We present experimental and theoretical results on aberration control in solid state laser amplifiers and resonators. In lasers with diffraction-limited beam quality, aberrations cause diffraction losses that reduce the output power. In laser amplifiers, aberrations degrade the beam quality of the amplified beam. Adaptive optics can be used to correct for the aberrations and thus increase output power and beam quality. The required precision of the adaptive aberration correction can be estimated with a simple mode expansion model in which an aberrated TEM 00 mode is expanded into Hermite-Gaussian modes. Apart from these theoretical results we will present experimental results for a MOPA (MasterOscillator-Power-Amplifier) laser system consisting of a Nd:YVO 4 master oscillator and two Nd:YAG power amplifiers. A micromachined deformable mirror was used in a closed-loop system to correct for the thermo-optic aberrations of the amplifiers. A beam with a beam quality of M 2 = 2.5 at an output power of 80 W was obtained. The deformable mirror was controlled by a genetic algorithm.
We present a rugged and reliable real-time laser beam tracking system operating with a high speed, high resolution piezo-electric tip/tilt mirror. Characteristics of the piezo mirror and position sensor are investigated. An industrial programmable automation controller is used to develop a real-time digital PID controller. The controller provides a one million field programmable gate array (FPGA) to realize a high closed-loop frequency of 50 kHz. Beam tracking with a root-mean-squared accuracy better than 0.15 µrad has been laboratory confirmed. The system is intended as an add-on module for established mechanical mrad tracking systems.
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