Preparation method and preparation device of high-stability laser thermal distortion correction window element based on alkaline earth fluoride

Abstract

The application relates to the field of high-power laser window element preparation devices and preparation methods, in particular to a preparation method and a preparation device of a high-stability laser thermal distortion correction window element based on an alkaline earth fluoride. In view of the problems of thermal distortion of output light spots and poor beam quality caused by temperature rise of window elements in a long-time running process of high-power lasers, the super-short and super-strong characteristics of an ultrashort pulse laser are utilized to realize non-thermal and high-quality laser welding processing on the surface of a light-transmitting element with a positive photo-thermal refractive index coefficient and an alkaline earth fluoride crystal element with a negative photo-thermal refractive index coefficient and similar absolute values of photo-thermal refractive index coefficients, so that the preparation of a laser thermal distortion correction window element with no thermal stress and high shear strength is realized.

Description

Technical Field

[0001] This invention relates to the field of high-power laser window element fabrication, and particularly to a method and apparatus for fabricating a high-stability laser thermal distortion correction window element based on alkaline earth fluorides. Background Technology

[0002] High-power laser technology plays an irreplaceable core supporting role in key fields such as advanced industrial manufacturing and aerospace. However, the operation of high-power lasers is accompanied by significant thermal effects, and current mainstream window elements (such as pure SiO2 glass materials like fused silica) all exhibit positive photothermal refractive index characteristics. This means that as high-power lasers are continuously output, the temperature of the window element gradually increases due to the absorption of laser energy (even weak absorption), and its refractive index changes significantly positively with the temperature increase, thus causing a shift in the beam transmission direction. More importantly, the non-uniform absorption and thermal conduction characteristics of laser energy within the element lead to a gradient temperature field distribution inside the element. This non-uniform temperature distribution induces severe thermal distortion effects, specifically manifested as element surface distortion, stress birefringence, and uneven refractive index distribution, ultimately significantly degrading the quality of the laser output beam (such as increased beam divergence angle and intensified wavefront distortion). In severe cases, it can even cause laser damage to the window element, restricting the stable operation and power improvement of high-power laser systems.

[0003] Currently, mainstream solutions for high-power laser thermal distortion correction largely rely on active material cooling technologies such as water cooling and air cooling. Their core principle is to passively suppress the degree of thermal distortion in the laser output field by artificially controlling the temperature field distribution of the components. However, these solutions face significant technical bottlenecks: on the one hand, the piping layout, temperature control precision, and sealing protection design of the cooling system all present significant engineering challenges; on the other hand, the insufficient dynamic response lag and uniformity of temperature regulation make it difficult to meet the stringent requirements of high-power laser systems in terms of thermal distortion correction accuracy. This greatly limits the large-scale application of high-power laser technology in a wider range of scenarios.

[0004] Crucially, in service scenarios such as aerospace, laser systems place extreme demands on the lightweighting, long-term operational stability, and high integration of core components. Traditional cooling solutions significantly increase system weight and volume due to additional structures, and complex piping designs can reduce the system's vibration and shock resistance, fundamentally contradicting the application requirements of this field. Therefore, there is an urgent need to develop a new technology for fabricating high-power laser window elements that combines high stability, high integration, and excellent thermal distortion self-correction performance. This technology enables active control of thermal distortion through the structural design and performance optimization of the element itself, rather than relying on external auxiliary systems. This not only overcomes the application limitations of traditional solutions but also provides core technological support for expanding the application scenarios and increasing the output power of high-power laser devices. Summary of the Invention

[0005] In view of this, the present invention provides a method and apparatus for preparing a highly stable laser thermal distortion correction window element based on alkaline earth fluorides. By utilizing the ultrashort and ultra-intense characteristics of ultrashort pulse lasers, a light-transmitting element with a positive photothermal refractive index coefficient is laser-welded with an alkaline earth fluoride material having a negative photothermal refractive index coefficient and similar absolute values ​​of the photothermal refractive index coefficients, thereby achieving the preparation of a highly stable laser thermal distortion correction window element.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the method for fabricating a highly stable laser thermal distortion correction window element based on alkaline earth fluorides according to the present invention includes the following steps: Step 1: Select a light-transmitting element with a positive optical thermal refractive index coefficient and an alkaline earth fluoride element with a negative optical thermal refractive index coefficient. The absolute value of the negative optical thermal refractive index coefficient of the alkaline earth fluoride element is similar to that of the positive optical thermal refractive index coefficient of the light-transmitting element. Perform advanced surface processing technology on the surfaces of the two elements to effectively remove the strong absorption defects on the surface and subsurface of the elements and optimize the microstructure and interface state of the element surface. Step 2: Then, the surfaces of the light-transmitting element and the alkaline earth fluoride element that have been treated with advanced surface processing technology in Step 1 are subjected to precision surface repair to ensure that the two elements can achieve high-precision tight bonding. Then, the two elements are subjected to ultrasonic cleaning and high-purity nitrogen purging in sequence to keep the bonding surfaces dry, clean and free of impurities. Step 3: Next, the light-transmitting element obtained in Step 2 is smoothly bonded to the surface to be bonded of the alkaline earth fluoride element, and the bonded stacked element is placed on the ultra-short pulse laser processing platform. By moving the axial height of the stacked element, the focusing point of the ultra-short pulse laser is moved to the bonding surface in the middle of the stacked element. Step 4: By adjusting the incident laser energy density, the light intensity is simultaneously made to reach the multiphoton absorption range of the materials of the light-transmitting element and the alkaline earth fluoride element. Through the nonlinear absorption effect, heatless and high-quality laser welding of the two elements is achieved.

[0007] This invention addresses the problems of thermal distortion and beam quality degradation in output beams caused by the temperature rise of window elements during long-term operation of high-power lasers. Utilizing the ultrashort and ultra-intense characteristics of ultrashort pulse lasers, it achieves heatless, high-quality laser welding on the surfaces of a transparent element with a positive optical-thermal refractive index and an alkaline earth fluoride crystal element with a negative optical-thermal refractive index and similar absolute values ​​of these coefficients. This enables the fabrication of laser thermal distortion correction window elements with no thermal stress and high shear strength. This invention not only solves the bottleneck problem of beam thermal distortion caused by heat accumulation in high-power laser systems but also yields a window component with high stability, adaptable to various application scenarios, and contributing to the expansion of applications for high-power laser devices.

[0008] In an optional embodiment, the advanced surface processing technology is any one of chemical mechanical polishing, ion beam etching, or magnetorheological polishing.

[0009] In an optional embodiment, the pulse width of the ultrashort pulse laser is less than 1 ns.

[0010] In optional embodiments, the alkaline earth fluoride element is a calcium fluoride element, a strontium fluoride element, a barium fluoride element, or a magnesium fluoride element; the light-transmitting element is a fused silica light-transmitting element or a glass light-transmitting element; preferably, the absolute difference between the photothermal refractive index coefficients of the light-transmitting element and the alkaline earth fluoride element is maintained at 2 × 10⁻⁶. -6 Within / K.

[0011] In an optional embodiment, the light-transmitting element is a fused silica light-transmitting element or a glass light-transmitting element.

[0012] In an optional implementation, the welding path and welding trace length are adjusted according to the actual size of the component and the light transmission aperture.

[0013] In an optional embodiment, the strong absorption defects include residual impurities, microcracks, and lattice distortions.

[0014] Secondly, the present invention provides an apparatus for fabricating a highly stable laser thermal distortion correction window element based on alkaline earth fluorides. The method for fabricating the highly stable laser thermal distortion correction window element based on alkaline earth fluorides is carried out using the apparatus for fabricating such an element.

[0015] In an optional embodiment, the fabrication apparatus for a high-stability laser thermal distortion correction window element based on alkaline earth fluorides includes an ultrashort pulse laser, a light source and optical path transmission unit, a beam monitoring unit, a welding execution unit, an auxiliary observation unit, and a general control system; wherein: An ultrashort pulse laser is fixedly installed at the left end of the device, and its output end emits pulsed laser in a horizontal direction. The light source and optical path transmission unit includes an attenuator, a first reflecting mirror, a second reflecting mirror, a third reflecting mirror, a focusing system, and a beam splitter. The pulsed laser output from the ultrashort pulse laser undergoes energy adjustment via the attenuator, and then sequentially passes through the first, second, and third reflecting mirrors to form a Z-shaped optical path, guiding the beam to the focusing system. The focusing system is used to converge the laser beam. A beam splitter is positioned directly below the focusing system and coaxial with the optical axis to perform beam splitting and sampling of the laser. The beam monitoring unit includes an energy meter and a beam quality analyzer; one beam after splitting enters the energy meter for real-time monitoring of laser energy; the other beam after splitting enters the beam quality analyzer for monitoring the spot shape and beam quality. The welding execution unit includes a stacked element and a three-dimensional displacement platform. A focused laser beam is vertically irradiated onto the stacked element, which is composed of an alkaline earth fluoride element with a negative photothermal refractive index and a light-transmitting element with a positive photothermal refractive index, with the focal point precisely located at the interface between the two elements. The stacked element is fixed on the three-dimensional displacement platform, and the precise positioning of the focal point on the bonding surface and the scanning of the welding path are achieved by the precise movement of the platform in the X, Y, and Z axes. An auxiliary observation unit, set coaxially or off-axis with the main optical path, is used for real-time imaging monitoring of the processing status and bonding interface morphology of the welding area. The overall control system is used for unified control and data acquisition of the device.

[0016] In an optional embodiment, the auxiliary observation unit is a CCD camera, which is located beside the stacked elements. Its optical axis forms a certain angle with the horizontal plane. Optionally, it is fixed on the optical platform by an adjustable angle bracket, and the center of the lens window is aligned with the height position of the mating surface of the two elements.

[0017] In an optional implementation, the computer acts as the central control system, establishing electrical / signal connections with the ultrashort pulse laser, the drive motor of the attenuator, the driver of the three-dimensional displacement platform, the energy meter, the beam quality analyzer, and the CCD camera via a data bus / communication interface, thereby forming a centralized monitoring and dispatching network.

[0018] In an optional embodiment, along the laser emission direction and coaxially arranged to the right of the ultrashort pulse laser are: an attenuator, whose optical axis is coaxial with the output optical axis of the ultrashort pulse laser; a first reflector, whose mirror normal forms a 45° angle with the incident optical axis, deflecting the horizontal incident beam upward by 90° and guiding it to a vertical direction; a second reflector, located directly above the first reflector, whose mirror normal forms a 45° angle with the incident optical axis, deflecting the vertical incident beam again by 90° and restoring it to a horizontal emission direction; and a third reflector. Located on the horizontal outgoing light path of the second reflecting mirror, its mirror normal forms a 45° angle with the incident optical axis, turning the horizontal beam downwards by 90° and guiding it to a vertically downward direction; directly below the third reflecting mirror and coaxially arranged along the vertical optical axis are: a focusing system, fixedly installed above the beam splitter; and a beam splitter, whose mirror normal forms a 45° angle with the vertical incident optical axis, positioned directly below the focusing system; the focusing system and the beam splitter are coaxial, and the focusing system converges the incident beam to its focal point.

[0019] In an optional implementation, along the reflected light path of the beam splitter, the following are arranged in sequence: an energy meter, located on the horizontal extension line of the beam splitter's reflected light output end, with its probe center coaxial and at the same height as the optical axis of the reflected beam; and a beam quality analyzer, located beside or at the rear optical path branch of the energy meter, with its probe plane perpendicular to the propagation direction of the received beam, and connected to the main control system via a USB / data cable.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Effectively improves the correction capability of laser thermal distortion. Compared with traditional artificial control technologies such as water cooling and air cooling, this invention can achieve real-time control of the thermal distortion effect of the optical field. That is, the two materials, the light-transmitting element and the alkaline earth fluoride element, have photothermal refractive index coefficients with similar absolute values ​​but opposite signs. This means that as the incident laser power increases, the photothermal refractive index coefficients of the two materials will change synchronously in real time, and the adjusted values ​​will remain consistent. This ensures real-time and effective correction of laser thermal distortion, avoiding the problems of slow response and poor control precision that exist in the artificial cooling control process.

[0021] 2. Improved component stability and integration. Compared to traditional optical component cooling systems, this invention reduces the need for complex systems such as water pipes and pumps, effectively reducing component size and increasing integration, thus facilitating applications in aerospace and other fields with extremely demanding component size requirements. Furthermore, this invention employs heatless laser welding technology using ultrashort pulse lasers, avoiding the introduction of thermal stress during component fabrication and improving component stability.

[0022] 3. High applicability. This invention can be used to fabricate high-power laser window elements of different sizes and functions. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a process flow diagram of the preparation method of the present invention.

[0025] Figure 2 This is a structural diagram of the preparation apparatus of the present invention.

[0026] Figure 3 This is a block diagram of the computer control principle of the present invention.

[0027] Figure 4 This is a laser welding morphology diagram of the fused silica element and the calcium fluoride crystal element in Embodiment 1 of the present invention.

[0028] Figure 5 This is a high-stability laser thermal distortion correction window element prepared from fused silica element and calcium fluoride crystal element according to Embodiment 1 of the present invention.

[0029] Figure 6 This is a test image of the effective correction of far-field spot distortion of the high-stability laser thermal distortion correction window element prepared by the fused silica element and calcium fluoride crystal element in Embodiment 1 of the present invention under 60W continuous laser irradiation.

[0030] Figure 7 This is a test image of far-field spot distortion when fused silica is used as a window element under 60W continuous laser irradiation.

[0031] The labels in the diagram represent the following: 1-Ultrashort pulse laser, 2-Attenuator, 3-First reflecting mirror, 4-Second reflecting mirror, 5-Third reflecting mirror, 6-Focusing system, 7-Beam splitter, 8-Energy meter, 9-Beam quality analyzer, 10-Alkali earth fluoride element with negative photothermal refractive index, 11-Transmitting element with positive photothermal refractive index, 12-CCD camera, 13-Three-dimensional displacement platform, 14-Computer, 15-Energy acquisition module, 16-Beam quality analyzer data acquisition module, 17-CCD camera data acquisition module, 18-Laser driver module, 19-Attenuator driver module, 20-Three-dimensional displacement platform driver module. Detailed Implementation

[0032] The present invention will be further illustrated by the following embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the present invention. The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] In the description of this invention, it should be understood that the terms "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. The invention will now be described in detail with reference to the accompanying drawings.

[0034] The fabrication principle of this invention is as follows: First, a light-transmitting element with a positive photothermal refractive index coefficient and an alkaline earth fluoride with a negative photothermal refractive index coefficient and similar absolute values ​​of these coefficients are selected as the unit elements for the laser thermal distortion correction window element. Through advanced surface processing technology, defects with strong laser absorption characteristics on the surfaces of the two unit elements are effectively removed, and surface shape repair is completed, ensuring a high degree of adhesion between the two element surfaces. Subsequently, through precise post-processing techniques such as ultrasonic cleaning and nitrogen purging, the two unit elements are effectively bonded. Then, by moving the ultrashort laser focus to the bonding surface of the two unit elements and adjusting the appropriate incident laser energy density, a heatless, high-quality laser welding of the two unit elements is achieved using the nonlinear absorption effect. The laser processing path and length are adjusted according to the element size and aperture requirements. The present invention relates to a method for fabricating a high-stability laser thermal distortion correction window element based on alkaline earth fluorides. This method involves heatless, high-quality laser welding of a light-transmitting element with a positive optical thermal refractive index coefficient and an alkaline earth fluoride element with a negative optical thermal refractive index coefficient. This process achieves the fabrication of a laser thermal distortion correction window element with high shear strength, thereby improving the beam quality of high-power laser output.

[0035] A light-transmitting element with a positive photothermal refractive index coefficient and an alkaline earth fluoride element with a negative photothermal refractive index coefficient and similar absolute values ​​of photothermal refractive index coefficients were selected. The surfaces of both elements were treated with advanced surface processing technology to effectively remove strong absorption defects (such as impurity residues, microcracks, lattice distortions, etc.) on the surface and subsurface of the two elements, and to optimize the microstructure and interface state of the element surface.

[0036] The thermo-optic coefficient (dn / dT) is the rate at which the refractive index (n) of a material changes with temperature (T). It quantitatively describes how much the refractive index of a material changes for every 1 degree Celsius (or 1 Kelvin) increase in temperature. A positive thermo-optic coefficient (dn / dT > 0) indicates that the refractive index of the material increases with increasing temperature. A negative thermo-optic coefficient (dn / dT < 0) indicates that the refractive index of the material decreases with increasing temperature.

[0037] The enhancing effect of electronic effects on materials with positive thermal refractive index is generally greater than the diluting effect of thermal expansion. Overall, as temperature increases, the speed of light slows down within the material, and the refractive index increases. Typical examples include most oxide optical glasses (such as quartz glass) and semiconductor materials (such as silicon and gallium arsenide).

[0038] In materials with negative photothermal refractive index coefficients, the dilution effect of thermal expansion is generally greater than the enhancing effect of electronic effects. As temperature increases, the density decrease due to increased interatomic spacing becomes the dominant factor, leading to a decrease in refractive index. Typical examples are ionic crystals, especially alkaline earth fluorides (such as calcium fluoride, barium fluoride, and magnesium fluoride).

[0039] In optional embodiments, the alkaline earth fluoride element includes, but is not limited to, any alkaline earth fluoride element such as calcium fluoride or strontium fluoride. In optional embodiments, the light-transmitting element includes, but is not limited to, any light-transmitting element such as fused silica or glass. Preferably, the absolute difference between the photothermal refractive index coefficients of the light-transmitting element and the alkaline earth fluoride element is maintained at 2 × 10⁻⁶. -6 Within / K. This can meet the requirements of the corrective element.

[0040] The advanced surface processing technology can be any of the following methods for processing component surfaces: chemical mechanical polishing, ion beam etching, magnetorheological polishing, etc. The purpose of this advanced surface processing technology is to ensure that both components can achieve uniform absorption of incident light intensity during subsequent laser processing. This advanced surface processing technology primarily targets the laser-processed surface of the components, i.e., the bonding surface.

[0041] Subsequently, the laser-processed surfaces of the two components underwent precision surface repair to ensure a high-precision, tight fit. Finally, the two components were sequentially ultrasonically cleaned and purged with high-purity nitrogen to ensure the surfaces to be bonded were dry, clean, and free of impurities, providing a reliable surface condition for subsequent bonding processes.

[0042] To achieve a high-precision, tight fit between two optical components (typically requiring a surface accuracy better than λ / 4), ultra-precision machining techniques are needed for surface correction. Methods for precision surface correction include, but are not limited to, ion beam shaping and magnetorheological polishing. Ion beam shaping involves bombarding the component surface with an ion beam in a vacuum environment to remove material layer by layer at the atomic level. Magnetorheological polishing utilizes a flexible polishing tool formed by a magnetorheological fluid under a magnetic field to controllably remove material from the component surface. In this invention, the surface roughness Ra of the component after precision surface correction is <0.5 nm.

[0043] The surfaces of the two components are smoothly bonded together, and the bonded stacked components are placed on an ultrashort pulse laser processing platform. By adjusting the axial height of the stacked components, the focusing point of the ultrashort pulse laser is moved to the bonding surface in the middle of the stacked components.

[0044] The ultrashort pulse laser can be a femtosecond, picosecond, or other ultrashort pulse laser with a pulse width of less than 1 ns. The ultrashort pulse laser is primarily selected from femtosecond (10⁻¹⁰) lasers. -15 s) and picosecond (10 -12 The s) scale range includes, but is not limited to: near-infrared femtosecond lasers with a center wavelength of approximately 800 nm, represented by Ti:sapphire; ytterbium-doped or erbium-doped fiber femtosecond lasers; and picosecond lasers based on mode-locked semiconductors or solid-state media.

[0045] By adjusting the incident laser energy density to ensure its intensity reaches the multiphoton absorption range of both materials, heatless, high-quality laser welding of the two components is achieved through nonlinear absorption effects. The welding path and welding trace length can be adjusted appropriately according to the actual size of the components and the aperture diameter.

[0046] The invention proposes a method for fabricating a high-stability laser thermal distortion correction window element based on alkaline earth fluorides. This method can effectively suppress the thermal distortion of the optical field caused by temperature rise under long-term irradiation by high-energy lasers, thereby improving the overall operational stability of the laser system. At the same time, it overcomes the problems of large equipment size and bulky structure caused by the reliance on passive cooling methods such as air cooling and water cooling of traditional window elements, providing technical support for the application expansion of high-energy laser devices in more working conditions.

[0047] Figure 2 This is a schematic diagram of the fabrication apparatus of the present invention. It includes an ultrashort pulse laser, a light source and optical path transmission unit, a beam monitoring unit, a welding execution unit, an auxiliary observation unit, and a general control system.

[0048] An ultrashort pulse laser 1 is fixedly installed at the left end of the device, and its output end emits pulsed laser in a horizontal direction.

[0049] The light source and optical path transmission unit includes an attenuator 2, a first reflector 3, a second reflector 4, a third reflector 5, a focusing system 6, and a beam splitter 7.

[0050] In the light source and optical path transmission unit, the pulsed laser output from the ultrashort pulse laser 1 undergoes energy adjustment via attenuator 2, and then its optical path is deflected by first reflector 3, second reflector 4, and third reflector 5, guiding the beam to focusing system 6. First reflector 3 deflects upwards, second reflector 4 deflects horizontally, and third reflector 5 deflects downwards, forming a Z-shaped optical path layout. The focusing system converges the laser beam to the middle bonding surface of the laminated element.

[0051] Along the laser emission direction, on the right side of the ultrashort pulse laser 1, are arranged coaxially (horizontally): an attenuator 2, whose optical axis is coaxial with the laser output optical axis; the attenuator 2 is electrically / signally connected to a computer control terminal via, for example, an electric rotation mechanism, for continuously adjusting the transmitted light intensity; a first reflecting mirror 3, whose mirror normal forms a 45° angle with the incident optical axis, deflecting the horizontal incident beam upward by 90° and guiding it to the vertical direction; and a second reflecting mirror 4, located directly above the first reflecting mirror 3, whose mirror normal forms a 45° angle with the incident optical axis, further deflecting the vertical incident beam by 90°. 0°, restoring the horizontal output direction; the third reflecting mirror 5, located on the horizontal output optical path of the second reflecting mirror 4, has its mirror normal at a 45° angle to the incident optical axis, deflecting the horizontal beam downwards by 90° and guiding it to a vertically downward direction; directly below the third reflecting mirror 5, along the vertical optical axis, are arranged coaxially in sequence: a focusing system 6, fixedly installed above the beam splitter 7; the beam splitter 7, with its mirror normal at a 45° angle to the vertical incident optical axis, is located directly below the focusing system 6; both have coaxial optical axes, and the focusing system converges the incident beam to its focal point. The beam splitter 7 can perform beam splitting and sampling of the incident laser. The beam splitter 7 proportionally divides the incident laser into a transmitted main beam (vertically downward) and a reflected sampling beam (entering the beam monitoring unit), thereby realizing non-contact real-time monitoring of the processed beam energy.

[0052] The beam monitoring unit includes an energy meter 8 and a beam quality analyzer 9. After beam splitting, one beam enters the energy meter 8 for real-time monitoring of laser energy; the other beam enters the beam quality analyzer 9 for monitoring the spot shape and beam quality. Specifically, along the reflected light path of the beam splitter 7, the following are arranged in sequence: the energy meter 8, located on the extension line of the reflected light exit end of the beam splitter 7, with its probe center coaxial and at the same height as the optical axis of the reflected beam; the energy meter 8 can be connected to a computer's data acquisition card via a signal cable; and the beam quality analyzer 9, located beside or at the rear optical path branch of the energy meter 8, with its probe plane perpendicular to the propagation direction of the received beam, and can be connected to a computer via USB / data cable.

[0053] The welding execution unit includes a stacked element and a three-dimensional displacement platform 13. A focused laser beam is vertically irradiated onto the stacked element, which is composed of an alkaline earth fluoride element 10 with a negative photothermal refractive index and a light-transmitting element 11 with a positive photothermal refractive index, tightly bonded together. The focal point is precisely located at the interface between the two elements. The stacked element is fixed on the three-dimensional displacement platform 13. Precise positioning of the focal point on the bonding surface and scanning of the welding path are achieved through precise movement of the platform in the X, Y, and Z axes. Specifically, directly below the focusing system 6, at its focal point, is a stacked element, consisting of an upper alkaline earth fluoride element 10 with a negative photothermal refractive index and a lower light-transmitting element 11 with a positive photothermal refractive index, tightly and vertically bonded together (the bonding surface of the two elements is horizontal and perpendicular to the optical axis of the focused laser beam, i.e., vertically incident). The geometric center of the bonded element is coaxially aligned with the optical axis of the focusing system 6. The stacked components are placed on the upper surface of the three-dimensional displacement platform 13. The alkaline earth fluoride component 10 with a negative photothermal refractive index and the light-transmitting component 11 with a positive photothermal refractive index can be fixed to the platform surface using vacuum adsorption or mechanical clamps to ensure no relative slippage during welding. The three-dimensional displacement platform 13 can be connected to a computer displacement control card via a multi-core control cable to achieve closed-loop motion control in the X, Y, and Z axes.

[0054] An auxiliary observation unit, such as a CCD camera 12, is used. The CCD camera 12 is coaxially or off-axis with the main optical path and is used for real-time imaging monitoring of the processing status and bonding interface morphology of the welding area. The CCD camera 12 is positioned beside the stacked components, with its optical axis forming a certain angle (e.g., 30°~45°) with the horizontal plane. It is fixed to the optical platform via an adjustable angle bracket, with the center of the lens window aligned with the height of the bonding surfaces of the two components. As an auxiliary observation unit, the CCD camera 12 requires an extremely stable observation environment. The optical platform refers to a precision vibration-isolated worktable used to build and support the optical experimental system. Fixing the CCD camera to the optical platform prevents camera shake when capturing microscopic images of the bonding interface, thus ensuring the clarity of the monitoring image and the accuracy of the data. The CCD camera 12 can be connected to a computer via an image acquisition card for real-time acquisition of microscopic images of the bonding interface.

[0055] The overall control system is, for example, computer 14. The operation of the entire overall control system is uniformly controlled and data acquired by computer 14. As the central control terminal, computer 14 establishes electrical / signal connections with the drive motors of the ultrashort pulse laser 1 and attenuator 2, the driver of the three-dimensional displacement platform 13, energy meter 8, beam quality analyzer 9, and CCD camera 12 through data bus / communication interface, forming a centralized monitoring and dispatching network.

[0056] Figure 3This is a block diagram of the computer control principle of the present invention. The computer 14, acting as the central control terminal, establishes bidirectional electrical connections with the ultrashort pulse laser 1, attenuator 2, three-dimensional displacement platform 13, energy meter 8, beam quality analyzer 9, and CCD camera 12 via a data bus and various communication interfaces, forming a centralized closed-loop monitoring and scheduling network for command issuance, execution feedback, and real-time monitoring. This includes a drive control link and a data acquisition and monitoring link.

[0057] The drive control link includes a laser drive module 18, an attenuator drive module 19, and a three-dimensional displacement platform drive module 20. The computer 14 sends control commands to each actuator via a data bus to achieve precise setting and real-time adjustment of processing parameters. The computer 14 establishes a connection with the ultrashort pulse laser 1 through the laser drive module 18, controlling parameters such as laser on / off, repetition frequency, pulse energy, and output power. This module supports real-time parameter readback to ensure the laser output state matches the preset values. The computer 14 establishes a connection with the drive motor of the attenuator 2 through the attenuator drive module 19, precisely adjusting the attenuator's transmittance by controlling the motor's rotation angle, thereby achieving continuous and fine control of the incident laser energy density. The computer 14 establishes a connection with the driver of the three-dimensional displacement platform 13 through the three-dimensional displacement platform drive module 20, controlling the platform's displacement, movement speed, and scanning path in the X, Y, and Z axes, achieving precise positioning of the laminated component bonding surfaces relative to the focal point and planning of the welding trajectory. All three drive modules have closed-loop feedback functionality. After the computer sends the target value, each module will transmit the actual status of the actuator (such as the actual rotation angle of the motor and the actual coordinates of the platform) back to the computer in real time for the system to perform deviation correction.

[0058] The data acquisition and monitoring link includes an energy acquisition module 15, a beam quality analyzer data acquisition module 16, and a CCD camera data acquisition module 17. Each monitoring element uploads the acquired signals to the computer 14 via its corresponding data acquisition module, providing data for real-time control of the processing. The energy acquisition module 15 connects to the energy meter 8, acquiring the single-pulse energy or average power data of the incident laser in real time and transmitting it to the computer 14. The computer compares the measured values ​​with a set threshold; if the energy fluctuation exceeds the allowable range, it automatically triggers the attenuator drive module 19 for dynamic compensation adjustment. The beam quality analyzer data acquisition module 16 connects to the beam quality analyzer 9, transmitting the beam diameter, beam ellipticity, and M... 2 Parameters such as the laser beam quality factor and beam pointing stability are collected in real time and transmitted back to the computer 14 to monitor whether the laser beam quality meets the welding process requirements. The CCD camera data acquisition module 17 is connected to the CCD camera 12 and transmits the real-time microscopic image of the bonding interface to the computer 14 for operators or image recognition algorithms to locate the welding area, judge the focus status, and evaluate the welding quality online.

[0059] Based on the aforementioned hardware connections, the control software embedded in the computer 14 implements the following collaborative logic: During the startup phase, the computer 14 activates the ultrashort pulse laser 1 via the laser driver module 18, simultaneously adjusts the attenuator 2 to the initial safe energy level via the attenuator driver module 19, and moves the stacked components to the initial processing position via the three-dimensional displacement platform driver module 20 through the three-dimensional displacement platform 13; During the welding phase, the computer 14 sends displacement commands to the three-dimensional displacement platform driver module 20 in real time according to the preset welding path, while continuously monitoring the incident laser state via the energy acquisition module 15 and the beam quality analyzer data acquisition module 16 to ensure that the energy density at the focal point remains stable within the multiphoton absorption threshold range of the two materials; During the monitoring phase, the CCD camera data acquisition module 17 continuously acquires images of the bonding interface and uploads them to the computer 14. The computer, combined with image processing algorithms, determines in real time whether the welding trajectory has deviated or whether defects have occurred on the bonding surface, and automatically pauses processing and issues an alarm signal if necessary.

[0060] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the appropriate range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below.

[0061] This embodiment proposes a method for fabricating a highly stable laser thermal distortion correction window element based on alkaline earth fluorides, comprising the following steps: Step 1, select a material with a positive thermal refractive index coefficient (9.6 × 10⁻⁶). -6 A circular fused silica element with a diameter of 35 mm and a thickness of 10.00 mm ( / K) and a negative photothermal refractive index coefficient, and an absolute value of the photothermal refractive index coefficient close to that of -10.6 × 10⁻⁶. -6 Circular calcium fluoride crystal elements (6K), each 30 mm in diameter and 11.04 mm thick, were subjected to advanced surface ion beam etching to a depth of 20 μm. This effectively removed defects with strong absorption characteristics in the subsubstrate of both elements and optimized the surface microstructure and interface state, ensuring uniform absorption of the incident laser at the contact surface during subsequent femtosecond pulsed laser welding. Precision surface repair was then performed on the laser-processed surfaces of both elements to ensure a high-precision, tight fit. The surface accuracy of the fused silica element and the calcium fluoride crystal element is approximately λ / 4. The surface roughness Ra of both elements is approximately 0.5 nm.

[0062] Step 2 involves ultrasonically cleaning the two components and purging them with 99.999% pure nitrogen gas to ensure that the surfaces of the calcium fluoride crystal and the fused silica remain dry, clean, and free of impurities, thus providing a reliable surface condition for the subsequent bonding process.

[0063] Step 3: Smoothly bond the surfaces of the two calcium fluoride crystals and the fused silica, and place the bonded stacked element on a femtosecond pulsed laser (pulse width of 200 fs) processing platform. By moving the axial height of the stacked element, the focusing point of the femtosecond pulsed laser is moved to the bonding surface between the calcium fluoride crystal and the fused silica element, with a spot diameter of 20 μm.

[0064] Step 4: Adjust the incident laser intensity to 10 GW / cm 2 This allows the light intensity to simultaneously reach the multiphoton absorption range of both fused silica and calcium fluoride crystal materials. Through nonlinear absorption effects, heatless, high-quality laser welding of the two components is achieved. The welding path is fabricated using a grid with an interval of 0.01 mm. Figure 4 The processing area is centered on the center of the calcium fluoride crystal, and the welding diameter is 25mm. Laser welding is performed to achieve a stable weld between fused silica and calcium fluoride crystal.

[0065] Figure 5 This is a high-stability laser thermal distortion correction window element prepared from fused silica element and calcium fluoride crystal element according to Embodiment 1 of the present invention.

[0066] Through shear stress testing, the shear strength of the high-stability laser thermal distortion correction window element based on alkaline earth fluoride described in this invention can reach 10.241 MPa, demonstrating high stability.

[0067] Figure 6 This image shows a test result of the high-stability laser thermal distortion correction window element, fabricated from fused silica and calcium fluoride crystal elements according to Embodiment 1 of this invention, under 60W continuous laser irradiation, demonstrating effective correction of far-field spot distortion. The light field energy distribution test results show that the alkaline earth fluoride / fused silica composite welded high-stability laser thermal distortion correction window proposed in this invention maintains a uniform Gaussian energy distribution in the far-field spot under 60W continuous pulse laser irradiation. Furthermore, by tuning the positive and negative photothermal refractive index coefficients and thickness of the fused silica and calcium fluoride crystals during high-energy laser irradiation, the temperature of both elements is consistently controlled within ±1℃, thereby achieving effective correction of laser thermal distortion by the high-stability optical window element.

[0068] Figure 7This is a test image of far-field beam distortion under 60W continuous laser irradiation, using fused silica as the window element. In contrast, the pure fused silica window element exhibits significant degradation and uneven distortion in its far-field beam energy distribution due to laser thermal distortion. The comparative results demonstrate that the composite window structure of this invention can effectively suppress beam thermal distortion and achieve high-quality thermal distortion correction. Similarly, using only calcium fluoride as the window element also fails to achieve high-quality thermal distortion correction.

[0069] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for fabricating a highly stable laser thermal distortion correction window element based on alkaline earth fluorides, characterized in that, The preparation method includes the following steps: Step 1: Select a light-transmitting element with a positive optical thermal refractive index coefficient and an alkaline earth fluoride element with a negative optical thermal refractive index coefficient. The absolute value of the negative optical thermal refractive index coefficient of the alkaline earth fluoride element is similar to that of the positive optical thermal refractive index coefficient of the light-transmitting element. Perform advanced surface processing technology on the surfaces of the two elements to effectively remove the strong absorption defects on the surface and subsurface of the elements and optimize the microstructure and interface state of the element surface. Step 2: Then, the surfaces of the light-transmitting element and the alkaline earth fluoride element that have been treated with advanced surface processing technology in Step 1 are subjected to precision surface repair to ensure that the two elements can achieve high-precision tight bonding. Then, the two elements are subjected to ultrasonic cleaning and high-purity nitrogen purging in sequence to keep the surfaces to be bonded dry, clean and free of impurities. Step 3: Next, the light-transmitting element obtained in Step 2 is smoothly bonded to the surface to be bonded of the alkaline earth fluoride element, and the resulting stacked element is placed on the ultra-short pulse laser processing platform. By moving the axial height of the stacked element, the focusing point of the ultra-short pulse laser is moved to the bonding surface in the middle of the stacked element. Step 4: By adjusting the intensity of the incident laser, the light intensity is simultaneously made to reach the multiphoton absorption range of the materials of the light-transmitting element and the alkaline earth fluoride element. Through the nonlinear absorption effect, heatless and high-quality laser welding of the two elements is achieved.

2. The preparation method according to claim 1, characterized in that, The advanced surface processing technology can be any one of chemical mechanical polishing, ion beam etching, or magnetorheological polishing.

3. The preparation method according to claim 1, characterized in that, The pulse width of the ultrashort pulse laser is less than 1 ns; the ultrashort pulse laser is selected from femtosecond ultrashort pulse lasers and picosecond ultrashort pulse lasers.

4. The preparation method according to claim 1, characterized in that, The alkaline earth fluoride element is a calcium fluoride element, a strontium fluoride element, a barium fluoride element, or a magnesium fluoride element; the light-transmitting element is a fused silica light-transmitting element or a glass light-transmitting element; the absolute difference between the photothermal refractive index coefficients of the light-transmitting element and the alkaline earth fluoride element is maintained at 2 × 10⁻⁶. -6 Within / K.

5. The preparation method according to claim 1, characterized in that, The incident laser intensity in step 4 is 8~10 GW / cm². 2 .

6. A fabrication apparatus for a high-stability laser thermal distortion correction window element based on alkaline earth fluorides, characterized in that, The method for fabricating a high-stability laser thermal distortion correction window element based on alkaline earth fluorides according to any one of claims 1 to 5 is carried out using an apparatus for fabricating a high-stability laser thermal distortion correction window element based on alkaline earth fluorides.

7. The apparatus for fabricating a high-stability laser thermal distortion correction window element based on alkaline earth fluorides according to claim 6, characterized in that, The fabrication apparatus for a high-stability laser thermal distortion correction window element based on alkaline earth fluorides includes an ultrashort pulse laser, a light source and optical path transmission unit, a beam monitoring unit, a welding execution unit, an auxiliary observation unit, and a general control system; wherein: An ultrashort pulse laser (1) is fixedly installed at the left end of the device, and its output end emits pulsed laser in the horizontal direction; The light source and optical path transmission unit includes an attenuator (2), a first reflector (3), a second reflector (4), a third reflector (5), a focusing system (6), and a beam splitter (7). The pulsed laser output from the ultrashort pulse laser (1) is regulated by the attenuator (2), and then passes through the first reflector (3), the second reflector (4), and the third reflector (5) in sequence to form a Z-shaped optical path, and guides the beam to the focusing system (6). The focusing system (6) is used to converge the laser beam. A beam splitter (7) is provided directly below the focusing system (6) and at a position coaxial with the optical axis for laser beam splitting and sampling. The beam monitoring unit includes an energy meter (8) and a beam quality analyzer (9); one beam after splitting enters the energy meter (8) for real-time monitoring of laser energy; the other beam after splitting enters the beam quality analyzer (9) for monitoring the spot shape and beam quality. The welding execution unit includes a stacked element and a three-dimensional displacement platform (13). The focused laser beam is vertically irradiated onto the stacked element, which is composed of an alkaline earth fluoride element (10) with a negative photothermal refractive index coefficient and a light-transmitting element (11) with a positive photothermal refractive index coefficient. The focal point is precisely located at the bonding interface of the two elements. The stacked element is fixed on the three-dimensional displacement platform (13). The precise positioning of the focal point on the bonding surface and the scanning of the welding path are achieved by the precise movement of the platform in the X, Y, and Z axes. An auxiliary observation unit, set coaxially or off-axis with the main optical path, is used for real-time imaging monitoring of the processing status and bonding interface morphology of the welding area. The overall control system is used for unified control and data acquisition of the device.

8. The apparatus for fabricating a high-stability laser thermal distortion correction window element based on alkaline earth fluorides according to claim 7, characterized in that, The auxiliary observation unit is a CCD camera (12), which is set on the side of the stacked element. Its optical axis is at a certain angle to the horizontal plane. It can be optionally fixed on the optical platform by an adjustable angle bracket, and the center of the lens window is aligned with the height position of the mating surface of the two elements.

9. The apparatus for fabricating a high-stability laser thermal distortion correction window element based on alkaline earth fluorides according to claim 7, characterized in that, The computer (14) serves as the overall control system. It establishes electrical / signal connections with the drive motors of the ultrashort pulse laser (1), attenuator (2), driver of the three-dimensional displacement platform (13), energy meter (8), beam quality analyzer (9), and auxiliary observation unit through the data bus / communication interface, forming a centralized monitoring and scheduling network.

10. The apparatus for fabricating a high-stability laser thermal distortion correction window element based on alkaline earth fluorides according to claim 7, characterized in that, Along the laser emission direction, on the right side of the ultrashort pulse laser (1) are arranged the following coaxially: attenuator (2), whose optical axis is coaxial with the output optical axis of the ultrashort pulse laser (1); The first reflector (3) has a mirror normal at a 45° angle to the incident optical axis, which deflects the horizontal incident beam upward by 90° and guides it to the vertical direction; the second reflector (4) is located directly above the first reflector (3), with its mirror normal at a 45° angle to the incident optical axis, which deflects the vertical incident beam upward by 90° and restores it to the horizontal direction; the third reflector (5) is located on the horizontal outgoing optical path of the second reflector (4), with its mirror normal at a 45° angle to the incident optical axis, which deflects the horizontal beam downward by 90° and guides it to the vertical downward direction; directly below the third reflector (5) and along the vertical optical axis, the following are arranged coaxially: a focusing system (6), which is fixedly installed directly above the beam splitter (7); the beam splitter (7) has its mirror normal at a 45° angle to the vertical incident optical axis and is located directly below the focusing system (6); the focusing system and the beam splitter are coaxial, and the focusing system converges the incident beam to its focal point.

11. The apparatus for fabricating a high-stability laser thermal distortion correction window element based on alkaline earth fluorides according to claim 7, characterized in that, In the direction of the reflected light path of the beam splitter (7), the following are arranged in sequence: an energy meter (8), located on the extension line of the reflected light output end of the beam splitter (7), with its probe center coaxial with the optical axis of the reflected beam at the same height; and a beam quality analyzer (9), located on the side or rear optical path branch of the energy meter (8), with its probe plane perpendicular to the propagation direction of the received beam, and connected to the main control system via a USB / data cable.

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