Inscription and analysis of non-uniform diffraction gratings in azobenzene molecular glass thin films

Non-uniform surface relief diffraction gratings were laser-inscribed on azobenzene molecular glass thin films using a modified Lloyd's mirror interferometer. The azobenzene films were exposed to an adjustable interference pattern produced by the recombination of collimated and spherically divergent laser wave fronts. The localized pitch, grating vector orientation and depth of the resulting non-uniform gratings were measured using an atomic force microscope and a theoretical model was analytically developed to explain the experimental results. The fabricated gratings exhibited a chirping or pitch variation along the imposed X-axis as well as an angular change in the grating vector orientation along the imposed Y-axis. Studies were conducted on various non-uniform grating configurations having central pitches of 500 nm, 1000 nm, 1500 nm and 2000 nm.