Terahertz radiation due to random grating coupled surface plasmon polaritons

We report on terahertz (THz) radiation under electrical pumping from a degenerate semiconductor possessing an electron accumulation layer. In InN, the random grating formed by topographical defects provides high-efficiency coupling of surface plasmon polaritons supported by the accumulation layer to the THz emission. The principal emission band occupies the 2-6 THz spectral range. We establish a link between the shape of emission spectra and the structural factor of the random grating and show that the change of slope of power dependencies is characteristic for temperature-dependent plasmonic mechanisms. The super-linear rise of a THz emission intensity on applied electric power provides advantage of such materials in emission yield.Comment: 4 pages, 4 figure

Enhanced longitudinal mode spacing in blue-violet InGaN semiconductor laser

A novel explanation of observed enhanced longitudinal mode spacing in InGaN semiconductor lasers has been proposed. It has been demonstrated that e-h plasma oscillations, which can exist in the laser active layer at certain driving conditions, are responsible for mode clustering effect. The resonant excitation of the plasma oscillations occurs due to longitudinal mode beating. The separation of mode clusters is typically by an order of magnitude larger that the individual mode spacing.Comment: 3 pages, 2 figure

Laser assisted charge transfer reactions in slow ion–atom collisions: Coupled dressed quasimolecular‐states approach

This is the published version, also available here: http://dx.doi.org/10.1063/1.447712.Semiclassical coupled dressed quasimolecular states (DQMS) approaches are presented for the nonperturbative treatment of charge transferreactions at low collision velocities and high laser intensities. The DQMS are first obtained via the Floquet theory. The laser assisted collision process can then be treated as the electronic transitions among the DQMS driven by the nuclear motion only. The expansion of the total electronic wave function in a truncated DQMS basis results in a set of coupled a d i a b a t i c equations. The adiabatic DQMS and their associated quasienergies (depending parametrically upon the internuclear separation R) exhibit regions of avoided crossings, where the electronic transition probabilities are large due to strong radial couplings induced by the nuclear movement. By further transforming the a d i a b a t i c DQMS into an appropriate d i a b a t i c DQMS representation, defined via the vanishing of the aforementioned radial couplings, we obtain a new set of coupled d i a b a t i c equations which offer computational advantage. The method is illustrated by a case study of the laser assisted charge exchange process He+ ++H(1s)+ℏω→He+(n=2)+H+, in a two‐state approximation, for the velocity range from 1.5×105 to 2×107 cm/s and for the laser intensity in the range of 0.4 to 4.0 TW/cm2. Results of exact coupled diabatic DQMS calculations are presented along with several approximation calculations, using first order perturbation theory, the Magnus approximation, and the average cross section

Electron Correlations in an Electron Bilayer at Finite Temperature: Landau Damping of the Acoustic Plasmon

We report angle-resolved Raman scattering observations of the temperature dependent Landau damping of the acoustic plasmon in an electron bilayer system realised in a GaAs double quantum well structure. Corresponding calculations of the charge-density excitation spectrum of the electron bilayer using forms of the random phase approximation (RPA), and the static local field formalism of Singwi, Tosi, Land and Sj\"{o}lander (STLS) extended to incorporate non-zero electron temperature $T_{\rm e}$ and phenomenological damping, are also presented. The STLS calculations include details of the temperature dependence of the intra- and inter-layer local field factors and pair-correlation functions. Good agreement between experiment and the various theories is obtained for the acoustic plasmon energy and damping for $T_{\rm e} \lesssim T_{\rm F}/2$, the Fermi temperature. However, contrary to current expectations, all of the calculations show significant departures from our experimental data for $T_{\rm e} \gtrsim T_{\rm F}/2$. From this, we go on to demonstrate unambiguously that real local field factors fail to provide a physically accurate description of exchange correlation behaviour in low dimensional electron gases. Our results suggest instead that one must resort to a {\em{dynamical}} local field theory, characterised by a {\em{complex}} field factor to provide a more accurate description.Comment: 53 pages, 16 figure

Three Polarization Reflectometry Methods For Determination Of Optical Anisotropy.

Three novel methods for the determination of optical anisotropy are proposed and tested. The first, the special points method, may be applied to any uniaxially anisotropic medium and is based on the measurement of s- and p-polarized light reflectances under near-normal or grazing angles (or both) and of the Brewster angle. The second method is based on the use of the Azzam universal relationship between the Fresnel s- and p-reflection coefficients. For a flat surface and an isotropic medium, the Azzam combination of coefficients becomes zero and thus is independent of the incidence angle, whereas for a uniaxial or biaxial anisotropic sample it acquires a certain angular dependence, which may be used to determine the anisotropy of the sample. Finally, for those cases in which the anisotropy of the material of a film deposited on an isotropic substrate is itself of interest, a third method, the interference method, is suggested. This technique makes use of the different dependences of s- and p-polarized beam optical path-length changes on the variation of the angle of incidence.3765-7