which cannot be identified directly by an optical receiver: to do this it is first necessary to transform the phase modulation into an amplitude modulation (in this case, in a modulation of luminous intensity ). Ultrasound detection can therefore be divided into 3 steps: the conversion from ultrasound to phase-modulated optical signal, the transition from phase modulation to amplitude and finally the reading of the amplitude modulated signal with consequent conversion into an electrical signal. Industrial applications Well established applications of laser-ultrasonics are composite inspections for the aerospace industry and on-line hot tube thickness measurements for the metallurgical industry. Optical generation and detection of ultrasound offers scanning techniques to produce ultrasonic images known as B- and C-scans, and for TOFD (time-of-flight-diffraction) studies. One of the first demonstrations on small defects (as small as 3mm x 3mm) in composites was demonstrated by Dewhurst and Shan in 1993, for which they were awarded an outstanding paper award by the American Society for Non-Destructive Testing in 1994. This was also the time when significant developments on composite examinations were developed from the National Research Council of Canada and elsewhere. A wide range of applications have since been described in the literature. References Laser applications Nondestructive testing Acoustics Ultrasound