TITLE:
Photorefractive Ultrasonic Sensor for Weld Quality Monitoring
AUTHORS:
S. Zamiri, M. Salfinger, M. Gruber, M. Stückler, B. Reitinger
KEYWORDS:
Photorefractive Crystal, Laser Ultrasonic, Weld Joints, Defect
JOURNAL NAME:
Open Access Library Journal,
Vol.4 No.5,
May
26,
2017
ABSTRACT: We report on a laser
ultrasonic receiver based on two wave mixings in two nonlinear
Bi12SiO20 (BSO) photorefractive crystals
and its application for welded joints inspection. The nonlinear photo
refractive crystals are operated with inverted voltages in respect to each
other. Reversal of the voltage inverts the polarity of detected ultrasonic
pulses which are generated by a pulsed laser on a sample surface. Present noise
is, however, not inverted. Subtracting both signals after the two
photorefractive crystals using a balanced photo-detector leads to suppression
of noise and to an increase in the signal/noise ratio. We demonstrate the
working principle by using a phase modulator and present laser ultrasonic
measurement and compare the results from the proposed technique with a
conventional two wave mixing interferometer based on single BSO crystal showing
that the signal to noise/rate is significantly enhanced. Finally, we show the
experimental results of application of these detectors for defects detection in
two industrial samples with welded area.