New phase modulator with large stroke and high bandwidth for improved coherent coupling schemes

Kurzfassung

Throughout the past years the scaling of laser brightness by building larger laser oscillators stagnated. Therefore, alternative methods termed coherent beam combining moved to the centre of interest in research to increase the laser brightness using multiple separate laser systems. Especially, in the case of master oscillator (MO) power amplifier (PA) systems the control of phase noise introduced by the power amplifier posts a promising approach \[1, 2\]. Our thin disc PA system tends to introduce large phase strokes over a large range of frequencies, which typically would be approached by the use of a ‘‘woofer / tweeter'' arrangement. Woofer and tweeter setups add to the complexity of the servo loop. Therefore, we decided to amplify the phase stroke of a piezo phase modulator optically to work towards a high phase stroke of several lambda as well as several 10 kHz of servo loop bandwidth.