A BROAD-BAND ANTIREFLECTION COATING FOR ENHANCED HOLOGRAPHIC RECORDING AND READOUT IN BISMUTH SILICON-OXIDE

We demonstrate a high-quality double-layer antireflection coating for high index (n = 2.61 at 514 nm) photorefractive and electro-optic bism uth silicon oxide (Bi12SiO20) crystals. The antireflection coating com prises two electron-beam-deposited quarter-wave dielectric lavers of M gF2 and ZrO2, and increases the beam throughput by as much as 20% per interface at normal incidence. For holographic recording applications, the antireflection coating eliminates multiple internal reflections t hat produce extraneous gratings. The combination of these two factors significantly increases the diffraction efficiency and the two-beam co upling gain. Key characteristics of the double-layer coating include a broadband minimum that encompasses typical write and read wavelengths for Bi12SiO20 With normal-incidence reflectivities of less than 0.2% at 514 nm and 1% at 633 nm, respectively, and a forgiving angular disp ersion for both TE and TM polarized waves with reflectivities of less than 2% for angles of incidence up to 45 degrees. (C) 1997 American In stitute of Physics.