Measurement of the photorefractive grating phase shift in a polymer by an ac phase-modulation technique

The complex coupling constant of a photorefractive polymer was measured as a function of an applied electric field by use of a modified ac phase modulation technique. We determined that both a photorefractive index grating and a nonphotorefractive absorption grating were present. The electric field dependencies of the amplitude and the phase of the photorefractive gain coefficient were accurately described by standard photorefractive theory. The accuracy of the photorefractive phase shift as measured by this phase-modulation technique was +/-1 degrees near phase shifts of 90 degrees and +/-3 degrees near phase shifts of 45 degrees. (C) 1998 Optical Society of America.