Aiming to minimize the surface distortion of large-aperture laser transport mirrors in high-power laser facilities, an assembly design and mounting method are proposed for the mirror. First, a theoretical model on the mirror surface deformation is established. With a new assembly design, the mirror is fastened on its neutral plane and its optical surface distortion can be precisely compensated through several adjustable forces on the sides, which will generate bending moments on the mirror body. Furthermore, a dynamic kinematic joint is designed, in which a corresponding relationship between spring compression and screw rotation ensures the accurate control of the magnitude of mirror preload. Finally, the performance of the presented method has been validated through field experiments and numerical simulations. This transport mirror assembly and mounting design have obvious technical advantages on simple mechanical structure, high operational efficiency, and precise preload control. The results show that the assembly design and optimized mounting strategy can keep the total surface distortion of the mirror within 350 nm (peak-valley).
Large aperture KDP crystals are mainly used in the final optic assembly of inertial confinement fusion facility to change the frequency of laser light incident into them. For the optimization of the surface of large aperture KDP crystals, this paper proposes an assembly scheme based on point support and calculates the surface state of KDP crystal under different installation postures and different preload force distributions and magnitudes by numerical simulation. The results show that the assembly scheme can effectively reduce the surface distortion of KDP crystal after assembly. For example, in the horizontal state, the surface PV value of the KDP crystal can be controlled below 5um and the frequency conversion efficiency can reach 83.7% after assembly.
In huge-scale high peak power laser facility, the frequency conversion unit is responsible for the conversion of fundamental infrared wave at 1053nm into ultraviolet wave at 351nm. In this paper, the mechanism of service performance degradation of frequency doubling crystal is revealed by combining field experiments and numerical simulations. Moreover, we propose a flexure support method that can effectively reduce crystal surface distortion. Further, an experiment platform for offline mounting of frequency conversion crystal is built, and the mechanical and optical characteristics are verified by the experimental results. Finally, online verification is carried out in China’s high peak power laser facility. The results show that the proposed mounting method can significantly modify the crystal surface figure, improve its online performance and increase the highest efficient output power of high peak power laser facility.
The contamination on optical surface is an important factor that causes laser-induced damage. In the assembly process of the SGIII, the traditional manual assembly method poses a great challenge in terms of the cleanliness of optical components. So the contamination introduced by the manual assembly is studied including particulate and non-volatile residue (NVR). The use of vacuum system device to clamp is an important means to achieve automated clean assembly. The contact contamination is the main source of contaminants in the vacuum-clamping process. One source is the organic residue left on the optical surface, by comparing the residue of different sealing rubber after absorbing the optics, we find that FPM (fluorine rubber) brings the least contamination. The second source is the coating debris causing by the compressive and shear stress on the optical surface during the vacuum clamping process. We have established a theoretical model, through the numerical simulation method to obtain the stress under different assembly conditions. For different optical films, the stress during the assembly process cannot exceed the fatigue limit of the optical coating to prevent the film from being destroyed and debris contamination. The cleanliness level of the vacuum clamp assembly process is evaluated through experiments. The results show that the contamination generated by assembling large-aperture optics with a vacuum gripper meets the optical surface cleanliness requirements.
KEYWORDS: Crystals, Distortion, Frequency converters, Metals, Laser crystals, Process modeling, Second-harmonic generation, National Ignition Facility, Data conversion, Differential equations
KDP frequency converters are the important components applied in the final optics assembly for Inertial Confinement Fusion device. And the efficiency of second harmonic generation is much affected by phase matching error, which is induced by surface distortion. In this paper, focusing on the surface distortion under the specific mounting process of KDP frequency converters, we proposed an effective prediction method based on modified mechanical model to accurately predict the surface distortion during assembly. Using numerical simulation, we analyze the key elements that influence the surface distortion so as to adjust the mounting process according to the results. Results and findings in this article are meaningful for improving mounting-induced surface distortion of KDP frequency converters. Moreover, the mechanical model and prediction method presented will offer more efficient and reliable technical proposal for next generation ICF facility
In high-power laser system, the surface wavefront of large optics has a close link with its structure design and mounting method. The back-support transport mirror design is presently being investigated as a means in China’s high-power laser system to hold the optical component firmly while minimizing the distortion of its reflecting surface. We have proposed a comprehensive analytical framework integrated numerical modeling and precise metrology for the mirror’s mounting performance evaluation while treating the surface distortion as a key decision variable. The combination of numerical simulation and field tests demonstrates that the comprehensive analytical framework provides a detailed and accurate approach to evaluate the performance of the transport mirror. It is also verified that the back-support transport mirror is effectively compatible with state-of-the-art optical quality specifications. This study will pave the way for future research to solidify the design of back-support large laser optics in China’s next generation inertial confinement fusion facility.
Surface control and phase matching of large laser conversion optics are urgent requirements and huge challenges in high-power solid-state laser facilities. A self-adaptive, nanocompensating mounting configuration of a large aperture potassium dihydrogen phosphate (KDP) frequency doubler is proposed based on a lever-type surface correction mechanism. A mechanical, numerical, and optical model is developed and employed to evaluate comprehensive performance of this mounting method. The results validate the method’s advantages of surface adjustment and phase matching improvement. In addition, the optimal value of the modulation force is figured out through a series of simulations and calculations.
This paper puts forward an adaptive optics (AO) mounting method of large aperture KDP frequency doubler used in high power solid state lasers. Integrated optomechanical theory is proposed and applied to verify the mechanical and optical performances of this AO method particularly. According to the thin plate theory and nonlinear optics theory, optomechanical model is developed. Then, the finite element method is employed to establish the numerical model and simulate the distortion process of the crystal plates under various boundary conditions. The results indicate that this AO method could correct the deformed surface and modify the phase matching condition significantly, which means the second harmonic generation (SHG) efficiency will be improved as well.
Motivated by the demand to minimize the mount-induced wavefront aberration of the large-aperture laser transport mirror, a low-stress flexure mounting configuration is proposed. Specific optomechanical analyses, including theoretical modeling, numerical analysis and field experiment, are presented. The mechanical properties of the flexure support were studied specifically. Besides, the relation between the mounting forces and the root-mean-square of the gradients (GRMS) value of the mirror surface is studied. Then, the appropriate value of the bolt preload is set to 500N, with which the GRMS value is just 5.35 nm/cm. The results indicate that the flexure mounting configuration is indeed a feasible and promising method to solve the mount-induced distortion problem of large-aperture optics.
In high-power solid-state laser facility (SG-III), focusing laser beams into the target center with precision better than 50 microns (RMS) is dependent on the stringent specifications of thousands of large-aperture transport mirror units and is a huge challenge on the surface aberration control of mirrors. The current mirror’s mounting techniques with screw fastening loads has several engineering conundrums – low control precision for loads (higher scatter even~±30%), and low assembly-rectification efficiency (~100 screws). To improve the current screw-fastening method, a new-style flexure supports method, which has a wonderful performance on uniform control of the external loads and only uses ~30 screws, is proposed to mount the mirror (size: 610mm×440mm×85mm). With theoretical modeling and FEM analysis, the impacts of mounting loads on mirror’s surface aberrations are analyzed and discussed in detail, and the flexure supports system is designed. Finally, with experimental research and case studies, the proposed flexure supports method shows a powerful performance on even control precision of external loads with scatter even less than ±10%, which is a promising mounting process to replace the threaded fasteners mounting the large-aperture optics. These improvements can lay a foundation for mounting process consistency, robustness, and assembly-rectification efficiency of large optical component.
TM1-6S1 large aperture laser transport mirror is a crucial optical unit of high power solid-state laser in the Inertial Confinement Fusion (ICF) facility. This article focuses on the low-stress and precise mounting method of large-aperture mirror. Based on the engineering practice of SG-III, the state-of-the-art and key problems of current mounting configuration are clarified firstly. Subsequently, a brand new low-stress mounting configuration with flexure supports is proposed. Opto-mechanical model of the mirror under mounting force is built up with elastic mechanics theory. Further, numerical methods and field tests are employed to verify the favorable load uniform capacity and load adjust capacity of flexure supports. With FEM, the relation between the mounting force from new configuration and the mirror surface distortion (wavefront error) is clarified. The novel mounting method of large aperture optics could be not only used on this laser transport mirror, but also on the other transmission optics and large crystals in ICF facilities.
In the high-power laser facility (SG-III), focusing 48 laser beams into the target center better than 50 microns (RMS) within a few picoseconds is dependent on the stringent specifications of thousands of large optics and also puts huge challenges on the engineering characteristics of the design and mounting. A parametric optomechanical method is proposed to evaluate the performance of a 400 mm large-aperture transport mirror. With theoretical modeling and numerical analysis, the impacts of assembly structure, manufacturing errors, mounting loads, and gravity on the mirror surface aberrations are calculated and discussed in detail. With field experiments and case studies, the proposed method shows a powerful performance on the mirror surface aberrations’ evaluation, and negative impacts of currently used mounting techniques for the mirror are found. Finally, a new assembly design is presented based on a discussion of its advantages.
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