[en] A large amplitude surface plasma wave (SPW), propagating over a semiconductor-free space interface, is susceptible to filamentation instability. A small perturbation in the amplitude of the SPW across the direction of propagation exerts a ponderomotive force on free electrons and holes, causing spatial modulation in free carrier density and hence the effective permittivity ε_eff of the semiconductor. The regions with higher ε_eff attract more power from the nieghborhood, leading to the growth of the perturbation. The growth rate increases with the intensity of the surface wave. It decreases with the frequency of the SPW

[en] A relativistic electron beam propagating in a plasma cylinder excites a surface plasma wave (SPW) via the Cerenkov interaction. The wave frequency decreases with beam velocity. The growth rate, however, initially increases with frequency ω, attains a maximum, and then falls off due to the localization of the SPW near the surface. For typical parameters, maximum growth occurs at ω/ω_P≅0.36, where ω_P is the plasma frequency. With the increase in the radius of the thin plasma cylinder, the optimum growth rate increases in magnitude. The annular beam propagating outside the plasma cylinder excites the SPW with larger growth rate for the same beam current and the beam radius r_b=1.02a, where a is the radius of the thin plasma cylinder.

[en] We investigate a terahertz (THz) plasmonic waveguide using periodically arranged tilted pillars and control the propagation properties of the guided modes with the bending of pillars. A metal surface approximated as a perfect electrical conductor at terahertz frequencies is periodically corrugated with sub-wavelength scale tilted pillars thereby forming a plasmonic waveguide. The tilted pillars plasmonic waveguide supports highly confined guided terahertz modes at specific frequencies depending upon the pillar dimensions. We confirm the propagation of terahertz modes through a semi-analytical model that we employ specifically for our geometry. We observe that the propagation properties of the terahertz modes can be controlled by changing the bending of the pillars. We have examined in detail, the propagation properties of the guided modes for different angles and direction through which the pillars are tilted. We further examine terahertz waveguides comprising of pillars with increasing height and investigate their ability in confining terahertz waves at a certain position where the resonant frequency of a pillar matches with the incident frequency. (paper)

[en] Mg_0.9Mn_0.1In_xFe_2-x O₄ (x = 0.1 and 0.2) and Mg_0.9Mn_0.1Al_yFe_2-y O₄ (y = 0.1, 0.5 and 0.7) ferrites, with improved initial permeability and extremely low relative loss factor (RLF), were synthesized by the citrate precursor technique. Structural studies were made by using the x-ray diffraction technique and scanning electron microscopy (SEM), which confirm the formation of single-phase spinel structure. The size of the particle was of the order of ∼0.5 μm for the samples sintered at 1200 ⁰C, which is smaller than that obtained for ferrite powders by the conventional ceramic method. The magnetic properties such as initial permeability and RLF with frequency, in the range 0.1-20 MHz, at different temperatures have been investigated. Initial permeability (μ_i) attains a very high value, 17342, for the In³⁺ doped ferrite series and for the Al³⁺ doped ferrite series the maximum value is 3785. The RLF was found to have low values and is of the order of 10^-5-10^-4 in the frequency range 0.1-20 MHz. In addition to this, an increase in the value of μ_i was observed with the rise in the temperature for all the series of ferrites.

[en] We discuss the excitation of dual toroidal dipolar resonances in a bilayer terahertz metamaterial configuration and examine their near field coupling induced modulation. The study is focused on the interaction and modulation between toroidal resonances excited in two layers of a bilayer system. The rotation of the symmetric circular split ring of the top layer resonator with respect to the bottom one, causes the dual resonances to modulate and ultimately switching into a single toroidal resonance. The strong near field coupled modulation is observed when both the resonator layers are placed in close proximity. A Lagrangian approach is suggested to understand the underlying mechanism of the coupled toroidal resonances. The increase in strength of the toroidal dipolar resonance on adding two layers is suggested based upon the quality factors of the resonances. Such a study enables the design of toroidal photonics devices with high quality factors and improved light–matter interaction. (paper)

[en] A large-amplitude surface plasma wave (SPW) over a metal-vacuum interface Ohmically heats the electrons and undergoes nonlinear absorption. The attenuation rate increases with the local SPW amplitude. The enhanced electron temperature leads to stronger thermionic emission of electrons. At typical Nd:glass laser intensity I_L=7 GW/cm², if one takes the amplitude of the SPW to be ≅6 times the amplitude of the laser, one obtains the thermionic electron emission current density J=200 A/cm². However, the emission current density decreases with propagation distance at a much faster rate than the SPW amplitude and electron temperature

[en] We demonstrate that a one-dimensional periodically corrugated metal film can be used to create planar terahertz (THz) waveguides. The periodic corrugation is in the form of rectangular blind holes (i.e. holes that do not completely perforate the metal film) that are fabricated using a multilayer construction. The approach allows for the creation of structures in which the hole depth can be more than four times the hole width. This is necessary to achieve tightly confined THz guided-wave modes. We find that the modes can be modeled using an effective cavity resonance model and that the mode properties depend sensitively on the depth of corrugation. We use numerical simulations to validate the experimental results. We also highlight the differences between simulations that incorporate idealized input parameters and our experimental measurements. Using these data, we fabricate and characterize a Y-splitter to demonstrate the utility of this approach.

[en] A surface plasma wave (SPW) of frequency ω₁ and wave number k₁ propagating along a metal-free space boundary exerts a ponderomotive force on the free electrons, creating an electron density perturbation at frequency 2ω₁. When a laser of frequency ω₂ and wave number k₂ is incident at a suitable angle on the metal surface, it gives rise to the oscillatory velocity of electrons at frequency ω₂. This oscillatory velocity couples with the density perturbation to generate a nonlinear current at frequency 2ω₁+ω₂. The nonlinear current derives a radiating wave under suitable conditions. By measuring the amplitude of the radiating wave, the SPW field can be probed

[en] A surface plasma wave (SPW), propagating along a metal surface, embedded with regularly arranged nanoparticles, undergoes surface enhanced Raman scattering from molecules adsorbed over the particles. The enhancement in the scattered signal depends on the shape and dielectric constant of the metallic particles. The scattered signal can be detected above the metal surface as a space wave if the particles have a periodic arrangement with wave number q such that ω_R > (k_S - q)c, where ω_R is the frequency of the scattered signal and k_S is the wave number of SPW

[en] In this article, we investigate terahertz surface plasmons propagation in a planar waveguide comprising asymmetric resonators placed in close proximity. The waveguide is designed to support surface plasmon polaritons at two distinct terahertz frequencies, ω ₁ and ω ₂, which are near to each other. This is accomplished by carefully designing the unit cell comprising of two resonators with slightly different sizes. The resonators in the form of rectangular apertures are placed along the transverse direction in the near field regime. We observe an absorption window surrounded by two transmission resonances which are coupled to each other. As the resonators are moved apart, we observe a switching from the coupled to an uncoupled resonance state. The absorption window can be tuned by changing the resonance frequency of the resonators, which depends upon its structural parameters. We have employed a theoretical model to understand the coupling mechanism between the resonators and the dispersive behavior resulting in the absorption window. The proposed study is significant in the construction of planar terahertz components such as slow lights systems, buffers, etc, where strongly dispersive mediums play a vital role. (paper)