A miniature all-optical photoacoustic imaging probe

A miniature (250 mu m outer diameter) photoacoustic probe for endoscopic applications has been developed. It comprises a single delivery optical fibre with a transparent Fabry Perot (FP) ultrasound sensor at its distal end. The fabrication of the sensor was achieved by depositing a thin film multilayer structure comprising a polymer spacer sandwiched between a pair of dichroic dielectric mirrors on to the tip of a single mode fiber. The probe was evaluated in terms of its acoustic bandwidth and sensitivity. Ultra high acoustic sensitivity has been achieved with a concave FP interferometer cavity design, which effectively suppresses the phase dispersion of multiple reflected beam within the cavity to achieve high finesse. The noise equivalent noise (NEP) achieved is 8 Pa over a 20 MHz bandwidth. Backward mode operation of the probe is demonstrated by detecting photoacoustic signals in a variety of phantoms designed to simulate endoscopic applications. A side-viewing probe is also demonstrated illustrating an all-optical design for intravascular imaging applications.