<title>Phase conjugation for improving the beam quality of solid state and excimer lasers</title>

Abstract

The beam quality of high average power solid state lasers degrades due to thermal lensing and stress birefringence, similarly, discharge inhomogeneities limit the performance of excimer lasers. To improve the beam quality, self-pumped phase conjugating mirrors based on stimulated Brillouin scattering (SBS) were applied in different oscillator and master oscillator power amplifier systems (MOPA) producing radiation from the mid infrared down to the ultraviolet range. Pulsed Nd-lasers for industrial applications with up to 500 W average output power of 1 micron wavelength and high beam quality were realized. Due to phase conjugation the beam diameter and divergence do not depend on the average output power. Also for medical applications, high beam quality is essential. Therefore we investigated a MOPA- system with phase conjugating mirror at a wavelength of 2.8 micron. In the ultraviolet range, a commercial XeCl laser from Lambda Physik was equipped with an SBS-mirror resulting in a self starting oscillator with phase conjugation at a wavelength of 308 nm. As an alternative to widely used SBS- materials like liquids and gases we developed a new kind of self-pumped SBS-mirror based on multimode quartz fibers. These exhibit lower SBS thresholds and therefore continuously pumped Q-switched laser systems with SBS-mirror can be realized.