Application of Surface Relief Gratings Created on Azobenzene Functionalized Polymer Films as Phase Masks

Abstract

Holographic recording of surface relief gratings has recently been reported in side chain azo containing polymers by Kumar, Tripathy and coworkers [1-10] and Rochon, Natansohn and coworkers [11-13] It has been demonstrated that large surface modulation (>3000Å) could be inscribed in thin films of these polymers when an Argon ion laser radiation at 488 nm with a modest intensity (a few tens of mW/cm2) is used to record the gratings. This grating formation process strongly depends on the polarization states of the recording beams [4]. The gratings appear to be almost sinusoidal and recording of crossed gratings has been demonstrated[1]. These gratings are very stable when they are kept below the glass transition temperature (Tg) of the polymer. The gratings can be erased by either heating the grating sample above Tg or exposing it to a single laser beam at appropriate wavelength and with appropriate polarization [10]. This process allows a one step fabrication of complicated surface profile without the need of any pre or post processing of the polymer samples. Complex surface profiles, for example, well defined beat structures and blazed gratings have been recorded on these polymer films [8]. Since this surface relief grating formation process provides the one step processing and large surface modulation on the polymer films, such process is expected to have significant potential applications for various optical devices including diffractive optical elements.