Influence of laser conditioning on the damage properties of HfO2 thin film

The effects of different laser fluences on the optical properties of HfO2 thin films mainly including damage threshold and damage morphology, are studied under 1-on-1 condition. In experiment, the energies of 10%, 30%, 50% and 70% of the threshold energy are used to condition the HfO2 films in 1-on-1 mode. After conditioning, the surface roughness decreases from 2.62 nm to 2.41 nm. With the energy increasing, the transmittance at 1064 nm is enlarged with conditioning. The damage threshold is increased firstly, and then decreases. When the energy is 30% of the threshold energy, the damage threshold reaches the maximum value of 26.86 J/cm2 and increases by 56%. Comparing the damage morphology between conditioning and without conditioning, after the film is conditioned with 30% of the threshold energy, the damage depth under 140 mJ laser irradiation decreases from 98 nm without conditioning to 30 nm and the damage spot number decreases from 5 to 1. The experiment result shows that inclusions are the main factors of threshold decrease and conditioning with low laser fluences has the effect of decreasing the defects and solidifying the film, thus it can improve the laser-damaged threshold of films.