Fig. 1: All-optical forward-viewing photoacoustic endoscopy probe.

a A schematic representation of the probe. b A magnified visualization of the distal end shows individual fiber-optic cores in the coherent fiber bundle and the Fabry-Pérot (FP) ultrasound sensor. c The FP sensor is deposited on the distal end of the fiber bundle and is comprised of two dielectric mirror coatings that are sandwiched between a Parylene C spacer layer (15 µm thick)—see also Supplementary Fig. S1. d A bright-field microscope image of the tip of the fiber bundle (prior to deposition of the FP sensor), which shows a subset of the 50,000 fiber cores. Suppl. Fig. S2 shows an image of the entire bundle, which illustrates all 50,000 cores and was obtained by scanning the interrogation beam over the proximal end of the bundle with the FP sensor in situ. e The interferometer transfer function (ITF) from a single core position. Blue: the measured ITF. Red: an asymmetric Lorentzian fit to the measured ITF