Hat-Top Beams for Generating Tunable THz Radiations Using a Medium of Conducting Nanocylinders

Abstract

There are a large number of studies for terahertz (THz) radiation generation, but tunable THz sources are still a challenge since it is difficult to tune frequency, focus and intensity of the radiation simultaneously. The present work proposes the THz generation by the interaction of two hat-top laser beams with a host medium of argon gas containing graphite nanocylinders, as these beams result in highly nonlinear interaction because of a smooth dip in their peak intensity and a fast rise and fall in the overall intensity pattern. Such an interaction produces nonlinear current (6.7 × 108 A/m2) because of the electron cloud of the nanocylinders, which can be modulated by the laser and medium properties for realizing tunable THz radiation. The orientation of basal planes of nanocylinders is shown to be important for this mechanism, though it may be challenging for the experimentalists. The resonant excitation takes place when the plasmon frequency matches the beating frequency of the laser beams, and in the proposed mechanism one can have longitudinal surface plasmon resonance (~12 THz) and transverse surface plasmon resonance (~40 THz), leading to frequency-tunable THz radiation. The role of height and inter particle distance between the adjacent nanocylinders on the THz field amplitude and the efficiency of the mechanism is uncovered by controlling the aspect ratio in the nanocylinders. For example, reducing the inter particle distance from 180 nm to 60 nm leads to the enhancement of THz field from 1 × 108 V/m to 5.48 × 108 V/m. The profile of the emitted THz radiation is investigated in detail under the effect of various parameters in order to prove the practicality of the proposal. The proposed design and mechanism would be attractive for electromagnetic and communication societies which are dealing with millimeter-waves and THz components in addition to its medical application.