Investigation of photoacoustic signal strength as a function of scan-speed and laser-repetition-rate

Optical-resolution photoacoustic microscopy (OR-PAM) can produce micron-scale, high-resolution images of optically-absorbing chromophores. The pressure rise of photoacoustic signals is proportional to the Grueneisen parameter, which is temperature dependent. High laser repetition-rates may cause overlapping of adjacent laser pulses on targets in laser-scanning OR-PAM. When laser-pulse-repetition intervals are shorter than thermal relaxation times, the zone of laser-spot overlap between pulses can generate higher photoacoustic signal than cases where beam-spots do not overlap or in cases where laser pulse-intervals are longer than the thermal relaxation time. This is because subsequent laser pulses experience higher Grueneisen parameters than previous pulses due to temperature rises induced by the previous pulses. Here, we present our recent studies on photoacoustic signals strength varying with scanning speed and laser-repetition-rate on black tape, human hair and rat blood respectively.