27 research outputs found
Oscillation regimes of a solid-state ring laser with active beat note stabilization : from a chaotic device to a ring laser gyroscope
We report experimental and theoretical study of a rotating diode-pumped
Nd-YAG ring laser with active beat note stabilization. Our experimental setup
is described in the usual Maxwell-Bloch formalism. We analytically derive a
stability condition and some frequency response characteristics for the
solid-state ring laser gyroscope, illustrating the important role of mode
coupling effects on the dynamics of such a device. Experimental data are
presented and compared with the theory on the basis of realistic laser
parameters, showing a very good agreement. Our results illustrate the duality
between the very rich non linear dynamics of the diode-pumped solid-state ring
laser (including chaotic behavior) and the possibility to obtain a very stable
beat note, resulting in a potentially new kind of rotation sensor
Авіаційна навігаційна система на основі поляриметричних технологій
The paper deals with questions of developing polarimetric navigation method for determiningaircraft’s coordinates. This method, potentially, can increase the accuracy and sensitivity of navigationparameters determination. The paper also deals with existing methods and systems for determining aircraft’snavigation parameters and proposed polarimetric method. Also offered block diagrams of the onboardand ground polarimetric device. In article were given result of the mathematical modeling of measuringchannelРассмотрен вопрос разработки поляриметрического навигационного метода для определения координат воздушного судна. Этот метод, потенциально, позволяет повысить точность и чувствительность определения навигационных параметров. Рассмотрены существующие методы и системы и предложен поляриметрический методдля определения навигационных параметров летательного аппарата. Предложена блок-схема бортового и наземного поляриметрического устройства. Приведены результаты математического моделирования измерительного каналаРозглянуто питання розроблення поляриметричного навігаційного методу для визначення координат повітряного судна. Цей метод, потенційно, дозволяє підвищити точність та чутливість визначення навігаційних параметрів. Розглянуто існуючі методи і системи та запропоновано поляриметричний метод для визначення навігаційних параметрів літального апарату. Запропоновано блок-схему бортового і наземного поляриметричного пристрою. Приведено результати математичного моделювання вимірювального канал
A ring laser gyroscope without lock-in phenomenon
We theoretically and numerically study the effect of backscattering on
rotating ring lasers by employing the Maxwell-Bloch equations. We show that
frequency shifts due to the Sagnac effect incorporating the effect of
backscattering can be observed without lock-in phenomenon, if the strength of
backscattering originating in the bumps of the refractive index is larger than
a certain value. It is also shown that the experimental results corresponding
to the theoretical ones can actually be obtained by using a semiconductor
fiber-optic ring laser gyroscope.Comment: 9 pages, 6figure
Ultra-shallow quantum dots in an undoped GaAs/AlGaAs 2D electron gas
We report quantum dots fabricated on very shallow 2-dimensional electron
gases, only 30 nm below the surface, in undoped GaAs/AlGaAs heterostructures
grown by molecular beam epitaxy. Due to the absence of dopants, an improvement
of more than one order of magnitude in mobility (at 2E11 /cm^2) with respect to
doped heterostructures with similar depths is observed. These undoped wafers
can easily be gated with surface metallic gates patterned by e-beam
lithography, as demonstrated here from single-level transport through a quantum
dot showing large charging energies (up to 1.75 meV) and excited state energies
(up to 0.5 meV).Comment: 4 pages, 4 figures; added figures, references, equations, and text;
results/conclusions otherwise unchange
Extreme sensitivity of the spin-splitting and 0.7 anomaly to confining potential in one-dimensional nanoelectronic devices
Quantum point contacts (QPCs) have shown promise as nanoscale spin-selective
components for spintronic applications and are of fundamental interest in the
study of electron many-body effects such as the 0.7 x 2e^2/h anomaly. We report
on the dependence of the 1D Lande g-factor g* and 0.7 anomaly on electron
density and confinement in QPCs with two different top-gate architectures. We
obtain g* values up to 2.8 for the lowest 1D subband, significantly exceeding
previous in-plane g-factor values in AlGaAs/GaAs QPCs, and approaching that in
InGaAs/InP QPCs. We show that g* is highly sensitive to confinement potential,
particularly for the lowest 1D subband. This suggests careful management of the
QPC's confinement potential may enable the high g* desirable for spintronic
applications without resorting to narrow-gap materials such as InAs or InSb.
The 0.7 anomaly and zero-bias peak are also highly sensitive to confining
potential, explaining the conflicting density dependencies of the 0.7 anomaly
in the literature.Comment: 23 pages, 7 figure
Gigahertz single-electron pumping mediated by parasitic states
In quantum metrology, semiconductor single-electron pumps are used to generate accurate electric currents with the ultimate goal of implementing the emerging quantum standard of the ampere. Pumps based on electrostatically defined tunable quantum dots (QDs) have thus far shown the most promising performance in combining fast and accurate charge transfer. However, at frequencies exceeding approximately 1 GHz the accuracy typically decreases. Recently, hybrid pumps based on QDs coupled to trap states have led to increased transfer rates due to tighter electrostatic confinement. Here, we operate a hybrid electron pump in silicon obtained by coupling a QD to multiple parasitic states and achieve robust current quantization up to a few gigahertz. We show that the fidelity of the electron capture depends on the sequence in which the parasitic states become available for loading, resulting in distinctive frequency-dependent features in the pumped current
Spin dynamics in semiconductors
This article reviews the current status of spin dynamics in semiconductors
which has achieved a lot of progress in the past years due to the fast growing
field of semiconductor spintronics. The primary focus is the theoretical and
experimental developments of spin relaxation and dephasing in both spin
precession in time domain and spin diffusion and transport in spacial domain. A
fully microscopic many-body investigation on spin dynamics based on the kinetic
spin Bloch equation approach is reviewed comprehensively.Comment: a review article with 193 pages and 1103 references. To be published
in Physics Reports