Total Polarisation Conversion in Two-dimensional Electron System under Cyclotron Resonance Conditions

The polarisation conversion of a linear polarised electromagnetic wave incident onto a two-dimensional (2D) electron system at an angle is theoretically studied. We consider the 2D system located at the interface between two dielectric media with different dielectric constants. An external dc magnetic field is assumed to be directed along the normal to the 2D electron layer. In such a configuration the cyclotron-polaritons (CPs) in 2D electron system can be excited with the frequencies in the vicinity of the cyclotron frequency. Under the CPs excitation the resonance polarisation conversion of electromagnetic wave greatly increases in the system. In the absence of the electron scattering in 2D system, the polarisation conversion reaches 100% at a certain value of the angle of incidence which is more than the total reflection angle. Extremely high polarisation conversion takes place in a quite wide range of variation of the angle of incidence. High polarisation conversion efficiency (above 80%) remains when the actual electron scattering in the 2D system on GsAs is taken into account. The considered phenomena may be taken up in polarisation spectroscopy of 2D electron systems.Comment: 7 pages, 5 Postscript figure

R A P I D C O M M U N I C AT I O N A structure for enhanced terahertz emission from a photoexcited semiconductor surface

Abstract A structure that can provide enhancement of terahertz emission from a semiconductor surface excited with femtosecond laser pulses is proposed. The structure consists of a semiconductor layer on a Si substrate with metal coating on the upper surface of the layer and a Si lens attached to the bottom of the substrate. The semiconductor is excited through a hole in the coating and emits terahertz radiation through the substrate lens. We demonstrate theoretically that the proposed structure can increase the terahertz yield by orders of magnitude as compared to the previously used schemes of terahertz emission from a semiconductor surface

Relativistic effects in radar detection of ionization fronts produced by ultra-high energy cosmic rays

We revisit the radar echo technique as an approach to detect ultra-high energy cosmic rays (UHECR). The UHECR extensive air showers generate disk-like ionization fronts propagating with a relativistic velocity and creating fast decaying plasma. We study the reflection of a radio wave, such as the one from a radar transmitter or commercial radio and TV station, from the relativistic ionization front. The reflected wave will be frequency upshifted due to the relativistic Doppler effect and propagate almost normally to the front due to relativistic aberration. The amplitude of the reflected wave depends strongly on the front velocity and parameters (density, collision frequency) of the plasma behind the front. We develop a theory that allows one to find the reflected wave. Using this theory and typical parameters of extensive air showers, we discuss the feasibility of UHECR detection. © 2010 Elsevier B.V. All rights reserved

The no-reflection regime of radar detection of cosmic ray air showers

© 2015 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft. The ionization front of a cosmic ray air shower propagates in the atmosphere with almost the speed of light in vacuum, i.e., faster than a radio wave in the air. There can be no reflection of a radar signal from such a front. Instead, an additional transmitted wave, which travels behind the front in the backward direction, is generated. We study the frequencies, propagation directions, and amplitudes for the waves excited at the front and discuss their use for radar detection of air showers

Prospects for radar detection of cosmic ray air showers with medium-frequency radio waves

We show that the highly relativistic motion of an extensive air shower allows one to increase the wavelength of the radar signal above its transverse size without giving rise to signal scattering. This increases the efficiency of detection due to an increase in the reflection from the shower and a lower level of sky noise in the frequency range of the reflected signal. © IOP Publishing and Deutsche Physikalische Gesellschaft

A structure for enhanced terahertz emission from a photoexcited semiconductor surface

A structure that can provide enhancement of terahertz emission from a semiconductor surface excited with femtosecond laser pulses is proposed. The structure consists of a semiconductor layer on a Si substrate with metal coating on the upper surface of the layer and a Si lens attached to the bottom of the substrate. The semiconductor is excited through a hole in the coating and emits terahertz radiation through the substrate lens. We demonstrate theoretically that the proposed structure can increase the terahertz yield by orders of magnitude as compared to the previously used schemes of terahertz emission from a semiconductor surface