Comparison between 355 nm and 1064 nm damage of high grade dielectric mirror coatings

Advanced reactive e-beam evaporation process was used to deposit HfO2/SiO2HR coatings for 355 nm high power laser applications. Atomic force microscopy studies and Nomarski microscopy have shown that the defect density of these coatings is extremely low exhibiting nearly no nodular defects known for an increased susceptibility to laser damage in the IR spectral region. Standard damage testing (conditioned and unconditioned) was conducted at LLNL- at 355 nm (3 ns) for normal (0 deg) and nonnormal-incident designs (45 deg). Damage threshold between 5 J/cm2 and 8 J/cm2 were obtained. No significant conditioning effect could be demonstrated. The same evaporatin technique was used to manufacture normal incident HfO2/SiO2HR coatings for 1064 nm wavelength from 2 different types of evaporant grade HfO2 as well as from a Hf metal source. Damage test results, as well as defect concentrations and conditioning effect, were compared to the 355 nm samples. Moreover, care was taken on the detection of the origin of damage at fluences near the damage thresholds.