Photoacoustic signal enhancements from gold nano-colloidal suspensions excited by a pair of time-delayed femtosecond pulses

摘要

Photoacoustic signal enhancements were observed with a pair of time-delayedfemtosecond pulses upon excitation of gold nanosphere colloidal suspension. Asystematic experimental investigation of photoacoustic intensity within thedelay time, t = 0 to 15 ns, was carried out. The results revealed a significantenhancement factor of ~2 when the pre-pulse energy is 20-30% of the totalenergy. Pre-pulse and main pulse energy ratios, E(1)p-pol. :E(2)s-pol. werevaried to determine the optimal ratio that yields to maximum photoacousticsignal enhancement. This enhancement was ascribed to the initial stage ofthermalization and bubble generation in the nanosecond time scale. Pre-pulsescattering intensity measurements and numerical finite-difference time-domaincalculations were performed to reveal dynamics and light field enchancement,respectively.