Wavelength stabilization of high power laser systems using volume holographic gratings

Abstract

We present our latest experimental results in wavelength stabilization of high power laser diode systems by using Volume Holographic (Bragg) Gratings. Such systems are used as optical pumps to increase the efficiency and brightness of Thin Disk Lasers. To achieve a wide locking range from threshold until maximum operation current (for example from 30A to 250A), careful control of laser system alignment is necessary to ensure effective feedback and locking, without using strong gratings which could reduce laser efficiency. For this purpose, we use wavefront correction optics to compensate for laser bar smile and Fast Axis Collimation pointing errors. We reduce the pointing errors from ~ 1 mrad to an average under 0.1 mrad across the bar and across the entire stack. Time resolved spectra are used to investigate the dynamic locking behavior with the goal of achieving a locking speed comparable to the rise time of the current (100 μs). Experimental results for multi-kW laser systems are presented, both in CW and soft pulsed operation modes.