Interference-based amplification for CW laser-induced photoacoustic signals.

Thanks to their low cost, compactness and suitability of use in industrial environments, CW lasers represent a viable alternative to more traditional pulsed lasers for non-contact inspection of structures, both under static and working conditions. However, the lower energy density typically reached by CW lasers requires adequate attention to obtain ultrasonic signals with sufficient amplitude. CW lasers can be modulated by TTL sequences with different duty cycles to constructively use the excitation of a double ultrasonic wave, occurring when the laser is both turned on and off.