Damage Threshold Measurements Using Femtosecond Excimer-Laser

In the UV spectral range commonly excimer lasers with a pulse length of 20 - 30 ns are used for damage testing of optical components. In this paper we present for the first time damage threshold data measured with a KrF excimer laser (248 nm) of 560 fs pulse duration. The tested materials were several UV transmitting crystals, fused silica, and dielectric coatings. The comparison of the threshold data with the respective nanosecond laser results at the same wavelength reveals that in all cases lower damage thresholds are obtained. However, the decrease in threshold was not as strong as could be expected from the more than 4 orders of magnitude higher pulse power density at the same fluence level. Transmission measurements indicate a strong decrease of the transmitted radiation with increasing pulse power below the onset level of damage, which can be interpreted by enhanced multiphoton absorption.