The generation and the detection of ultrasound at distance by lasers present many advantages over conventional piezo-electric based methods. In particular, it can be used on surfaces of complex geometry and on products at elevated temperature on a production line [1,2]. Detection has been so far usually performed by using interferometers with passive elements, the most useful being the confocal Fabry-Perot interferometer used in a transmission or reflection mode. [1,3–5].