397 research outputs found
Generation of microwave radiation by nonlinear interaction of a high-power, high-repetition rate, 1064-nm laser in KTP crystals
We report measurements of microwave (RF) generation in the centimeter band
accomplished by irradiating a nonlinear KTiOPO (KTP) crystal with a
home-made, infrared laser at nm as a result of optical rectification
(OR). The laser delivers pulse trains of duration up to s. Each train
consists of several high-intensity pulses at an adjustable repetition rate of
approximately GHz. The duration of the generated RF pulses is
determined by that of the pulse trains. We have investigated both microwave-
and second harmonic (SHG) generation as a function of the laser intensity and
of the orientation of the laser polarization with respect to the
crystallographic axes of KTP.Comment: 5 pages, 5 figures, to appear in Optics Letters, vol. 38 (2013
Microwave emission by nonlinear crystals irradiated with a high-intensity, mode-locked laser
We report on the experimental investigation of the efficiency of some
nonlinear crystals to generate microwave (RF) radiation as a result of optical
rectification (OR) when irradiated with intense pulse trains delivered by a
mode-locked laser at nm. We have investigated lithium triborate (LBO),
lithium niobate (LiNbO), zinc selenide (ZnSe), and also potassium titanyl
orthophosphate (KTP) for comparison with previous measurements. The results are
in good agreement with the theoretical predictions based on the form of the
second-order nonlinear susceptibility tensor. For some crystals we investigated
also the second harmonic generation (SHG) to cross check the theoretical model.
We confirm the theoretical prediction that OR leads to the production of higher
order RF harmonics that are overtones of the laser repetition rate.Comment: accepted for publication in Journal of Optics, in pres
Signatures of fractional Hall quasiparticles in moments of current through an antidot
The statistics of tunneling current in a fractional quantum Hall sample with
an antidot is studied in the chiral Luttinger liquid picture of edge states. A
comparison between Fano factor and skewness is proposed in order to clearly
distinguish the charge of the carriers in both the thermal and the shot limit.
In addition, we address effects on current moments of non-universal exponents
in single-quasiparticle propagators. Positive correlations, result of
propagators behaviour, are obtained in the shot noise limit of the Fano factor,
and possible experimental consequences are outlined
Finite frequency noise for edge states at filling factor
We investigate the properties of the finite frequency noise in a quantum
point contact geometry for the fractional quantum Hall state at filling factor
. The results are obtained in the framework of the Wen's hierarchical
model.
We show that the peak structure of the colored noise allows to discriminate
among different possible excitations involved in the tunneling. In particular,
optimal values of voltage and temperature are found in order to enhance the
visibility of the peak associated with the tunneling of a 2-agglomerate, namely
an excitation with charge double of the fundamental one associated to the
single quasiparticle.Comment: 5 pages, 1 figure, to be published in the Proceedings of the
Conference on the Frontiers of Quantum and Mesoscopic Thermodynamics (FQMT11
Multiple quasiparticle Hall spectroscopy investigated with a resonant detector
We investigate the finite frequency (f.f.) noise properties of edge states in
the quantum Hall regime. We consider the measurement scheme of a resonant
detector coupled to a quantum point contact in the weak-backscattering limit. A
detailed analysis of the difference between the "measured" noise, due to the
presence of the resonant detector, and the symmetrized f.f. noise is presented.
We discuss both the Laughlin and Jain sequences, studying the tunnelling
excitations in these hierarchical models. We argue that the measured noise can
better distinguish between the different excitations in the tunnelling process
with respect to the symmetrized f.f. counterpart in an experimentally relevant
range of parameters. Finally, we illustrate the effect of the detector
temperature on the sensibility of this measure.Comment: 24 pages, 8 figure
Photonic heat conduction in Josephson-coupled Bardeen-Cooper-Schrieffer superconductors
We investigate the photon-mediated heat flow between two Josephson-coupled
Bardeen-Cooper-Schrieffer (BCS) superconductors. We demonstrate that in
standard low temperature experiments involving temperature-biased
superconducting quantum interference devices (SQUIDs), this radiative
contribution is negligible if compared to the direct galvanic one, but it
largely exceeds the heat exchanged between electrons and the lattice phonons.
The corresponding thermal conductance is found to be several orders of
magnitude smaller, for real experiments setup parameters, than the universal
quantum of thermal conductance, kappa_0(T)=pi k_B^2T/6hbar.Comment: 8 pages, 6 figure
Photoconductance of a one-dimensional quantum dot
The ac-transport properties of a one-dimensional quantum dot with non-Fermi
liquid correlations are investigated. It is found that the linear
photoconductance is drastically influenced by the interaction. Temperature and
voltage dependences of the sideband peaks are treated in detail. Characteristic
Luttinger liquid power laws are founded.Comment: accepted in European Physical Journal
Ferromagnetic insulator-based superconducting junctions as sensitive electron thermometers
We present an exhaustive theoretical analysis of charge and thermoelectric
transport in a normal metal-ferromagnetic insulator-superconductor (NFIS)
junction, and explore the possibility of its use as a sensitive thermometer. We
investigated the transfer functions and the intrinsic noise performance for
different measurement configurations. A common feature of all configurations is
that the best temperature noise performance is obtained in the non-linear
temperature regime for a structure based on an europium chalcogenide
ferromagnetic insulator in contact with a superconducting Al film structure.
For an open-circuit configuration, although the maximal intrinsic temperature
sensitivity can achieve nKHz, a realistic amplifying chain will
reduce the sensitivity up to KHz. To overcome this limitation
we propose a measurement scheme in a closed-circuit configuration based on
state-of-art SQUID detection technology in an inductive setup. In such a case
we show that temperature noise can be as low as nKHz. We also
discuss a temperature-to-frequency converter where the obtained thermo-voltage
developed over a Josephson junction operated in the dissipative regime is
converted into a high-frequency signal. We predict that the structure can
generate frequencies up to GHz, and transfer functions up to
GHz/K at around K. If operated as electron thermometer, the device
may provide temperature noise lower than nKHz thereby being
potentially attractive for radiation sensing applications.Comment: 11 pages, 10 color figure
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