Photodeposition of Diffraction Gratings in Glass: A Comparison of Lithographic, Laser Writing and Holographic Deposition

Abstract

High-resolution holographic gratings with line spacings ranging from 8 to 50 μm have been achieved by 488 nm photolysis of porous glasses impregnated with Fe(CO)5. The interference pattern created with a Mach–Zehnder interferometer and Ar+ laser creates a pattern of well-resolved, parallel regions possessing a refractive index and optical density different from those of the bulk glass. Line spacings were calculated from the diffraction of a He–Ne laser and corroborated by optical microscopy. Comparing the optical performance of gratings prepared holographically with those produced by direct laser writing or photolithography establishes significant improvements in the uniformity of the deposited gratings and optical performance. Thermal consolidation of the porous glass at 1200 °C decreases sample volume and line spacing in direct proportion to the decrease in the dimension perpendicular to the grating lines. Consolidation not only improves optical performance by reducing line spacing, but encapsulates the grating within the glass matrix, thereby creating a grating that is unaffected by high laser powers, insensitive to UV excitation, and stable under a variety of environmental and chemical conditions.