The characteristics of an interferometric system based on two-wave mixing at 1.06 mm in photorefractive InP:Fe under an applied field for the detection of ultrasonic motion of a scattering surface are described. A theoretical analysis of possible configurations for the detection of small phase modulation in the undepletedpump approximation is presented. Experimental assessment of the device for both cw and pulse regimes is performed: The sensitivity, the e'tendue, the response time, and the behavior under ambient vibrations or moving inspected samples are provided. This adaptive device presents many features appropriate for industrial inspection and compares advantageously with the passive confocal Fabry-Perot device that is now widely used.