Metal-dielectric dispersive mirrors for ultraviolet lasers

Abstract

We report a broadband metal-dielectric dispersive mirror (MDDM) based on Al/SiO2/HfO2 thin films operating in the near-ultraviolet (UV) region. Demonstrating the combined benefits of both the wide reflective bandwidth of aluminum in the UV region and the flexible dispersion control capability of HfO2/SiO2 multilayer films, the MDDM has a wide bandwidth, low total thickness, and precise dispersion compensation ability. We propose an initial design based on a shortwave reflection enhancement structure (SWRES) to prevent shortwave light from obtaining a second time-dispersion compensation in the deep metal layer. The SWRES can effectively suppress group delay dispersion (GDD) oscillations in MDDMs. The designed MDDM with low GDD oscillation, low total thickness, and a wide working band was successfully fabricated and characterized. The MDDM was used to generate 15 fs UV pulses. This study demonstrates that metal-dielectric structures can enhance the performance of UV dispersive mirrors and lays the foundation for a new generation of UV femtosecond laser equipment.