Combined advanced finishing and UV-laser conditioning for producing UV-damage-resistant fused silica optics

Abstract

Laser induced damage initiation on fused silica optics can limit the lifetime of the components when used in high power UV laser environments. Foe example in inertial confinement fusion research applications, the optics can be exposed to temporal laser pulses of about 3-nsec with average fluences of 8 J/cm 2 and peak fluences between 12 and 15 J/cm 2. During the past year, we have focused on optimizing the damage performance at a wavelength of 355-nm (3ω), 3-nsec pulse length , for optics in this category by examining a variety of finishing technologies with a challenge to improve the laser damage initiation density by at least two orders of magnitude. In this paper, we describe recent advances in improving the 3ω damage initiation performance of laboratory-scale zirconium oxide and cerium oxide conventionally finished fused silica optics via application of processes incorporating magnetorheological finishing (MRF), wet chemical etching, and UV laser conditioning. Details of the advanced finishing procedures are described and comparisons are made between the procedures based upon large area 3ω damage performance, polishing layer contamination, and optical subsurface damage.

MRF applications: on the road to making large-aperture ultraviolet laser resistant continuous phase plates for high-power lasers

“…Additional material removal beyond the minimum implemented in each step enabled us to build in safety factors to ensure obtaining a finished optic with minimal or no subsurface damage. As with our previous work 12 , MRF final figuring and HF acid etching form part of this fabrication process. The damage test results of several large-aperture optics, main debris shields (MDS), CPP substrates, and diffractive grating substrates, tested during this development effort are shown in Figure 4.…”

“…In 2002, we introduced an advanced finishing process that exhibited superior damage performance of fused silica at 351 nm 12 . The process uses MRF final finishing on fused silica to attain final figure and superior damage performance once combined with HF acid etching to remove MRF related contaminants such as iron and ceria.…”

“…Our MRF imprinting development has mainly focused on manufacture of CPPs for use in the infrared portion (1053 nm) of high-power laser systems 11 . Combining this technology with advanced MRF finishing techniques that focus on ultraviolet laser damage resistance 12 makes it potentially feasible to manufacture large-aperture CPPs that can operate in the ultraviolet (351 nm) without sustaining laser-induced damage.…”

Developing magnetorheological finishing (MRF) technology for the manufacture of large-aperture optics in megajoule class laser systems

“…8,14 The process uses MRF final finishing on high-purity "inclusion-free" fused silica substrates to attain final figure and superior damage performance once combined with HF acid etching to remove MRF Recipe for MRF process to improve laser damage resistance. The general approach is to eliminate subsurface damage and near surface contamination using MRF and post-processing such that the surface and near surface "look" like bulk material.…”

Effect of thermal anneal on growth behavior of laser-induced damage sites on the exit surface of fused silica

“…While advances have been made in bulk purification and surface finishing methods for optical materials [ (Menapace, Penetrante et al 2002), (Suratwala, Miller et al 2011)], localized damage on optical components used in high power laser systems continues to limit their operational lifetime. The initial size of such damage sites is highly dependent on laser conditions [ (Carr, Trenholme et al 2007), (Carr, Cross et al 2011)] but range from a few microns to a few tens of microns for nanosecond pulses.…”