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 measurement of the amplitude and phase of photorefractive space-charge fields during uninterrupted buildup and photoinduced decay. The technique is 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 beam is virtually collinear with one of the recording beams. The beat between 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 technique exhibits excellent sensitivity and permits photorefractive phase measurements to within 1.5-degrees.