Acoustic signals generated by laser-irradiated metal nanoparticles

Abstract

We present a physical model that explains several sequential stages of the conversion of optical to acoustical energy when irradiating diluted suspensions of metal nanoparticles with laser pulses. Optical absorption and scattering of a single particle driven by plasmon resonance interactions in an aqueous medium are considered. Thermal effects produced by laser-irradiated nanoparticles, dynamics of vapor bubble formation, and acoustic signals from expanding bubbles formed around heated nanoparticles are calculated. Stochastic features of the pressure magnitude emitted as a result of low-fluence irradiation of suspensions are also discussed. The probabilistic distribution of pressure magnitude from individual bubbles was found to obey Zipf's law for low concentrations of nanoparticles, while increasing their concentration brings the pressure magnitude distribution into conformance with the Gaussian law.

Biomedical photoacoustics beyond thermal expansion using triggered nanodroplet vaporization for contrast-enhanced imaging

“…Therefore, pulsed laser irradiation is used to activate this contrast agent, that is, to remotely trigger the phase transition of PFC. The PAnDs are vaporized when encapsulated plasmonic nanoparticles, such as gold nanorods, absorb electromagnetic energy from the laser, providing localized heating well over the required vaporization temperature of PFC 34 (steps 1-2 in Fig. 1b).…”

Numerical investigation on the dynamics of cavitation nanobubbles

“…Assuming that the excess light energy absorbed by the particle during the laser pulse is spent in boiling at the critical point of water, the initial radius of the bubble can be estimated as (Egerev et al 2009)…”

“…In the above equation, E cl is the internal energy of the liquid at the critical point, q cl is the critical density of the liquid, r abs represents the absorption cross section, F is the laser fluence, and F c is the critical laser fluence required to heat the nanoparticle to the boiling temperature T boil , which in the case of short laser pulses (v l s L \\R 2 np , where v l is the thermal diffusivity of the liquid) is given by Egerev et al (2009) …”

“…For long laser pulses v l s L [ [ R 2 np ; the expression for the critical laser fluence becomes (Egerev et al 2009)…”

“…Several theoretical studies have been conducted to investigate and model the boiling processes around laser-irradiated nanoparticles and microparticles (Schmid 2006;Volkov et al 2007). Two very recent publications (Egerev et al 2009;Gonzalez et al 2010) describe the formation of a cavitation bubble around a superheated nanoparticle in which an expression for the acoustic wave pressure as a function of laser pulse energy is given.…”