133 research outputs found
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
Circular photon drag effect in bulk tellurium
The circular photon drag effect is observed in a bulk semiconductor. The
photocurrent caused by a transfer of both translational and angular momenta of
light to charge carriers is detected in tellurium in the mid-infrared frequency
range. Dependencies of the photocurrent on the light polarization and on the
incidence angle agree with the symmetry analysis of the circular photon drag
effect. Microscopic models of the effect are developed for both intra- and
inter-subband optical absorption in the valence band of tellurium. The shift
contribution to the circular photon drag current is calculated. An observed
decrease of the circular photon drag current with increase of the photon energy
is explained by the theory for inter-subband optical transitions. Theoretical
estimates of the circular photon drag current agree with the experimental data.Comment: 8 pages, 4 figure
Opto-Electronic Characterization of Three Dimensional Topological Insulators
We demonstrate that the terahertz/infrared radiation induced photogalvanic
effect, which is sensitive to the surface symmetry and scattering details, can
be applied to study the high frequency conductivity of the surface states in
(Bi1-xSbx)2Te3 based three dimensional (3D) topological insulators (TI). In
particular, measuring the polarization dependence of the photogalvanic current
and scanning with a micrometre sized beam spot across the sample, provides
access to (i) topographical inhomogeneity's in the electronic properties of the
surface states and (ii) the local domain orientation. An important advantage of
the proposed method is that it can be applied to study TIs at room temperature
and even in materials with a high electron density of bulk carriers.Comment: 6 pages, 4 figure
Helicity-dependent photocurrents in graphene layers excited by mid-infrared radiation of a CO-laser
We report the study of the helicity driven photocurrents in graphene excited
by mid-infrared light of a CO-laser. Illuminating an unbiased monolayer
sheet of graphene with circularly polarized radiation generates -- under
oblique incidence -- an electric current perpendicular to the plane of
incidence, whose sign is reversed by switching the radiation helicity. We show
that the current is caused by the interplay of the circular Hall effect
and the circular photogalvanic effect. Studying the frequency dependence of the
current in graphene layers grown on the SiC substrate we observe that the
current exhibits a resonance at frequencies matching the longitudinal optical
phonon in SiC
Fast detector of the ellipticity of infrared and terahertz radiation based on HgTe quantum well structures
We report a fast, room temperature detection scheme for the polarization
ellipticity of laser radiation, with a bandwidth that stretches from the
infrared to the terahertz range. The device consists of two elements, one in
front of the other, that detect the polarization ellipticity and the azimuthal
angle of the ellipse. The elements respectively utilise the circular
photogalvanic effect in a narrow gap semiconductor and the linear photogalvanic
effect in a bulk piezoelectric semiconductor. For the former we characterized
both a HgTe quantum well and bulk Te, and for the latter, bulk GaAs. In
contrast with optical methods our device is an easy to handle all-electric
approach, which we demonstrated by applying a large number of different lasers
from low power, continuous wave systems to high power, pulsed sources.Comment: 7 pages, 5 figure
Spin photocurrents and circular photon drag effect in (110)-grown quantum well structures
We report on the study of spin photocurrents in (110)-grown quantum well
structures. Investigated effects comprise the circular photogalvanic effect and
so far not observed circular photon drag effect. The experimental data can be
described by an analytical expression derived from a phenomenological theory. A
microscopic model of the circular photon drag effect is developed demonstrating
that the generated current has spin dependent origin.Comment: 6 pages, 3 figure
Исследование тепломассопереноса при воспламенении типичного лесного горючего материала в высокотемпературной среде
В работе рассмотрены основные закономерности тепломассопереноса в типичном лесном горючем материале (листе березы) с помощью экспериментального и численного моделирования. В обзоре литературы рассмотрены основные теоретические положения по данному вопросу. Глава объекты и методы исследования посвящена описанию основных приемов, применяемых в ходе изучения процессов тепломассопереноса. В главе результаты исследования сформулированы физическая и математическая модель процесса, представлены полученные результаты и сделаны выводы об особенностях листа березы как лесного горючего материала.The paper discusses the main laws of heat and mass transfer in a typical forest fuel material (birch leaf) using experimental and numerical modeling. The review of the literature describes the main theoretical principles on this issue. The chapter objects and research methods is devoted to the description of the main techniques used in the study of heat and mass transfer processes. Physical and numerical models of the process and obtained results are presented. Conclusions are drawn about the features of the birch leaf as a forest combustible material
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