Ammonia hardening of porous silica antireflective coatings

Philippe F. Belleville; Herve G. Floch

doi:10.1117/12.188957

13 October 1994 Ammonia hardening of porous silica antireflective coatings

Philippe F. Belleville, Herve G. Floch

Proceedings Volume 2288, Sol-Gel Optics III; (1994) https://doi.org/10.1117/12.188957
Event: SPIE's 1994 International Symposium on Optics, Imaging, and Instrumentation, 1994, San Diego, CA, United States

Abstract

The adhesion of sol-gel antireflective porous silica coatings on vitreous optical substrates has been dramatically improved by exposure to ammonia vapors or a dip in basic solutions. The approximately 70 to 270-nm thick coatings consisted of monolayers of spherical, 20-nm diameter amorphous silica particles deposited from ethanolic colloidal suspensions by conventional liquid coating techniques. Although, the as-deposited coatings had only low adhesion and were easily damaged when cleaned by standard drag-wiping procedures, coatings exposed over 5 hours to ammonia vapors passed both adhesive-tape and moderate abrasive- resistance tests. The increase in strength was accompanied by a roughly 20% shrinkage of the original coating thickness but the antireflective properties were retained. Our explanation of this chemical effect is a base-catalyzed phenomenon leading to surface silanol condensation and hydrogen-bonding of neighbor silica particles. In addition, since this basic treatment enhanced the laser damage resistance, such strengthened antireflective coatings have been successfully evaluated on flashlamps used on Phebus, Europe's most powerful laser. This allows an increase of the laser-disk pumping efficiency.

Citation Download Citation

Philippe F. Belleville and Herve G. Floch "Ammonia hardening of porous silica antireflective coatings", Proc. SPIE 2288, Sol-Gel Optics III, (13 October 1994); https://doi.org/10.1117/12.188957

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