We recently introduced photoacoustic remote sensing (PARS) microscopy as an all-optical non-contact optical-resolution modality with absorption-based photoacoustic contrast. A pulsed excitation beam is optically focused into a sample then the resulting photoacoustic signal is sensed using a confocal long-coherence probe beam right at the source of the large pressures generated. Several mechanisms are proposed to explain the source of these large signals, including surface-displacements, local refractive-index step-modulation, scatterer displacements, and photothermal mechanisms. We carefully model each of these mechanisms and predict the fraction of modulated light from each. Experimental measurements detect ~0.1% of the incident interrogation light is modulated and this is confirmed with theoretical modulation calculations. We provide experimental evidence that pressure-induced refractive-index step modulation and scatter position modulation may be highly significant modulation mechanisms. We also model theoretical limitations of signal-to-noise and discuss future system optimization opportunities.
Roger J. Zemp, W. Shi, and Parsin Haji Reza, "Signal mechanisms in photoacoustic remote sensing microscopy
(Conference Presentation)," Proc. SPIE 9708, Photons Plus Ultrasound: Imaging and Sensing 2016, 97082I (Presented at SPIE BiOS: February 17, 2016; Published: 27 April 2016); https://doi.org/10.1117/12.2211472.4828179376001.
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