2. Institute of Optics and Electronics, Chinese Academy of Science, Chengdu, Sichuan 610209, China;
3. University of Chinese Academy of Sciences, Beijing 100049, China
Overview: The aberration in the inertial confinement fusion (ICF) system degrades the quality of high-power laser beam, bringing about problems such as decreasing of the laser focusing characteristic, blocking the plasma hole and decreasing of efficiency of the frequency tripling. The adaptive optics (AO) has been proved to be the key approach to solve the aberration problem in ICF, with its successful applications in the National Ignition Facility (NIF), OMEGA EP and Shen Guang I facility. This paper reports the fifty suites of engineered-manufacture adaptive optics systems developed for the Shen Guang Ⅲ (SGⅢ) facility.
The system structure of SGⅢ is briefly described first. Each AO system of SGⅢ consists of a high-accuracy-controll-ability and high-damage-threshold large aperture reflective dismountable deformable mirror and a Shack-Hartmann wavefront sensor. The deformable mirror is composed of 39 PZT actuators with dynamic range of ±5 μm. Its maximum and working apertures are 360 mm×360 mm and 320 mm×320 mm, respectively. The Shack-Hartmann wavefront sensor uses a micro-lens array of 22×22 with 484 efficient sub-apertures in the 6 mm×6 mm square aperture. Its dynamic range is more than 15 μm and its accuracy (RMS) is higher than 0.1 μm.
The deformable mirror is designed to meet the system requirement that PV and RMS of the residual wavefront are less than 1 μm and 0.2 μm, respectively, for the correction of the aberration of Zernike mode (±4 μm@1-10, ±1 μm@11-15). PV and RMS of the original surface and the dynamic range of the 50 suites of deformable mirrors are tested. The micro-deformation of the actuators after charging is also investigated.
The Shack-Hartmann wavefront sensor module consists of a Shack-Hartmann wavefront sensor, an electrical attenuator and a four-axis auto-align adjusting rack. The electrical attenuator adjusts the power of the incident laser beam to the working range of the Shack-Hartmann wavefront sensor. The four-axis auto-align adjusting rack aligns the Shack-Hartmann wavefront sensor to the incident laser beam. The dynamic range and the accuracy of the 50 suites of Shack-Hartmann wavefront sensor are tested.
In the end, the AO control scheme is also described in detail. All the sub-modules, including the deformable mirrors, Shack-Hartmann wavefront sensors and electrical switches, are connected and controlled via network. The C/S architecture is utilized and the control software can be deployed and run both locally and remotely. The characteristic of the static and dynamic aberration is analyzed and the correction strategy is illustrated. The result of system correction shows that the adaptive optics systems improved the beam quantity of the SGⅢ facility, meet the requirement that the laser beam energy is higher than 95% in the 10 time diffraction limit zone, and ensured the laser transmission in the main amplification system of the SGⅢ facility.