Comparative Study on the Uniform Energy Deposition Achievable via Optimized Plasmonic Nanoresonator Distributions

Abstract

Plasmonic nanoresonators of core–shell composition and nanorod shape were optimized to tune their absorption cross-section maximum to the central wavelength of a short laser pulse. The number density distribution of randomly located nanoresonators along a laser pulse-length scaled target was numerically optimized to maximize the absorptance with the criterion of minimal absorption difference between neighboring layers illuminated by two counter-propagating laser pulses. Wide Gaussian number density distribution of core–shell nanoparticles and nanorods enabled to improve the absorptance with low standard deviation; however, the energy deposited until the overlap of the two laser pulses exhibited a considerable standard deviation. Successive adjustment resulted in narrower Gaussian number density distributions that made it possible to ensure almost uniform distribution of the deposited energy integrated until the maximal overlap of the two laser pulses. While for core–shell nanoparticles the standard deviation of absorptance could be preserved, for the nanorods it was compromised. Considering the larger and polarization independent absorption cross-section as well as the simultaneously achievable smaller standard deviation of absorptance and deposited energy distribution, the core–shell nanoparticles outperform the nanorods both in optimized and adjusted nanoresonator distributions. Exception is the standard deviation of deposited energy distribution considered for the complete layers that is smaller in the adjusted nanorod distribution. Optimization of both nanoresonator distributions has potential applications, where efficient and uniform energy deposition is crucial, including biomedical applications, phase transitions, and even fusion.

Kinetic model of resonant nanoantennas in polymer for laser induced fusion

“…Simulation studies using the COMSOL Multi-physics Finite Element Method (FEM) package with many parameters found Frontiers in Physics frontiersin.org absorption coefficient between 256 cm −1 and 1,142 cm −1 for nanorod antennas [14]. By varying the density distribution of implanted nanoantennas one could achieve almost uniform integrated energy absorption at a given overlapping time of 240 fs for two counterpropagating 120 fs laser pulses [14,27]. The beam intensity utilized was I = 4 • 10 15 W/cm 2 so that the plasmonic nanoantennas are not destroyed before the laser pulse passes.…”

“…Conduction band electrons follow the oscillating field, which results in nearfield enhancement [14], however in the process of repeated excitation the gold nanoparticles get ionized [28]. This leads to electron spill out effects [29].…”

“…Here we study the idea of layered flat target fuel with embedded nanorod antennas, that regulate laser light absorption to enforce simultaneous ignition. We plan a seven-layer flat target with layer-dependent nanorod densities [14][15][16]. In order to prepare such a layered target, the ignition fuel (e.g., deuterium, D, tritium, T, or other nuclei for fusion) are embedded into a hard thin polymer material of seven, 3 μm thick layers.…”

With Nanoplasmonics towards Fusion

“…The theory behind hoping for an enhancement of energy density due to plasmonics requires extended computer simulations on the motion of electrons on the Au nanoantennas of resonant size and various shapes. Although in the experiment, we are using cylindrical shapes, other shapes and metals sometimes promise a higher value of near field enhancement [8]. Theoretically, near-field enhancement (NFE) factors in the order of 100 can be reached, meaning an energy density enhancement of 10 4 in near atomic layers, up to cca.…”

“…For this purpose, one has to regulate the energy deposition in the fusion target. The implanted nanoantennas, with an adequately designed density distribution, also help to reach this goal [8,18].…”