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.

Terahertz tuning by core-shell nanoparticles irradiated by skew-cosh Gaussian lasers

“…´- This can be noticed that the results obtained in figure 5 and tables 1 and 2 are consistent with the observation made in [32,33,61,62] and the ponderomotive force experienced by the cylindrical core-shell NPs is higher in magnitude. Also, the observation of two resonance peaks obtained in case of the core-shell NPs is similar to the case of ordinary NPs, but the position of these peaks and hence the focus of the emitted THz radiation are different.…”

“…Also, the observation of two resonance peaks obtained in case of the core-shell NPs is similar to the case of ordinary NPs, but the position of these peaks and hence the focus of the emitted THz radiation are different. A comparison of the efficiency of simple NPs and core-shell NPs shows that a medium having simple NPs can be more efficient (10 times) than the medium having core-shell NPs for the same values of the laser index, radii of the NPs and inter-particle distance between the NPs [32,33,61,62]. But one of the foremost advantages of using core-shell NPs is that the released THz radiation can be easily tuned by changing radii of the core and shell which in case of simple NPs is not possible.…”

“…A unique type of nanoparticles among all is the 'core-shell nanoparticle' which is made up of more than one type of material, unlike usual nanoparticles. Recent studies have been performed on simple NPs in two different shapes, namely spherical and cylindrical, for the emission of THz radiation [32,33], but one of the limitations with simple NPs is that the emitted THz radiation cannot be tuned by changing the radii of the NPs while in the case of core-shell NPs this is intuitive that the emitted THz radiation can be modulated with the help of core and shell radii. The metallic shells have been found to be quite helpful in the biomedical areas because their optical properties make them perfect for inspecting the tissues [34].…”

Magnetic field enhanced terahertz generation from shape-dependent metallic nanoparticles

“…Extensive studies have been carried out to study the emission of THz fields using CNPs, such as nanorods, nanotubes and nanoribbons. Malik et al [22] used graphite nanocylinders in a host medium of argon gas for THz emission. Kumar et al [23] studied the effect of selffocusing and defocusing of Gaussian laser beam THz generation in a macroscopic dense array of anharmonic vertically aligned CNTs.…”

Excitation of tunable terahertz radiation from a mixture of nanoparticles in static magnetic field

“…Javan and Erdi [23] presented a model for generation of THz radiation via beat-wave mechanism using Gaussian laser beams in a spatially modulated medium of graphite nanoparticles. Malik et al [24] used graphite nanocylinders with hat-top beams whereas Kumar et al [25] studied the effect of self-focusing and defocusing of Gaussian laser beam THz generation in the macroscopic dense array of anharmonic vertically aligned CNTs.…”