Method and apparatus for receiving ultrasonic waves by optical m

Details Method and apparatus for receiving ultrasonic waves by optical m Method and apparatus for receiving ultrasonic waves by optical m

1981-07-01

1983-06-21

Ciarlante, Anthony V.

Measuring and testing

Vibration

Sensing apparatus

G01N 2900

Patent

active

043888321

ABSTRACT:
In an apparatus for receiving ultrasonic waves by optical means a laser beam illuminates a workpiece surface at which ultrasonic waves are manifest in the form of cyclically occurring surface deformations. The reflected light is transmitted to an optical interferometer as a measuring light beam and the beam exiting from the interferometer is converted to an electrical signal and amplified to provide a measuring beam responsive electrical signal. A portion of the laser beam immediately before being incident on the workpiece surface is also passed through the interferometer as a comparison beam. The exiting comparison beam light is converted to an electrical signal, amplified and time delayed to provide a comparison beam responsive electrical signal. By means of a subtracting circuit the comparison beam responsive electrical signal is subtracted from the measuring beam responsive electrical signal to provide a difference signal which is evaluated. The time delay is adjusted to cause the difference signal to be free of the frequency and amplitude responsive variations of the laser beam. In a Michelson type interferometer both light beams traverse the same paths in the same direction, but spatially separated. In a Mach-Zehnder interferometer both light beams traverse the same paths in respective opposite directions.

REFERENCES:
patent: 3355934 (1967-12-01), Foster
patent: 4265122 (1981-05-01), Cook et al.
patent: 4345475 (1982-08-01), Bickel

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