Numerical Analysis of Laser Induced Photothermal Effects using Colloidal Plasmonic Nanostructures

Colloidal noble metal (plasmonic) nanostructures are finding increasing use in a variety of photothermal applications that range from nanoparticle synthesis to bioimaging to medical therapy. In many applications, a pulsed laser is used to excite the plasmonic nanostructures at their plasmon resonant frequency, which results in a peak absorption of incident photons and highly localized (sub-wavelength) field enhancement. In addition to enabling efficient nanoscale heating from a remote source, the resonant heating wavelength can be tuned within the ultraviolet through nearinfrared spectrum by adjusting the geometry of the nanoparticle during synthesis. Following our previous work [1, 2], we present computational models to predict various photonic and thermo-fluidic aspects associated with nanosecond-pulsed, laser-heated colloidal metallic nanoparticles. We simulate energy conversion within different nanoparticle structures at plasmon resonance, heat transfer from the particle to the surrounding fluid and phase change of the fluid leading to homogenous bubble nucleation. We consider various nanoparticle geometries including nanorods, nanotori, nanorings and nanocages. We show that various process parameters such as the laser intensity, incident wavelength, polarization, pulse duration and the orientation and shape of the nanoparticles can be tuned to optimize the photothermal process. We discuss the utilization of such nanoparticles in photothermal applications involving bioimaging, drug delivery and therapy of malignant tumors.