1 November 1990 Al203.H2O-SiO2 sol-gel HR coatings for high-power laser applications
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Abstract
Pursuing our official collaborative ICF-laser search and development program at Limeil National Laboratory (LNL) with the Lawrence Livermore National Laboratory (LLNL) for high damage threshold optical coatings, we have now formally established that Sol-Gel highly reflective coatings prepared from colloids are superior to those prepared from solutions of precursor materials. Thus, single layer coatings of bohemite A1203.H20 have been prepared on fused silica and BK-7 substrates from aqueous colloidal suspensions of hydrated alumina at room temperature. Such coatings were porous and therefore revealed a measured refractive index of about 1.44, lower than the relevant dense material. These single coats when laser damage tested, have exhibited thresholds, under S-on-i irradiation mode (S shots at the same fluence onto a selected site) of respectively i2-i4 J/cm2 with 3-ns pulses and 35-50 i/cm2 with-i6 ns pulses at 30-Hz. Multilayer, high reflectivity, dielectric coatings were also prepared at room temperature by laying down quarterwave-thick, alternating coats of this alumina with silica also prepared from colloidal sol, and having a refractive index of 1.22. To achieve 99% reflectivity 32 to 36 total layers were required. Such HR-coatings revealed damage thresholds as good as those of single layers of the constituting oxides in the same laser conditions.
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Herve G. Floch, Herve G. Floch, J. J. Priotton, J. J. Priotton, Ian M. Thomas, Ian M. Thomas, } "Al203.H2O-SiO2 sol-gel HR coatings for high-power laser applications", Proc. SPIE 1328, Sol-Gel Optics, (1 November 1990); doi: 10.1117/12.22569; https://doi.org/10.1117/12.22569
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