Influence of radiation force of a high-energy laser beam on the second harmonic generation (SHG) efficiency through stress within a mounted potassium dihydrogen phosphate (KDP) crystal is studied, as well as an active method of improving the SHG efficiency by controlling the stress is proposed. At first, the model for studying the influence of the radiation force on the SHG efficiency is established, where the radiation force is theoretically analyzed, the stress caused by the radiation force is theoretically analyzed and numerically calculated using the finite-element method, and the influence of the stress on the SHG efficiency is theoretically analyzed. Then, a method of improving the SHG efficiency by controlling the stress through adjusting the structural parameters of the mounting set of the KDP crystal is examined. It demonstrates that the radiation force causes stress within the KDP crystal and further militates against the SHG efficiency; however, the SHG efficiency could be improved by controlling the stress through adjusting the structural parameters of the mounting set of the KDP crystal.
The wavefront distortion can directly influence on the optics quality of laser beam in ICF laser facility. The gravity is one of the major factors that cause the wavefront distortion. The back-support technology of the large aperture transport mirror has been developed to lessen the wavefront distortion caused by gravity. In the back-support technology, a joint structure between the mirror and the metal back-support has been developed. The requirement of joint is that the firm connection is realized with less wavefront distortion introduced. The adhesive structure and expanding mandrel structure have been analyzed and tested. The back-support of transport mirror in target area use the expanding mandrel for the reasons of the technics and fundamental frequency. The choice of material, the calculation force of clamp, the test of tensile, and the wavefront distortion analysis of transport mirror have been developed. The results show that the expanding mandrel can be used for the back-support of the large aperture transport mirror.
In ICF lasers, many independent laser beams are required to be positioned on target with a very high degree of accuracy during a shot. The target chamber provides a precision platform and datum reference for final optics assembly and target collimation and location system. The target chamber consists of shell with welded flanges, reinforced concrete pedestal, and lateral support structure. The field precision machining technology of target chamber in ICF lasers have been developed based on ShenGuangIII (SGIII). The same center of the target chamber is adopted in the process of design, fabrication, and alignment. The technologies of beam collimation and datum reference transformation are developed for the fabrication, positioning and adjustment of target chamber. A supporting and rotating mechanism and a special drilling machine are developed to bore the holes of ports. An adjustment mechanism is designed to accurately position the target chamber. In order to ensure the collimation requirements of the beam leading and focusing and the target positioning, custom-machined spacers are used to accurately correct the alignment error of the ports. Finally, this paper describes the chamber center, orientation, and centering alignment error measurements of SGIII. The measurements show the field precision machining of SGIII target chamber meet its design requirement. These information can be used on similar systems.
Operating posture of complicated opto-mechanical structures critically matter gravity-induced distortion of the structure, and further affect optical performance. With the aim to solve this problem, determination of operating postures of a supporting system of a KDP crystal is studied. A concept of key stiffness component is firstly proposed in this paper, as far as the authors are concerned, taking advantage of which gravity-induced distortion of the supporting system is analyzed, as well as the rotation of the KDP crystal that is cased by the distortion of the supporting system. Furthermore, effects of operating postures of the supporting system on the distortion of the supporting system and the rotation of the KDP crystal are investigated. It is demonstrated that key stiffness component is of great insignificance to distortion of the supporting system, and it could function as a guidance in determination of operating posture of the supporting system.
This paper presents the design of a 2 degree-of-freedom (DOF) rotation flexure mechanism (RFM) that could be utilized as the pivot for the mirror sub-assembly (MSA) of transport mirrors in the target area of inertial confinement fusion (ICF) laser systems. The hybrid spring system is established as the analytical model of the 2-DOF RFM. With the suitable matrix in coordinate transformation, the overall compliance matrix is developed to reveal the compliance property of the mechanism and the compliance equations are obtained. The analytical results obtained from the compliance equations are validated by means of finite element analysis (FEA) with the accuracy of 1%. The compliance property and design tradeoffs of the 2-DOF RFM are discussed with the compliance equations. The 2-DOF RFM for the MSA of transport mirrors of ShenGuangIII (SGIII) facility is designed and optimized. Then, the MSA is modeled and analyzed by FEA. The analysis result shows that the 2-DOF RFM is feasible for the MSA design.
Within Inertial Confinement Fusion (ICF) laser systems, many independent laser beams are required to be positioned on target with a very high degree of accuracy until shots are complete. Optical elements that are capable of moving a laser beam on the target must meet the pointing error budget. Optical elements are typically supported by systems which consist of mounts, mount frames, support structures, and foundation. The stability design for support systems in ICF laser have been developed based on the designing and evaluating experience of ShenGuangIII (SGIII). This paper will provide the methodology of position error budget. The stability allocation is developed for evaluating the performance of support systems when they are subjected to multiple sources of excitations that can cause the motion of optical elements during alignment procedures and before shots. The vibrational stability design considerations of support systems are discussed on the fundamental frequency, ambient random vibration, and modal damping. The support structures of optical elements are the relatively large and massive hybrid structure of reinforced concrete and steel frame or vessels. While the reinforced concrete portions provide optical elements stability, the steel portions afford design flexibility. Finite element analyses of ambient random vibration are typically performed to evaluate the vibrational stability performances of support systems. Finally, this paper describes the ambient random vibration and beam pointing error measurements of SGIII. The measurements show the support systems of SGIII meet design requirement. These information can be used on similar systems.