The laser conditioning of dielectric thin film HR coatings has been studied as a practical method for the improvement of the damage thresholds of large area (1.1 m dia.) high power 1064 nm laser mirrors on the LLNL 120 kJ, 100 TW Nova laser system. Both HfO2/SiO2 and ZrO2/SiO2HR coatings were conditioned by rastering with a small (∼0.2 mm) diameter beam from a pulsed (18 Hz, 8 ns) Nd-YAG laser (1064 nm). The samples were rastered at various fluences below the unconditioned damage threshold and subsequently damage tested. Large area conditioning studies were also performed using a large aperture beam of the Nova laser. The laser conditioning effect was found to be permanent. Improvements in damage threshold due to conditioning were as high as a factor of 2.7 and were dependent on the conditioning parameters. A model for the conditioning effect is proposed based on the emptying of electronic defect levels within the bandgap of the dielectric materials.

Mucins are large highly glycosylated molecules that have been postulated to interfere with certain cell-cell interactions. Steric, charge and specific signalling effects have been postulated for the inhibition by cell-surface mucin molecules. In this report we evaluate the inhibitory effects of bovine submaxillary mucin (BSM), a mucin without specific lymphocyte interactions, on lymphocyte function. BSM inhibits the adhesion of lymphocytes when coimmobilized with intercellular adhesion molecule-1 (ICAM-1) and blocks the activation of T lymphocytes when coimmobilized with anti-CD3. These data demonstrate a general mucin effect on lymphocyte adhesion and activation that is primarily steric in nature and implicates mucins as general barriers to lymphocyte-tumour cell interactions. Mucin blockade of cell-cell interactions may explain why mucinous tumours are often associated with a poor prognosis.

Multilayer HfO2/SiO2 high reflectors (HR) and polarizers show a permanent increase in their 1064-nm damage thresholds following laser conditioning at subthreshold fluences. Threshold increases of 2–3x are typical. In an effort to better understand the conditioning effect we have made laser conditioning and electronic property measurements on single layers of these two materials. The laser damage threshold of 1-μm thick e-beam deposited SiO2 was increased by laser conditioning for wavelengths ranging from 355 to 1064 nm. The damage threshold of HfO2 single layers was not influenced by sub-threshold illumination. As-deposited thin films of a-SiO2 are known to contain paramagnetic electronic defects. We have used electron paramagnetic resonance (EPR) to study the concentrations and types of defects present in single layer and multilayer films of HfO2 and SiO2. E' and oxygen hole centers with concentrations on the order of 1017/cm3 have been measured in the SiO2 layers. A previously unreported defect has been observed for HfO2. The concentration of defects was studied both before and after laser conditioning and damage with 1064-nm photons. These electronic structure measurements are discussed in relation to an electronic defect model for laser conditioning of dielectric multilayers.

We are completing a thorough expansion of the laser-induced damage-test capabilities at LLNL which allow us to conduct tests under a variety of parameter conditions. We have nine different laser systems which cover the following parameter space: LaserWavelength (nm)Max. PRF (Hz)Duration (ns)Peak Fluence (J/cm2)Reptile 11064301065Reptile 2/4532, 266101040, 25Reptile 3355101040Chameleon 31064, 532, 355, 266103> 50Chameleon 101064, 532, 355, 2661010> 50Raster Blaster106417.8860Variable Pulse Laser (VPL)1064Single shot1–100> 70Kilroy106460006510Felix350, 2481002030 We describe details of the physical configurations of the individual systems, laser and sample diagnostics, and general testing procedures and capabilities. Damage test results are presented in a companion paper at this conference — “Laser Damage Database at 1064 nm”.

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