High-efficiency, dielectric multilayer gratings optimized for manufacturability and laser damage threshold

摘要

Ultrashort pulse, high-intensity lasers offer new opportunities for the study of light-matter interaction and for inertial confinement fusion. A 100 Terawatt laser operating 400 fs and 1.053 (mu)m is operational at LLNL, and a 1000 Terawatt (Petawatt) laser will come online in early 1996. These lasers use large-aperture (40 cm and 94 cm diameter, respectively) diffraction gratings to compress the amplified laser pulse. At present, hologrphically produced, gold overcoated photoresist gratings are used: these gratings represent the fuse in the laser chain. Higher laser damage thresholds and higher diffraction efficiencies are theoretically possible with multilayer dielectric gratings (MDG's). A number of design parameters regarding both the multilayer stack and the etched grating structure can be optimized to maximize the laser damage threshold and also improve the processing latitude for the interference lithography and reactive ion etching steps used during manufacture of these gratings. This paper presents model predictions for the behavior of hafnia/silica MDG's both during processing and in operation, and presents experimental data on the diffraction efficiency and short- pulse laser damage threshold for optimized witness gratings.