Abstract

We report the recording of high-resolution and high-efficiency volume phase holograms in photo-thermo-refractive glasses (PTRGs). The glass material is a silicate (SiO₂-Al₂O₃-ZnO-Na₂O) doped with photosensitive components (Ce³⁺, Ag⁺) and a sensitizer (F⁻, Br⁻) fabricated at Vavilov State Optical Institute in Russia.¹ The process of inducing refractive- index changes in the silicate PTRG involves two distinct steps. First the bulk glass is exposed to ultraviolet radiation (300-350 nm), producing a distribution of metallic colloidal particles that serve as nucleating sites. Second, a thermal treatment causes the nuclei to grow into crystalline particles of a specific size, shape, and refractive index. The refractive-index difference between the bulk glass and the crystalline particles creates an index modulation in the material. In the experimental arrangement, a bipolar prism and a cylindrical lens are used to produce a sinusoidal UV interference pattern of 700 line / mm at the PTRG sample by using a frequency tripled pulsed Nd-YAG laser (353 nm). The diffraction efficiency and angular dependence of the fundamental diffracted order are measured using by He-Ne laser (633 nm). Figure f shows the diffraction efficiency as a function of the crystal thickness. This was obtained by recording 700-line/mm holograms in a 4.3mm-thick sample (at two different UV exposure of 18 and 54 J/cm² and thermal treatment at 480°C for 840 min) and reducing thy sample thickness, in steps, by surface polishing. A relative diffraction efficiency of up to 55% is observed. Figure 2 shows the angular dependence of the diffraction efficacy of a hologram recorded in the 4.3-mm-thick sample.

© 1995 Optical Society of America