Scattering cross-sectional modulation in photoacoustic remote sensing microscopy.

Modeling and observations of large scattering cross-sectional modulations in absorbing optical scatterers due to a pulsed laser excitation are reported. Rapid laser-induced thermo-elastic expansion produces nontrivial perturbations to the local refractive indices. This mechanism forms the basis of a recent non-contact photoacoustic technique known as photoacoustic remote sensing microscopy. A time-evolution model is constructed and discussed, comparing it with existing planar models, time-independent models, and experiments. Fractional scattering cross-sectional modulations greater than 20 times that of the unperturbed particles are predicted and observed for the first time, to the best of our knowledge. A nonlinear acoustic enlargement effect is likewise predicted and observed. Implications of system and material properties are explored.