Laser induced damage threshold of 266 AR coatings with different coating designs

The laser induced damage thresholds (LIDT), N-on-1 test at 266 nm HfO(2)/SiO(2) AR coatings, were measured for a 2 layer and 4 layer antireflection (AR) coating designs on fused silica. LIDT values for the 2 layer AR coating exhibited a constant threshold level over a wide range of increasing number of laser pulses. LIDT values for the 4 layer AR coating decreased relatively rapidly with increasing pulses in comparison. The projected lifetime of the 2 layer coating design was thus determined to be much longer than that of the 4 layer design. To explain the observed LIDT performance differences, this study effort employed the following metrological techniques: 1) Measurement of the surface roughness with a surface profile interferometer, 2) Analysis of material crystal structure with X-ray diffractometry, 3) Examination of surface damage morphology, 4) Spectrophotometric analysis of the reflectance of AR coatings, 5) Investigation of the electric filed distribution utilizing optical coating design software, and 6) Calculation of the maximum temperature rise.