Directional detection of laser-generated ultrasound with an adaptive two-wave mixing photorefractive configuration

We report directional detection of laser-generated ultrasonic waves in real as-processed objects using holographic adaptive configuration. The scheme is based on two-wave mixing in the photorefractive crystal where holographi c recording occurs through the drift mechanism. Directional detecting prope rties are achieved by projecting the object surface irradiated by a broad p robe beam onto the photorefractive sample plane. An additional slit apertur e, whose orientation determines the direction of the maximal detection sens itivity, is put behind the sample into the reference wave. Its overall outp ut intensity is measured by a single integrating photodiode. Experimental r esults for the scheme using Bi12SiO20 and operating at lambda = 532 nm are presented to demonstrate the idea of the proposed technique. (C) 2001 Elsev ier Science B.V. All rights reserved.