We have completed a fifteen-year, referenced and documented compilation of more than 15,000 measurements of laser-induced damage thresholds (LIDT) conducted at the Lawrence Livermore National Laboratory. These measurements cover the spectrum from 248 to 1064 nm with pulse durations ranging from < 1 ns to 65 nm and at pulse-repetition frequencies from single shots to 6.3 kHz. We emphasize the changes in LIDTs during the past two years since we last summarized our database. We relate these results to earlier data concentrating on improvements in processing methods, materials, and conditioning techniques. In particular, we highlight the current status of anti-reflective coatings, high reflectors, polarizers, and frequency-conversion crystals used primarily at 355 nm and 1064 nm.

A historical perspective on fifteen years of laser damage thresholds at LLNL

Two types of coatings were evaluated with respect to their suitability for optical applications in which low scattering is required. The plasma-deposition technique produces dense pinhole-free films of refractory materials from a glow discharge plasma at typical substrate temperatures of 200–300°C. Plasma-deposited films of SiO2 and Si3N4, produced from reactions of SiH4 with N2O and NH3, respectively, were evaluated in this study. SiO2 films were also produced from metal-organic precursor solutions using dipping and spinning application techniques followed by pyrolysis at 600°C. Coatings were deposited on the highest quality substrates available, which were characterized prior to deposition so that the effects of the coatings could be separated from those of the substrates. Nomarski microscopy, surface profiling, total integrated scattering, ellipsometry, and photon backscattering techniques were used for characterization. The properties of these coatings and information on how the quality depends on coating conditions are reported in this paper.

Characterization of plasma-deposited and dip-coated films for critical optical applications.

Laser damage threshold measurements in the ultraviolet' (UV) have been made at the Lawrence Livermore National Laboratory (LLNL) since 1979. These tests were conducted using single pulses at the third (355 nm) and fourth (266 nm) harmonic wavelengths of 1064-nm Nd-glass lasers, and single and repetitively fired pulses from KrF (248 nm) and XeF (351 nm) excimer lasers respectively. Surface damage thresholds of dielectric thin films, antireflective (AR) coatings, highly reflective (HP) coatings, and porous and graded-index AR coatings, as well as surface and bulk thresholds of optical windows and crystals have been measured. More than twenty different parameter studies have been conducted to develop materials with increased laser damage thresholds.

Review of uv laser damage measurements at Lawrence Livermore National Laboratory

A summary is given of the principal aspects of laser-induced damage to polished optical surfaces and dielectric, thin-film, high-reflectivity and antireflective coatings. Methods for producing porous antireflective surfaces and coatings and their damage properties are also reviewed. Finally, new areas of basic research to solve current and future problems are addressed.

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Effects of laser radiation on surfaces and coatings

Highly damage-resistant, broadband, hard AR coating for high-power lasers in the UV to near-IR wavelength regions

We used 355-nm, 0.6-ns pulses to measure laser-damage thresholds of porous-silica antireflection coatings deposited from a polymer solution onto fused silica substrates. For 118 coatings with optical thickness of 500 to 600 nm, the median threshold was less than 2 J/cm/sup 2/, and thresholds were not systematically dependent on either the level of filtration of the coating solution or the procedure used to clean the substrates. For coatings 87 to 90 nm in optical thickness, thresholds were as large as 9 J/cm/sup 2/, which is the threshold of the bare polished surfaces of the fused silica substrates. The data suggests that carbon residues from the coating solution are responsible for damage in the thicker coatings.

Laser Damage in Porous-Silica Antireflection Films

An XeF laser-damage experiment was used to measure damage thresholds for bare polished crystals of CaF/sub 2/ and porous silica antireflection coatings on fused silica substrates Damage was induced by applying 1000 350-nm, 25-ns pulses at repetition rates of 25 to 100 Hz to small (typically 012 x 03 cm) sites on the surfaces of the sample Eight samples of fluorescence-free CaF/sub 2/ exhibited both surface and bulk damage at fluences as low as 10 J/cm/sup 2/ Three samples of UV-grade CaF/sub 2/ also had surface damage thresholds of 10 J/cm/sup 2/, and bulk damage was not observed in this material Thresholds for the porous silica coatings were 17 to 23 J/cm/sup 2/

JG Wilder

Papers

Laser Damage in Porous-Silica Antireflection Films

Thresholds Measured With 350-nm Pulses at 25–100 Hz for Bare Polished Crystals of CaF 2 and for Silica Sol-gel AR Coatings on Silica Substrates

Damage-resistant porous silica antire-flection coatings for use at 351, 266, and 248 nm