Phase conjugation for improving the beam quality of solid state and excimer lasers

ABSTRACT The beam quality of high average power solid state lasers degrades due to thermal lensing and stress birefringence, similarly,discharge inhomogenities limit the performance of excimer lasers. To improve the beam quality, self-pumped phaseconjugating mirrors based on stimulated Brillouin scattering (SBS) were applied in different oscillator and master oscillatorpower 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 at 1 micron wavelength and highbeam quality were realized. Due to phase conjugation the beam diameter and divergence do not depend on the averageoutput power. Also for medical applications, high beam quality is essential. Therefore we investigated a MOPA-system withphase conjugating mirror at a wavelength of 2.8 micron. In the ultraviolet range, a commercial XeCl laser from LambdaPhysik was equipped with an SBS-mirror resulting in a self starting oscillator with phase conjugation at a wavelength of308 nm.As an alternative to widely used SBS-materials like liquids and gases we developed a new kind of self-pumped SBS-