Laser Generation of Annular Converging Surface Acoustic Waves

Abstract

Converging surface acoustic waves have been generated and detected u s i n g a noncontacting technique. A YAG l a s e r together w i t h an axicon lens produces a focussed o p t i c a l r i n g which e x c i t e s both converging and d i v e r g i n g SAW on t h e t e s t sample. An o p t i c a l i n t e r f e r o m e t e r i s used t o measure t h e v e r t i c a l displacement o f t h e SAW. V a r i a t i o n s i n t h e surface acoustic waveforms due

Phase changes of ultrasonic bulk waves through focusing measured using a noncontact ultrasonic method

“…This extra phase shift must be factored in when using this method to measure the elastic properties of the sample. This has been shown qualitatively by previous workers, 5 by performing the forward problem of phase shifting the initial pulse by /2 and visually comparing it to experimental data.…”

“…This type of experiment has been reported qualitatively by earlier workers using a less sensitive detector with a lower bandwidth. [4][5] What has not been reported previously is that one is also able to measure the elastic properties of the material in one measurement, without any diffraction losses, by comparing the inward travelling wave pulse to the outward travelling wave pulse, provided that the radial displacement of the detector is known. Frequency dependent velocity and attenuation can be calculated using a fast Fourier Transform approach.…”

Axicon as a retroreflector in open-path Fourier transform infrared spectrometry

“…5 The line-focusing property of axicons has been utilized in solar energy concentrators 6,7 and laser systems. 8 The imaging properties of conic axicons have been covered in a number of publications. 5,[9][10][11][12] To our knowledge, our work represents the first time an axicon has been employed as the retroreflector in OP/FT-IR spectrometry.…”