SEDL / STP / STP1117-EB / STP26516S

1-on-1 And n-on-1 Laser Strength of Binder Aided ZrO² and ZrO²-SiO² Reflective Sol-Gel Coatings

Floch, HG
Commissariat à l'Energie Atomique Centre d'Etudes de Limeil-Valenton, Villeneuve Saint Geroges,

Priotton, JJ
Commissariat à l'Energie Atomique Centre d'Etudes de Limeil-Valenton, Villeneuve Saint Geroges,

Pages: 19    Published: Jan 1990

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Abstract

In continuation to our search program on laser-damage resistant coatings and in synergy with the Lawrence Livermore National Laboratory, we have prepared porous single layer coatings of ZrO² on fused silica and BK-7 substrates from suitable aqueous colloidal suspensions of crystalline zirconia at room temperature. By adding judiciously a soluble inorganic binder to the suspension prior to application, it has been possible to increase substantially both the coating refractive index and the abrasion-resistance. The optimum binder concentration was about 30 % and at this level the optical properties and laser damage threshold of the zirconia coating were satisfactory. Multilayer high reflectivity dielectric coatings were also elaborated by laying down quaterwave-thick, alternating coats of this binder-aided zirconia with silica, also prepared from colloidal suspension. To achieve 99 % reflectivity, 17–19 layers were required. Single shot (1-on-1), laser damage tests at 1064-nm wavelength with a pulse length of 3-ns were carried out on both the single layer and multilayer systems. The thresholds averaged 8.6 and 8.2 J/cm² respectively. With a laserannealing post-treatment, n-on-1 threshold values were higher than the 1-on-1 figures by a factor of about 1.5.