Investigation of fs-laser induced damage on high reflection mirrors used for 800Â nm broadband pulse compression gratings

High reflection mirror for 800 nm broadband pulse compression grating was fabricated by electron beam evaporation using three dielectrics (Ta2O5/SiO2/HfO2). It has more than 99% reflectance with bandwidth larger than 160 nm around wavelength of 800 nm and 84.3% transmission at the exposure wavelength of 413 nm. Laser-induced damage behaviors of the mirror were investigated by 800 nm TE polarization laser with pulse width τp of 40-100 fs. The laser damage threshold of the mirror observes a fitting scaling law of τp0.29. The damage characters and near field distribution consistently indicated that the initial damage of the mirror was ascribed to nonlinear ionization in the zone position of electric field intensity maximum. The experimental threshold can be fitted with a model based on electron production taking into account photoionization and avalanche ionization. The mirrors with good spectral properties and high laser damage threshold provide a solid base for fabricating 800 nm pulse compression gratings.