Abstract:In medical applications of laser and nanotechnology to diagnosis and treat cancer or microorganisms, understanding of lased-induced photothermal (PT) and accompanied phenomena around nanoparticles are crucial for optimization and bringing this promising technology to bedside. We analyzed the main PT-based effects in and around gold nanoparticles under action of short (nano-, pico-, and femtosecond) laser pulses with focus on photoacoustic effects due to the thermal expansion of nanoparticles and liquid around them, thermal protein denaturation, explosive liquid vaporization, melting and evaporation of nanoparticle, optical breakdown initiated by nanoparticles and accompanied to shock waves and explosion (fragmentation) of gold nanoparticles. Characteristic parameters for these processes such as the temperature and pressures levels, and laser intensity thresholds among others are summarized to provide basis for comparison of different mechanisms of selective nanophotothermolysis and diagnostics of different targets (e.g., cancer cells, bacteria, viruses).

The phenomenon of optical (laser) radiation heating of nanoparticles (NP) is important for applications in laser processing of NPs (laser induced transformation in NP size, shape and structure), light-to-thermal energy conversion and nanoenergy, laser nanomedicine, thermal catalysis, and so forth. It is essential to theoretically describe the temporal and spatial-temporal behavior of the NPs and the medium temperature for the analysis of experimental results and for the theoretical prediction of the unknown dependencies and new effects. Analytical and computer descriptions of heating, melting of a single NP under the action of CW and pulsed optical (laser) radiation and NP cooling after the termination of radiation action is carried out. An analytical model developed for the description of NP heating, heat dissipation and exchange with an ambience and cooling has been examined, and its accuracy and applicability has been estimated and established.

Results of experimental and computational investigations devoted to energy transfer mechanisms and X-ray conversion efficiency in laser-produced plasma are presented and discussed. The layers of different thicknesses and diameters deposited on the plane mylar substrate were irradiated by the focused beam of Nd:glass laser. Spectrally, temporally, and spatially resolved measurements of soft X-ray emission have been carried out at power densities of 1013-1014 W/cm2. The conditions of “re-emission” zone formation have been established. Radiative heat conductivity is shown to be the important energy transfer mechanism in the experimental conditions under investigation.