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

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.

Electron Bernstein wave aided heating of collisional nanocluster plasma by nonlinear interactions of two super-Gaussian laser beams

In this present theoretical study, we investigate electron Bernstein wave (EBW) aided collisional nanocluster plasma heating by nonlinear interaction of two super-Gaussian laser beams. The interactions of laser beams electric field profiles with electronic clouds of nanoclusters cause the beat wave. The nonlinear ponderomotive force is generated through the beat wave. There may be good potential to excite the EBW aiding cluster plasma to lead electron heating via cyclotron damping of the Bernstein wave. An analytical scheme is proposed for the anomalous heating and evolution of electron temperature by using this mechanism. Graphical discussions were promised to achieve extreme heating rate via the spatial shape of super-Gaussian laser beams and the resonance condition of beat wave to surface plasmon frequency. The heating is controlled by tuning the laser beam width, mode index, collisional frequency, clustered radius, and density.

A Plasmon Modulator by Directly Controlling the Couple of Photon and Electron

As a strong couple mode of photon and electron collective oscillation, the movement of an electron can affect the collective plasmon behaviors efficiently. In this paper, we proposed a novel method for modulating the plasmon by directly controlling the movement of the electron but independent of the properties of the medium. This method is demonstrated by a hybrid graphene-dielectric-interdigital electrode structure in the mid-infrared range. It is possible to regulate the confinement of the graphene carrier and stimulate the plasmon in real-time by using the potential wells created by interdigital electrodes. Furthermore, the plasmon frequency can also be modulated utilizing changing the confined area and the density of the carrier. As a result. the frequency has been tuned over a range of ~ 33 cm−1 by applying voltage, and the maximum extinction ratio we measured is 8%. Due to the movement of the electron can also be driven optically, these findings may define a new approach to the all-optical modulator with low pump power.

Effect of Lanthanum Substrates on the Structural, Optical and Electrical Properties of Copper Selenide Thin Films Designed for 5G Technologies

In this work, copper selenide thin films coated onto glass and transparent lanthanum substrates are studied. The (glass, La)/CuSe thin films which are prepared by the thermal evaporation technique under a vacuum pressure of 10− 5 mbar are structurally, morphologically, optically, dielectrically and electrically characterized. Lanthanum substrates improved the crystallinity by increasing the crystallite size and decreasing both of the microstrains and defect density of copper selenide. La substrates redshifts the energy band gap and doubled the dielectric constant values. In addition, employing Drude-Lorentz approaches for optical conduction to fit the dielectric constant provided information about the effects of La substrates on the drift mobility, plasmon frequency, free carrier density and scattering times at femtosecond level. The drift mobility increased and the plasmon frequency range is modified when La substrates are used. Verifying impedance spectroscopy test in the microwave frequency domain have shown that the La(gate)/CuSe/Ag (source) transistors can be employed as band pass filter suitable for 5G technologies. The microwave cutoff frequency reached ~ 5.0 GHz at a notch frequency of 2.80 GHz of the La/CuSe/Ag highpass filters.

DISPERSION RELATIONS IN BILAYER GRAPHENE AT FINITE TEMPERATURE

It is well-known that material technology is considered as one of the scientific fields attracting a lot of attention from scientists. Recently, graphene, a perfect two-dimensional structure, has attracted a large amount of interest from researchers due to its unique properties and possible applications in a variety of technological fields. The dispersion relations in graphene demonstrate that this material can be used to create plasmonic devices with potentially more features and less energy consumption than recent semiconductors. This paper calculates the dispersion relations in a bilayer graphene structure at finite temperatures using the random-phase approximation. The numerical results show that as temperature increases from zero, the plasmon frequency decreases slightly near the Dirac points and then increases noticeably. In large wave vector regions, the plasmon frequency behaves as an increasing function of temperature. The contribution of carrier density to plasmon frequency in the bilayer graphene system diminishes when temperature effects are taken into account. We observed that temperature significantly affects the dispersion relations in bilayer graphene systems; therefore, this factor should not be neglected in efforts to improve models or in comparisons with experimental results.

All-optical switching of an epsilon-near-zero plasmon resonance in indium tin oxide

Nonlinear optical devices and their implementation into modern nanophotonic architectures are constrained by their usually moderate nonlinear response. Recently, epsilon-near-zero (ENZ) materials have been found to have a strong optical nonlinearity, which can be enhanced through the use of cavities or nano-structuring. Here, we study the pump dependent properties of the plasmon resonance in the ENZ region in a thin layer of indium tin oxide (ITO). Exciting this mode using the Kretschmann-Raether configuration, we study reflection switching properties of a 60 nm layer close to the resonant plasmon frequency. We demonstrate a thermal switching mechanism, which results in a shift in the plasmon resonance frequency of 20 THz for a TM pump intensity of 70 GW cm−2. For degenerate pump and probe frequencies, we highlight an additional two-beam coupling contribution, not previously isolated in ENZ nonlinear optics studies, which leads to an overall pump induced change in reflection from 1% to 45%.

Heavy quark diffusion in an overoccupied gluon plasma

We extract the heavy-quark diffusion coefficient κ and the resulting momentum broadening 〈p2〉 in a far-from-equilibrium non-Abelian plasma. We find several features in the time dependence of the momentum broadening: a short initial rapid growth of 〈p2〉, followed by linear growth with time due to Langevin-type dynamics and damped oscillations around this growth at the plasmon frequency. We show that these novel oscillations are not easily explained using perturbative techniques but result from an excess of gluons at low momenta. These oscillation are therefore a gauge invariant confirmation of the infrared enhancement we had previously observed in gauge-fixed correlation functions. We argue that the kinetic theory description of such systems becomes less reliable in the presence of this IR enhancement.

Improvement of Optical Extinction by Various Wideband Dielectrics with Ag and Aunanoparticle on Metal-dielectric-semiconductor Structure in Solar Cell

Background: In this article, photonic extinction performance of Metal Dielectric Semiconductor (MDS) nanostructure has been improved by noble metallic nanosphere such as gold, silver and copper into various wideband dielectrics like silicon di-oxide, aluminum oxide and silicon nitride. Methods: Presently, Plasmonics gives very much interest and closely involves in the main domains of nanophotonics that can control of optical fields at the nanoscale level as well as it can concentrate and enhance the electromagnetic field on the nanometer scale especially in metal dielectric semiconductor (MDS) nanostructure. Results: In plasmonics, noble metals used as nanoparticle where density of electron gas which oscillates at surface Plasmon frequency so we investigate impact of various wideband dielectrics with nanoparticle size for enhancement of extinction in terms of absorption and scattering by using surface Plasmon resonance. Conclusion: At Plasmonic resonance the efficiency will be maximum. If the size of the metallic nanosphere increases, initially the efficiency increases up to a certain wavelength then it becomes sharply decreased.

All-Optical Switching of an Epsilon-Near-Zero Plasmon in ITO

Nonlinear optical devices and their implementation into modern nanophotonic architectures are constrained by their usually moderate nonlinear response. Recently, epsilon-near-zero (ENZ) materials have been found to have a strong optical nonlinearity, which can be enhanced through the use of cavities or nano-structuring. Here, we study the pump dependent properties of the plasmon resonance in the ENZ region in a thin layer of thin indium tin oxide (ITO). Exciting this mode using the Kretschmann-Raether configuration, we study reflection switching properties of a 60nm layer close to the resonant plasmon frequency. We demonstrate the thermal switching mechanism, which results in a shift in the plasmon resonance frequency of 20THz for a TM pump intensity of 75GW/cm2. For degenerate pump and probe frequencies, we highlight an additional coherent contribution, not previously isolated in ENZ nonlinear optics studies, which leads to an overall pump induced change in reflection from 1% to 45%.