60,179 research outputs found
Advanced infrared laser modulator development
A parametric study was conducted to develop an electrooptic waveguide modulator for generating continuous tunable sideband power from an infrared CO2 laser. Parameters included were the waveguide configurations, microstrip dimensions device impedance, and effective dielectric constants. An optimum infrared laser modulator was established and was fabricated. This modulator represents the state-of-the-art integrated optical device, which has a three-dimensional topology to accommodate three lambda/4 step transformers for microwave impedance matching at both the input and output terminals. A flat frequency response of the device over 20 HGz or = 3 dB) was achieved. Maximum single sideband to carrier power greater than 1.2% for 20 W microwave input power at optical carrier wavelength of 10.6 microns was obtained
Information on the structure of the a1 from tau decay
The decay is analysed using different methods to
account for the resonance structure, which is usually ascribed to the a1. One
scenario is based on the recently developed techniques to generate axial-vector
resonances dynamically, whereas in a second calculation the a1 is introduced as
an explicit resonance. We investigate the influence of different assumptions on
the result. In the molecule scenario the spectral function is described
surprisingly well by adjusting only one free parameter. This result can be
systematically improved by adding higher order corrections to the iterated
Weinberg-Tomozawa interaction. Treating the a1 as an explicit resonance on the
other hand leads to peculiar properties
Cosmic-ray induced background intercomparison with actively shielded HPGe detectors at underground locations
The main background above 3\,MeV for in-beam nuclear astrophysics studies
with -ray detectors is caused by cosmic-ray induced secondaries. The
two commonly used suppression methods, active and passive shielding, against
this kind of background were formerly considered only as alternatives in
nuclear astrophysics experiments. In this work the study of the effects of
active shielding against cosmic-ray induced events at a medium deep location is
performed. Background spectra were recorded with two actively shielded HPGe
detectors. The experiment was located at 148\,m below the surface of the Earth
in the Reiche Zeche mine in Freiberg, Germany. The results are compared to data
with the same detectors at the Earth's surface, and at depths of 45\,m and
1400\,m, respectively.Comment: Minor errors corrected; final versio
Dephasing in (Ga,Mn)As nanowires and rings
To understand quantum mechanical transport in ferromagnetic semiconductor the
knowledge of basic material properties like phase coherence length and
corresponding dephasing mechanism are indispensable ingredients. The lack of
observable quantum phenomena prevented experimental access to these quantities
so far. Here we report about the observations of universal conductance
fluctuations in ferromagnetic (Ga,Mn)As. The analysis of the length and
temperature dependence of the fluctuations reveals a T^{-1} dependence of the
dephasing time.Comment: 5 pages, 4 figure
S-wave quantum entanglement in a harmonic trap
We analyze the quantum entanglement between two interacting atoms trapped in
a spherical harmonic potential. At ultra-cold temperature, ground state
entanglement is generated by the dominated s-wave interaction. Based on a
regularized pseudo-potential Hamiltonian, we examine the quantum entanglement
by performing the Schmidt decomposition of low-energy eigenfunctions. We
indicate how the atoms are paired and quantify the entanglement as a function
of a modified s-wave scattering length inside the trap.Comment: 10 pages, 5 figures, to be apear in PR
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