Estimation of Dipole Moment from the Exterior Field of a Polarized Nanoparticle

Methods to estimate the dipole moment induced by an applied terahertz electric field on a semiconductor nanoparticle are studied, encompassing a first principle calculation involving charge integration and extraction from the exterior field intensity at a sample point. The latter approach requires very little post processing of data from field simulation based on coupling of charge transport equations to Maxwell's equations. When precaution is taken to avoid boundary of the domain for numerical simulation in the placement of the field sample point, very good match between the two methods are obtained. Validation of the quasi-static assumption in the field-charge interactions in the nanoparticle and the dominance of the dipole mode in excitation of polarization in nanoparticles of size less than 500 nm in the terahertz range was carried out by comparison of the computed exterior field intensity to a dipole field and the evaluation of the quadruple moment for the charge distribution in the particle.