HETERODYNE TECHNIQUE FOR THE DIRECT MEASUREMENT OF THE AMPLITUDE AND PHASE OF PHOTOREFRACTIVE SPACE-CHARGE FIELDS

A heterodyne technique is presented for the independent, direct measur ement of the amplitude and phase of photorefractive space-charge field s during uninterrupted buildup and photoinduced decay. The technique i s based on using a probe beam with a frequency slightly different from that of the two recording beams to continuously read photorefractive phase gratings during all stages of formation and decay. The probe bea m is virtually collinear with one of the recording beams. The beat bet ween the diffracted component of the frequency-shifted probe beam and the transmitted component of the recording beam produces a heterodyne beam component. This heterodyne component contains the photorefractive grating information and is monitored to yield the amplitude and phase of the photorefractive fields. This nondestructive characterization t echnique exhibits excellent sensitivity and permits photorefractive ph ase measurements to within 1.5-degrees.