836 research outputs found
Investigation of a 2-Colour Undulator FEL Using Puffin
Initial studies of a 2-colour FEL amplifier using one monoenergetic electron
beam are presented. The interaction is modelled using the unaveraged, broadband
FEL code Puffin. A series of undulator modules are tuned to generate two
resonant frequencies along the FEL interaction and a self-consistent 2-colour
FEL interaction at widely spaced non-harmonic wavelengths at 1nm and 2.4nm is
demonstrated.Comment: Submitted to The 35th International Free-Electron Laser Conference,
Manhattan, New York (2013
Development of Prototype Pixellated PIN CdZnTe Detectors
We report initial results from the design and evaluation of two pixellated
PIN Cadmium Zinc Telluride detectors and an ASIC-based readout system. The
prototype imaging PIN detectors consist of 4X4 1.5 mm square indium anode
contacts with 0.2 mm spacing and a solid cathode plane on 10X10 mm CdZnTe
substrates of thickness 2 mm and 5 mm. The detector readout system, based on
low noise preamplifier ASICs, allows for parallel readout of all channels upon
cathode trigger. This prototype is under development for use in future
astrophysical hard X-ray imagers with 10-600 keV energy response. Measurements
of the detector uniformity, spatial resolution, and spectral resolution will be
discussed and compared with a similar pixellated MSM detector. Finally, a
prototype design for a large imaging array is outlined.Comment: 10 pages Latex, 9 figures, to appear in Proc. of SPIE Vol. 3446 "Hard
X-ray and Gamma-Ray Detector Physics and Applications
Magnetization reversal and local switching fields of ferromagnetic Co/Pd microtubes with radial magnetization
Three-dimensional nanomagnetism is a rapidly growing field of research covering both noncollinear spin textures and curved magnetic geometries including microtubular structures. We spatially resolve the field-induced magnetization reversal of free-standing ferromagnetic microtubes utilizing multifrequency magnetic force microscopy (MFM). The microtubes are composed of Co/Pd multilayer films with perpendicular magnetic anisotropy that translates to an anisotropy with radial easy axis upon rolling-up. Simultaneously mapping the topography and the perpendicular magnetostatic force derivative, the relation between surface angle and local magnetization configuration is evaluated for a large number of locations with slopes exceeding 45 degrees. The angle-dependence of the switching field is concurrent with the Kondorsky model, i.e., the rolled-up nanomembrane behaves like a planar magnetic film with perpendicular anisotropy and a pinning dominated magnetization reversal. Additionally, we discuss methodological challenges when detecting magnetostatic force derivatives near steep surfaces
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Single-electron transitions in one-dimensional native nanostructures
Low-temperature measurements proved the existence of a two-dimensional electron gas at defined dislocation arrays in silicon. As a consequence, single-electron transitions (Coulomb blockades) are observed. It is shown that the high strain at dislocation cores modifies the band structure and results in the formation of quantum wells along dislocation lines. This causes quantization of energy levels inducing the formation of Coulomb blockades
Design considerations for table-top, laser-based VUV and X-ray free electron lasers
A recent breakthrough in laser-plasma accelerators, based upon ultrashort
high-intensity lasers, demonstrated the generation of quasi-monoenergetic
GeV-electrons. With future Petawatt lasers ultra-high beam currents of ~100 kA
in ~10 fs can be expected, allowing for drastic reduction in the undulator
length of free-electron-lasers (FELs). We present a discussion of the key
aspects of a table-top FEL design, including energy loss and chirps induced by
space-charge and wakefields. These effects become important for an optimized
table-top FEL operation. A first proof-of-principle VUV case is considered as
well as a table-top X-ray-FEL which may open a brilliant light source also for
new ways in clinical diagnostics.Comment: 6 pages, 4 figures; accepted for publication in Appl. Phys.
Experimental characterization of superradiance in a single-pass high-gain laser-seeded free-electron laser amplifier.
In this Letter we report the first experimental characterization of superradiance in a single-pass high-gain free-electron laser (FEL) seeded by a 150 femtosecond (FWHM) Ti:sapphire laser. The nonlinear energy gain after an exponential gain regime was observed. We also measured the evolution of the longitudinal phase space in both the exponential and superradiant regimes. The output FEL pulse duration was measured to be as short as 81 fs, a roughly 50% reduction compared to the input seed laser. The temporal distribution of the FEL radiation as predicted by a numerical simulation was experimentally verified for the first time
INVESTIGATION OF A 2-COLOUR UNDULATOR FEL USING PUFFIN
Abstract Initial studies of a 2-colour FEL amplifier using one monoenergetic electron beam are presented. The interaction is modelled using the unaveraged, broadband FEL code Puffin. A series of undulator modules are tuned to generate two resonant frequencies along the FEL interaction and a self-consistent 2-colour FEL interaction at widely spaced non-harmonic wavelengths at 1nm and 2.4nm is demonstrated
Employing electro-mechanical analogies for co-resonantly coupled cantilever sensors
Understanding the behaviour of mechanical systems can be facilitated and
improved by employing electro-mechanical analogies. These analogies enable
the use of network analysis tools as well as purely analytical treatment of
the mechanical system translated into an electric circuit. Recently, we
developed a novel kind of sensor set-up based on two coupled cantilever beams
with matched resonance frequencies (co-resonant coupling) and possible
applications in magnetic force microscopy and cantilever
magnetometry. In order to analyse the sensor's behaviour in detail,
we describe it as an electric circuit model. Starting from a simplified
coupled harmonic oscillator model with neglected damping, we gradually
increase the complexity of the system by adding damping and interaction
elements. For each stage, various features of the coupled system are
discussed and compared to measured data obtained with a co-resonant sensor.
Furthermore, we show that the circuit model can be used to derive sensor
parameters which are essential for the evaluation of measured data. Finally,
the much more complex circuit representation of a bending beam is discussed,
revealing that the simplified circuit model of a coupled harmonic oscillator
is a very good representation of the sensor system
Si-compatible candidates for high-K dielectrics with the Pbnm perovskite structure
We analyze both experimentally (where possible) and theoretically from
first-principles the dielectric tensor components and crystal structure of five
classes of Pbnm perovskites. All of these materials are believed to be stable
on silicon and are therefore promising candidates for high-K dielectrics. We
also analyze the structure of these materials with various simple models,
decompose the lattice contribution to the dielectric tensor into force constant
matrix eigenmode contributions, explore a peculiar correlation between
structural and dielectric anisotropies in these compounds and give phonon
frequencies and infrared activities of those modes that are infrared-active. We
find that CaZrO_3, SrZrO_3, LaHoO_3, and LaYO_3 are among the most promising
candidates for high-K dielectrics among the compounds we considered.Comment: 17 pages, 9 figures, 4 tables. Supplementary information:
http://link.aps.org/supplemental/10.1103/PhysRevB.82.064101 or
http://www.physics.rutgers.edu/~sinisa/highk/supp.pd
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