Vasily V. Klimov

Acoustic signals generated by laser-irradiated metal nanoparticles

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 Zipfs law for low concentrations of nanoparticles, while increasing their concentration brings the pressure magnitude distribution into conformance with the Gaussian law.

Pulsed optoacoustic interaction in suspension of gold nanoparticles: detection sensitivity based on laser-induced nanobubbles

The sensitivity of optoacoustic (OA) detection in diluted suspensions of gold nanoparticles under irradiation with nanosecond laser pulses was studied as a function of incident laser fluence. The range of moderate values of the laser fluence from 20 mJ/cm2 to 2 J/cm2 was studied theoretically and experimentally. Under these laser fluences, the usual thermoelastic mechanism of OA generation faces competition from laser-induced cavitation, a statistical process, which leads to considerable fluctuations of the acoustic response from one laser pulse to another. Analytical expressions for the statistical characteristics of the acoustic signal were obtained. A simulation of the statistical characteristics of the cavitation contribution to the signal was performed using the method of Monte Carlo. The experiment utilized the second harmonic pulses (532 nm) of an Nd:YAG laser to irradiate samples of water suspensions of spherical gold nanoparticles (NPs). A series of laser pulses each having from 100 to 2000 pulses were used to iradiate the samples. The statistical rank distributions of the magnitudes of optoacoustic signals recorded by a wide band ultrasonic transducer attached to the measurement cell were used as a tool for sensitive detection of a low concentration of the gold nanoparticles in water.

Tuning spontaneous radiation of chiral molecules by asymmetric chiral nanoparticles

We have obtained analytical expressions for the radiative decay rate of the spontaneous emission of a chiral molecule located near a dielectric spherical particle with a chiral nonconcentric spherical shell made of a bi-isotropic material. Our numerical and graphical analyses show that material composition, thickness and degree of non-concentricity of the shell can influence significantly the spontaneous radiation of the chiral molecule. In particular, the radiative decay rates can differ in orders of magnitude for a chiral molecule located near the thin and thick parts of a nonconcentric shell as well as near a concentric shell made of chiral metamaterial. We also find that the radiative decay rates of the right and left chiral molecule enantiomers located near a nanoparticle with a chiral metamaterial shell can differ pronouncedly from each other. Our findings therefore suggest a way to tune the spontaneous emission of chiral molecules by varying the material composition, thickness and degree of non-concentricity of the shell in the nearby composite nanoparticle and also to enhance the chirality selection of chiral molecules in racemic mixtures.