ABSTRACT
The paper presents an overview of the benefits of recording phase masks into the bulk of photo-thermo-refractive glass. We demonstrate that both binary and gray-scale phase masks can be encoded into the medium, and that such masks can be used for mode conversion and beam shaping with near-theoretical efficiency. We further demonstrate that by encoding the phase mask profile into a transmitting volume Bragg grating, it is possible to create tunable and achromatic phase masks without requiring a complex phase pattern.
ABSTRACT
A novel photothermal process to spatially modulate the concentration of sub-wavelength, high-index nanocrystals in a multicomponent Ge-As-Pb-Se chalcogenide glass thin film resulting in an optically functional infrared grating is demonstrated. The process results in the formation of an optical nanocomposite possessing ultralow dispersion over unprecedented bandwidth. The spatially tailored index and dispersion modification enables creation of arbitrary refractive index gradients. Sub-bandgap laser exposure generates a Pb-rich amorphous phase transforming on heat treatment to high-index crystal phases. Spatially varying nanocrystal density is controlled by laser dose and is correlated to index change, yielding local index modification to ≈+0.1 in the mid-infrared.
