Cleaning method for improving laser induced damage threshold of multilayer dielectric pulse compressor gratings

Oxygen plasma and HPM solution (mixtures of hydrochloric acid, hydrogen peroxide, and deionized water) were applied to cleaning the multilayer dielectric (MLD) pulse compressor gratings. X-ray photoelectron spectroscopy was carried out to evaluate surface cleanliness of the gratings. It is found that photoresist and fluorocarbon residues can be efficiently removed with oxygen-plasma cleaning and metal contaminants can be completely removed with HPM cleaning. After cleaning processes, the typical diffraction efficiencies in -1st reflected order are maintained larger than 95.0% at an incidence of 66.4° in TE polarization, and the laser induced damage threshold (LIDT) for 10-ps laser pulse at 1053 nm is greatly improved to 1.6 J/cm2. The cleaning method using oxygen plasma and HPM solution can efficiently make the surface clean and therefore enhance the LIDT of MLD gratings. (authors)