AN OPTICAL-FIBER INTERFEROMETER FOR REMOTE DETECTION OF LASER-GENERATED ULTRASONICS

A 15 MHz bandwidth active homodyne fibre-optical interferometer for re mote detection of laser-induced ultrasonic waves in metallic and non-m etallic targets is reported. The fibre interferometer design and assoc iated electronics are described in sufficient detail for it to be easi ly constructed. The interferometer uses a low-power He-Ne laser and th e reflected signal from the natural surface of the target at a distanc e of 200 mm. Despite its use of an open air path in the sensing arm an d an ail-fibre design, the interferometer achieved a single-pulse nois e equivalent displacement of 0.4 nm and a figure of merit of 0.1 pm Hz (-1/2).