Damage threshold and surface distortion measurement for high-reflectance, low-loss mirrors to 100+ MW/cm(2) cw laser intensity.

By frequency-stabilizing the output from an Erbium fiber amplifier at 1580 nm to a high-finesse cavity (finesse ~6300) formed by two high-reflectance, low-loss, concave mirrors, we achieve 22.4+/-2.0 kW intracavity circulating power and 101+/-9 MW/cm(2) cw intracavity intensities on the surfaces of the mirrors. Repeated experiments show no damage to the mirrors' coating. In addition, small variations of the mirrors' radius of curvature are observed and measured by recording the cavity's transverse-mode range. The mirrors' 10 cm radius of curvature changes as function of laser intensity at a rate of 105 mum/(MW/cm(2)).