Photorefractive Laser Ultrasound Spectroscopy for Materials Characterization
Ultrasonic elastic wave motion is often used to measure or characterize material properties. Through the years, many optical techniques have been developed for applications requiring noncontacting ultrasonic measurement. Most of these methods have similar sensitivities and are based on time domain processing using interferometry1. Wide bandwidth is typically employed to obtain real-time surface motion under transient conditions. However, some applications, such as structural analysis, are well served by measurements in the frequency domain that record the randomly or continuously excited vibrational resonant spectrum. A significant signal-to-noise ratio improvement is achieved by the reduced bandwidth of the measurement at the expense of measurement speed compared to the time domain methods. Complications often arise due to diffuse surfaces producing speckle that introduces an arbitrary phase component onto the optical wavefront to be recorded. Methods that correct for this effect are actively being investigated today.
KeywordsReference Beam Photorefractive Crystal Electronic Speckle Pattern Interferometry Photorefractive Effect Space Charge Field
Unable to display preview. Download preview PDF.
- 1.J. W. Wagner, “Optical Detection of Ultrasound,” Physical Acoustics, Vol. XIX, Eds. Thurston, R.N., and Pierce, A.D., (Academic Press, New York, 1990) Chp. 5.Google Scholar
- 2.P. Yeh, Introduction to Photorefractive Nonlinear Optics, (John Wiley, New York, 1993).Google Scholar
- 3.S. I. Stepanov, International Trends in Optics, (Academic Press, New York, 1991) Chp. 9Google Scholar
- 11.T.C. Hale, K.L. Telschow and V.A. Deason, “Photorefractive optical lock-in vibration spectral measurement,” submitted for publication to Applied Optics.Google Scholar