Spatial-offset pump-probe imaging of nonradiative dynamics at optical resolution

Nonradiative photothermal (PT) and photoacoustic (PA) processes have found widespread applications in imaging, stimulation, and therapy. Mapping the generation and propagation of PA and PT waves with high resolution is important to elucidate the interaction between nonradiative fields and biological systems. To this end, we introduce spatial-offset pump-probe imaging (SOPPI). By spatially offsetting the pump beam and the probe beam, SOPPI allows simultaneous imaging of PA/PT wave propagation with nanosecond temporal resolution, micrometer spatial resolution, 65-megahertz detection bandwidth, and a sensitivity of 9.9-pascal noise equivalent pressure. First, the PA and PT evolution from a fiber emitter and the subsequent wave interaction with a mouse skull and brain slices are demonstrated. Then, using water as the absorber, a wavelength-dependent PA/PT generation, evanescent wave-generated PA, and a back-propagated acoustic Mach cone with a tapered fiber are recorded. At last, a SOPPI-PACT is developed to reconstruct the pigment distribution inside a zebrafish larva with high precision and signal-to-noise ratio.