2-BEAM COUPLING MEASUREMENTS OF GRATING PHASE IN A PHOTOREFRACTIVE POLYMER

We investigate in detail the grating properties of a recently discovered organic photorefractive polymer as a function of electric field by using two-beam coupling. Using an oblique-incidence geometry, we present measurements of index and absorption grating phase relative to the intensity interference pattern as well as measurements of the amplitude of both the absorption and index gratings. We find that in low electric fields a weak in-phase grating (possibly photochromic) and the low electro-optic coefficient prevent observation of a phase-shifted photorefractive grating. However, in moderate-to-high electric fields a much stronger photorefractive index grating with a phase shift approaching 90-degrees dominates. The presence of an index grating with a 90-degrees phase shift at high fields provides strong evidence that these polymers are indeed photorefractive.