the design value through precise control of the actuator voltage, ultimately achieving the goal of controllable spherical focal length of the deformable mirror. Laser thermal lensing compensation is achieved through a single-actuator focal length controllable deformable mirror assembly. Attached Figure Description

[0018] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application. It is obvious that the drawings described below are merely some embodiments of this application, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort. In the drawings: Figure 1 This is a structural diagram of a single-actuator focal length controllable deformable mirror assembly according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the dynamic adjustment of a single-actuator focal length controllable deformable mirror assembly according to an embodiment of the present invention; Figure 3 This is a flowchart illustrating a method for thermal lens compensation in a single-actuator focal length controllable deformable mirror assembly according to an embodiment of the present invention.

[0019] Explanation of reference numerals in the attached drawings: 1. High-reflectivity film; 2. Deformable mirror; 3. Piezoelectric actuator; 4. Actuator drive plate; 5. Base; 6. Mirror ring clamp; 7. Mirror support; 8. High voltage amplifier; 9. Controller. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0021] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a product or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a product or device. Without further limitation, an element defined by the phrase "comprising one" does not exclude the presence of other identical elements in the product or device that includes that element.

[0022] Deformable mirrors are core components in adaptive optics, correcting aberrations in the optical path by altering their mirror surface morphology. In disk lasers, the gain medium is affected by thermal effects after pump light incident, causing spherical distortion in the disk crystal. This distortion, in turn, is influenced by the pump light power. This application utilizes a focal length-controllable deformable mirror to compensate for this distortion. Deformable mirrors can be categorized by their driving method, including piezoelectric deformable mirrors, thermodynamic deformable mirrors, and pneumatic deformable mirrors. Piezoelectrically driven deformable mirrors offer advantages such as fast response speed and stable performance.

[0023] In related technologies, mirror deformation is achieved through multi-actuator piezoelectric deformable mirrors. However, multi-actuator piezoelectric deformable mirrors typically require a large number of actuators to ensure the mirror fitting effect. As the number of actuator channels increases, the mechanical coupling effect between units in multi-actuator piezoelectric deformable mirrors significantly increases, which can easily lead to significant deformation crosstalk. The introduction of a large number of actuators also leads to problems such as high hardware cost, large size, and significantly increased wiring and integration difficulty in the drive control system.

[0024] This application designs the thickness of the deformable mirror's reflector surface and employs a single-actuator piezoelectric drive to induce a centrally symmetrical spherical deformation in the deformable mirror. By precisely controlling the voltage of the piezoelectric ceramic, the radius of curvature of the mirror surface can be continuously adjusted, thereby achieving precise control of the focal length of the spherical deformable mirror.

[0025] The embodiments of this application are described in detail below with reference to the accompanying drawings.

[0026] like Figure 1 , Figure 2 As shown, this application provides a single-actuator focal length controllable deformable mirror assembly for laser thermal lens compensation, comprising: a mirror support 7 with a base 5; a deformable mirror 2 having a gradient structure that is thicker in the middle and thinner at the edges, the deformable mirror 2 being fixed to the mirror support 7; and a single piezoelectric actuator 3 disposed between the center of the deformable mirror 2 and the mirror support 7, wherein the extension and retraction length of the piezoelectric actuator 3 is changed by an external electrical signal to deform the deformable mirror 2, thereby controlling the radius of curvature R of the deformable mirror 2, the radius of curvature R of the deformable mirror 2 satisfying the following relationship: ; in, It is a constant related to the structure of the piezoelectric actuator. The control voltage for the external electrical signal, Young's modulus of the deformable mirror material; Poisson's ratio is the material of the deformable mirror. This is the scaling factor for the deformable mirror thickness; A high-voltage amplifier 8 is electrically connected to the piezoelectric actuator 3 and is used to apply voltage to the piezoelectric actuator 3; a controller 9 is used to output control commands to the high-voltage amplifier 8, and the high-voltage amplifier 8 applies the calculated driver control voltage to the piezoelectric actuator 3 so that the radius of curvature R of the deformable mirror 2 reaches the target value.

[0027] This application designs the surface of a gradually thickened deformable mirror 2 based on elasticity theory. The deformable mirror 2 is a circular plate mirror, and its optical shape is mainly obtained by bending the circular plate. This mirror surface is planar in a static state without external force. Based on thin-plate theory, the deformation of the deformable mirror is adjusted to form a spherical mirror as follows: ; in, It is the deformation variable of the deformable mirror. Let be the radius of curvature of the deformable mirror. The deformable mirror is the radius of the deformable mirror. The gradually thickening active deformable mirror is an axisymmetric circular mirror. Let the thickness of the deformable mirror vary with the radius of the deformable mirror as a function. Then the thickness The relationship with material properties is as follows: ; In the formula: For stiffness; Young's modulus of the material; The material's Poisson's ratio.

[0028] According to elasticity theory, the relationship between the torque, stiffness, and deformation inside a material in cylindrical coordinates is as follows: ; ; ; in, Radial bending moment; Tangential bending moment; Radial torque; This is the tangential torque.

[0029] Radial and tangential bending moments , With the shear force acting on the flat plate element The static equilibrium between them is obtained from the local tangential axis and is expressed as: ; By applying a central axial force This causes an edge reaction force. This yields the base deformation. If it is equivalent to a uniform surface load... Let the radius of the deformable lens be 'a', and define the central force. Deformation is produced by applying a force at the center of the lens and a reaction force at the edge, and the following relationship exists: Therefore: ; Substitution Seeking ; Bring it in The thickness distribution is obtained by solving. , This is the scaling factor for the deformable mirror thickness. The overall scaling ratio that determines the thickness of the entire lens is a fixed design value that does not change with the radius. and The expression is as follows: , ; The radius of curvature R of the deformable mirror satisfies: ; According to the principle of piezoelectric actuators, the upward force of the single actuator at the center of the deformable mirror is: ; in, It is the force acting on a single piezoelectric actuator. It is the voltage applied by the piezoelectric actuator. This is a constant related to the structure of the piezoelectric actuator. The spherical radius of curvature of the deformable mirror can be adjusted by the actuator driving voltage to achieve precise curvature control. The radius of curvature of the deformable mirror with a single actuator... The expression is as follows: ; In practical applications, the thickness is usually a finite value. The cutoff criterion at the center thickness is the Rayleigh quarter-wavelength criterion; the axial force is not applied at a single point, but rather over a small region, typically with a radius of... .

[0030] In some embodiments, an actuator drive board 4 is further included, disposed between the base 5 and the piezoelectric actuator 3, for converting the control signal into a drive signal for the piezoelectric actuator 3, thereby achieving precise control of the piezoelectric actuator 3. The actuator drive board 4 is an electronic interface module connecting the control system and the piezoelectric actuator 3. Its function is to convert the control signal into the drive signal required by the actuator and achieve precise control.

[0031] In some embodiments, the device further includes: a mirror annular clamp 6, disposed at the end of the mirror support 7 opposite to the base 5, for fixing the edge of the deformable mirror 2, so that when the piezoelectric actuator 3 extends or retracts, the edge of the deformable mirror 2 is subjected to a uniform reaction force.

[0032] In some embodiments, the material of the deformable mirror 2 includes at least one of the following: glass, copper, silicon, quartz, and molybdenum.

[0033] In some embodiments, the piezoelectric actuator 3 is formed of a piezoelectric ceramic material.

[0034] In some embodiments, a high-reflectivity film 1 of a corresponding wavelength is deposited on the upper surface of the deformable mirror 2 to reflect most of the light of a specific wavelength.

[0035] In some embodiments, the thickness t of the deformable mirror 2 varies with the radius r according to the following relationship: ; Where D(r) is the stiffness of the deformable mirror.

[0036] like Figure 3 As shown, this application also provides a method for thermal lens compensation according to the single-actuator focal length controllable deformable mirror assembly described in any of the above claims, comprising the following steps: Step S102: Periodically detect the spherical wavefront distortion caused by the uneven heating of the pump light in the disk crystal by using a wavefront sensor; Step S104: Calculate the target surface shape with the same curvature but opposite sign as the spherical wavefront distortion, based on the spherical wavefront distortion. Step S106: Calculate the control voltage for controlling the radius of curvature of the deformable mirror based on the target surface shape; Step S108: The controller outputs a control command to apply the control voltage to the single piezoelectric actuator to change the curvature of the deformable mirror, so that it deforms into a surface shape conjugate with the spherical wavefront distortion for thermal lens compensation.

[0037] In some embodiments, outputting control commands through the controller includes periodically outputting control commands through the controller. In this application, the compensation for the thermal lensing effect of the disc crystal is periodic, by periodically adjusting the curvature of the deformable mirror by controlling the control voltage of a single piezoelectric actuator based on the detection results, so that it deforms into a surface shape conjugate to the spherical wavefront distortion for thermal lensing compensation. This enables automatic real-time compensation of the thermal lensing effect to improve beam quality.

[0038] In some embodiments, outputting control commands through the controller includes: outputting control commands through the controller when the control voltage is within a preset range. In this embodiment, it is necessary to determine whether the control voltage is within the preset range. If the voltage change is too small, the actual compensation effect is not obvious, so there is no need to output control commands to avoid frequent adjustments that could damage the single-actuator focal length controllable deformable mirror assembly. If the voltage change is too large, exceeding the upper limit of the preset range, it may be due to an error in detection or calculation. In this case, there is also no need to output adjustment voltage; an alarm signal can be given for manual inspection. The specific preset range can be set according to experiments and is not limited thereto.

[0039] In some embodiments, outputting control commands through the controller includes: outputting a control command through the controller when the time interval between the current moment and the last time a control command was output is greater than a preset threshold. In this embodiment, a time threshold can be set to avoid frequent output of control voltage causing damage to the single-actuator focal length controllable deformable mirror assembly. That is, if the time interval is less than the time threshold, even if the voltage change is large, no drive control voltage will be output. Only when the time interval is greater than the time threshold will a control signal be output to achieve scientific control.

[0040] In some embodiments, a dual-verification control can be performed by combining a time threshold and a voltage threshold. The control command is only output when both the time threshold and the voltage threshold are satisfied. For example, the control command is only output when the time is greater than the time threshold and the voltage is within a preset range, so as to achieve more precise control.

[0041] This application designs a gradually thickened deformable mirror surface based on elasticity theory, employing a single actuator vertical drive method to induce a centrally symmetric spherical deformation. Precise control of the piezoelectric actuator allows for the generation of a suitable spherical surface within the dynamic range of the deformable mirror, meeting the thermal lens compensation requirements of the disk laser. Simultaneously, a high-reflectivity film of the appropriate wavelength is deposited on the deformable mirror surface to meet the high reflectivity requirements of the disk laser at its operating wavelength, reducing optical loss and ensuring stable laser operation. This application achieves precise focal length control of the spherical deformable mirror using a single actuator, simplifying the overall design of the deformable mirror system and effectively reducing system development and application costs.

[0042] This application uses a controller to output control commands to a high-voltage amplifier. The high-voltage amplifier then applies the calculated driver control voltage to the corresponding actuator of the deformable mirror. Since the actuator and the gradient thickness deformable mirror are fixedly connected by optical adhesive, the focal length of the deformable mirror is made to reach the design value through precise control of the actuator voltage, ultimately achieving the goal of controllable spherical focal length of the deformable mirror. Laser thermal lensing compensation is achieved through a single-actuator focal length controllable deformable mirror assembly.

[0043] Finally, it should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the systems or apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple, and relevant parts can be referred to the method section.

[0044] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A single-actuator focal length controllable deformable mirror assembly, used for thermal lens compensation in lasers, characterized in that, include: The mirror support (7) has a base (5); The deformable mirror (2) has a gradient structure that is thick in the middle and thin at the edges, and the deformable mirror (2) is fixed to the mirror support (7). A single piezoelectric actuator (3) is positioned between the center of the deformable mirror (2) and the mirror support (7). By applying an external electrical signal, the extension and retraction length of the piezoelectric actuator (3) is changed, causing the deformable mirror (2) to deform, thereby controlling the radius of curvature R of the deformable mirror (2). The radius of curvature R of the deformable mirror (2) satisfies the following relationship: ； in, It is a constant related to the structure of the piezoelectric actuator. The control voltage for the external electrical signal, Young's modulus of the deformable mirror material; Poisson's ratio is the material of the deformable mirror. This is the scaling factor for the deformable mirror thickness; A high-voltage amplifier (8) is electrically connected to the piezoelectric actuator (3) and is used to apply voltage to the piezoelectric actuator (3); The controller (9) is used to output control commands to the high voltage amplifier (8), and the high voltage amplifier (8) applies the calculated driver control voltage to the piezoelectric actuator (3) so that the radius of curvature R of the deformable mirror (2) reaches the target value.

2. The single-actuator focal length controllable deformable mirror assembly according to claim 1, characterized in that, Also includes: An actuator drive plate (4) is disposed between the base (5) and the piezoelectric actuator (3) to convert the control signal into a drive signal for the piezoelectric actuator (3) so as to achieve precise control of the piezoelectric actuator (3).

3. The single-actuator focal length controllable deformable mirror assembly according to claim 1, characterized in that, Also includes: A mirror ring clamp (6) is provided at the end of the mirror support (7) opposite to the base (5) to fix the edge of the deformable mirror (2). When the piezoelectric actuator (3) extends or retracts, the edge of the deformable mirror (2) is subjected to a uniform reaction force.

4. The single-actuator focal length controllable deformable mirror assembly according to claim 1, characterized in that, The material of the deformable mirror (2) includes at least one of the following: glass, copper, silicon, quartz, and molybdenum.

5. The single-actuator focal length controllable deformable mirror assembly according to claim 1, characterized in that, The piezoelectric actuator (3) is formed of piezoelectric ceramic material.

6. The single-actuator focal length controllable deformable mirror assembly according to claim 1, characterized in that, The thickness t of the deformable mirror (2) varies with the radius r according to the following relationship: ； Where D(r) is the stiffness of the deformable mirror.

7. A method for thermal lens compensation of a single-actuator focal length controllable deformable mirror assembly according to any one of claims 1-6, characterized in that, include: The spherical wavefront distortion caused by the uneven heating of the pump light in the disk crystal is periodically detected by a wavefront sensor. Based on the spherical wavefront distortion, calculate the target surface shape with the same curvature but opposite sign as the spherical wavefront distortion. Calculate the control voltage for controlling the radius of curvature of the deformable mirror based on the target surface shape; The controller outputs control commands to apply the control voltage to the single piezoelectric actuator to change the curvature of the deformable mirror, causing it to deform into a surface shape conjugate with the spherical wavefront distortion for thermal lens compensation.

8. The method according to claim 7, characterized in that, The controller outputs control commands, including: The controller periodically outputs control commands.

9. The method according to claim 7, characterized in that, The controller outputs control commands, including: When the control voltage is within a preset range, the controller outputs a control command.

10. The method according to claim 7, characterized in that, The controller outputs control commands, including: When the time interval between the current moment and the last time a control command was output is greater than a preset threshold, a control command is output through the controller.

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