Improvement of fundamental frequency performance of SGII-UP laser facility

Abstract

The SGⅡ-UP laser facility is one of the most important high power laser systems in China and one of the few inertial confinement fusion laser devices in the world that operate all year round. In order to further improve its output capacity to meet higher physical requirements, measures such as increasing the number of neodymium glasses, adopting new N41 neodymium glasses, and improving the energy configuration of xenon lamps are taken to improve the gain capacity of the main amplifier. Calculation of the new main amplifier construction model predicts the small gain coefficient will reach 4.9%. And further modulation of the laser device shows a reduction of injection energy from 5J to 1.26J when a 10kJ fundamental frequency energy output is demanded, which supports a higher output energy as well as a stronger commission ability. Furthermore, B integral is analyzed with a result of a obvious reduction under different laser pulses injection conditions of 1ns, 5ns, 10ns, which means a better near-filed quality of the beams. Accordingly small-size modulation suppression of induced by non-linear phase shift while high fluence laser passing is expected before and after the improvement, which is a key prerequisite to a higher commission energy. Based on these analyses, fundamental frequency output energies with different pulse injections are calculated and an improvement from 8kJ to 12.5kJ commission is expected under 10ns square pulse condition. Tests show that the small signal gain coefficient of the device increases from 4.15%/cm to 4.94%/cm, consistent with simulation results and the mean gain multiple of a single beam increases from 9000 to 118000 with more than an order of magnitude. Commission verifies the fundamental frequency output capacity exceeding 12.5kJ under 10ns square pulse as well as a small-size modulation suppression around 0.16mm<sup>-1</sup> as a result of joint action of non-linear phase shift and spatial filtering. After the significant improvement, the SGⅡ-UP laser facility will strongly support more ambitious physical experiment targets.