Laser damage testing according to ISO 11254 was performed with an automatic testing facility. With a Qswitch Nd:YAG laser up to 700 single "1 on I " tests were performed for each measurement. A detailed description of the experimental setup is given. Damage was on-line detected by light scatter measurements. Associated problems to this method are discussed here. To evaluate the energy-depended damage frequency values from the measured data, a reliable procedure is needed; different methods are tested. For the linear extrapolation of the damage frequency values to 0% damage frequency, as prescribed by ISO, a certain selection of data points is necessary. We discuss different types of damage statistics and the problems occurring using linear extrapolation.

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SiON thin films were prepared by Ion Beam Sputter Deposition (IBS) and Ion Assisted Deposition (lAD) on polished fused-silica-and BK7-substrates. The influence of process parameters on fundamental film properties was analyzed. Investigated parameters in the AD process were gas composition, substrate temperature, ion current density, ion energy and neutralisation current. The deposition rate and the gas composition were found to be essential parameters ofthe lBS process. Film characterisation was performed by spectrophotometric analysis, laser calorimetry, laser damage testing according to ISO 11254 and X-ray spectroscopy to obtain refractive index, absorption coefficient, damagethreshold/morphology and film stoichiometry respectively. Important technical details about both deposition processes are reported.Both 5i02 and S13N4 films could be prepared with Ion Assisted Deposition and Ion Beam Sputtering. Laser damage thresholds of lAD SiOXNY films are 2. . .1 0 J/cm2. A graded index antireflection coating with 1 0 ppm absorption was prepared. The absorption of lBS Si3N4 films is higher than that of lAD films.