<title>Homodyne detection of ultrasonic surface displacements using two-wave mixing in photorefractive polymers</title>

Abstract

In recent years, a number of adaptive interferometers have been used for the remote detection of laser-generated ultrasonic waves in parts under inspection. One type of adaptive interferometer uses two-wave mixing in a photorefractive material to form a real-time hologram, or adaptive beamsplitter. In this work we describe such an interferometric receiver based on two-wave mixing in photorefractive (PR) polymers. The PR polymers have a number of very promising technical features for this application which will be described in detail. In addition, the polymer composition can be tailored to specific requirements and the materials can be processed into a variety of different shapes and forms. Finally, when compared with inorganic photorefractive crystals, the polymers are inexpensive and simple to fabricate. We have taken advantage of the above features to demonstrate homodyne detection in the PR polymers with a sensitivity that is within a factor of three of the limit for an ideal homodyne system. We have also used a laboratory receiver to detect ultrasonic waves with good signal-to-noise. In this talk we will discuss the physical features of our polymer-based receiver and describe our experiments to characterize this system.