A sol-gel derived AgCl photochromic coating on glass for holographic application

Abstract

A sol-gel derived photochromic glass coating of about 1.5 µm in thickness is synthesized by infiltration of Ag+ into a predried Na-Al-B-Si gel layer. The formation of small Ag colloids is initiated by a soft heat treatment and the colloids are converted by a HCl vapour treatment into AgCl crystallites of about 40 nm in diameter. The coating darkens by UV irradiation, forming Ag crystallites of about 5 nm in size. This process is completely reversible at 400°C and no decay is observed in numerous cycles. An amplitude hologram which acts as a diffraction grating with a grating period of about 10 µm can be produced within this layer by a two-wave mixing experiment with laser light of 351 nm wavelength. The diffraction efficiency of this grating is determined to 0.11 %. After thermal erasing the diffraction pattern can be rewritten and erased repeatedly without any loss of efficiency.