Computational Nanomedicine and Nanotechnology by Renat R. Letfullin & Thomas F. George

Author:Renat R. Letfullin & Thomas F. George
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

Traditional knowledge of laser–nanoparticle interactions has necessitated specialized models for each case, dependent upon the laser pulse duration [2]. In the previous lecture we introduced a dual-temperature model for the ultrashort laser pulse mode, calculating electron and lattice subsystem temperatures. Pulses of longer duration are modeled using a uniform heating one-temperature model (OTM) derived in the previous lecture. The OTM is an appropriate approximation for pulse durations greatly exceeding the electron–phonon coupling time. This approximation is reasonable for particles sizes not much larger than the laser wavelength, which is completely applicable for the heating of nanoparticles.

Ultrashort pulses, specifically those in the femtosecond and picosecond ranges, impose several challenges in modeling material response (Slide 18.4). Free electrons with minimal capacity for heat are the first to absorb energy, rapidly attaining high temperatures and transferring thermal energy to the material lattice. These processes do not occur instantaneously: time must be allowed for the cooling of the electrons and the heating of the lattice. As shown in [4], the electron cooling and lattice heating have time delays on the order of femtoseconds and picoseconds, respectively. Ultrashort laser pulses end before the transfer of energy to the lattice is complete, requiring the two-temperature model in order to describe the further conversion of energy from electron excitation to heat within the lattice system.

Slide 18.4Introduction (continued)

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