The problem of laser induced damage of optical materials is one bottleneck to restrict laser power levels and beam quality enhances unceasingly. The research on laser induced optical material damage, improving optical material laser damage threshold, becomes a hot issue in the development of laser technology. In this paper, laser-induced sapphire damage morphology using nanosecond 1064nm Nd: YAG is reported. Analyzed the temperature variation of sapphire inclusion under different laser fluence irradiation, and the temperature variation of inclusion's dimension radius by finite element method. The laser-induced damage experiment of sapphire materials are investigated (pulse width is 6ns). At the same time, the sapphire laser-induced damage threshold, the damage position distribution, the influence of different laser fluence on the damage area and damage growth characteristics are analyzed. Results show that the inclusion absorption mechanisms can better explain the sapphire under the nanosecond laser pulse irradiation damage, and simulation results are in agreement with the experimental results. In addition, for 1-on-l irradiation, the surface damage area for sapphire surface increase linearly, for s-on-1 irradiation, the damage area on the back surface increases exponentials with the increase of shot number.
The coherent addition of multiple beams is one of the great challenges in terms of large-scale lasers. Implementing the capability to generate ultra-high-focus power intensity on the focal plane places stringent requirements on the control of each beam’s pointing and intra-beam phasing. The random beam-to-beam phase jumps, mainly induced by the catoptric elements’ rapid vibration, should be eliminated to realize phase locking. A two-way laser beam’s coherent combination test bed is designed to test the capabilities of phase-locking system. The results show that the closed-loop feedback system achieved a high contrast of the in-phase intensity pattern at the receiving plane after correcting for piston and tip/tilt errors between two adjacent laser beams by the stochastic parallel gradient descent algorithm.