Development Of A Backward-Mode Photoacoustic Microscope Using A Fabry-Perot Sensor

Optical-resolution photoacoustic microscopy (PAM) has been shown to enable the acquisition of high resolution (mu m) functional and anatomical images. For backward-mode operation, conventional piezoelectric ultrasound transducers need to be placed far away from the signal source due to their opacity and size. This can result in reduced acoustic sensitivity. Planar Fabry-Perot polymer film interferometer (FPI) sensors have the potential to overcome this limitation since they are transparent to the excitation wavelength, can be placed immediately adjacent to the signal source for high acoustic sensitivity, and offer a broadband frequency response (0 -50 MHz).In this study, we present a high frame rate, backward-mode OR-PAM system based on a planar FPI ultrasound sensor. A ns-pulsed laser provides excitation pulses (< 200 nJ, maximum pulse repetition frequency = 200 kHz, 532 nm) to generate photoacoustic waves that are detected using a planar FPI sensor interrogated at 765-781 nm. For backward-mode operation and highest acoustic sensitivity, the excitation and interrogation beams are coaxially aligned and raster-scanned. The optical transfer function of the sensor, the spatial resolution and the detection sensitivity were determined to characterise the set-up. Images of a leaf phantom and first in vivo images of zebrafish larvae were acquired.This approach will enable fast 3D OR-PAM with high resolution and high sensitivity for functional and molecular imaging applications. FPI-based ultrasound detection also has the potential to enable dual-mode optical- and acoustic-resolution PAM and the integration of photoacoustic imaging with purely optical modalities such as multi-photon microscopy.