835 research outputs found
Application of novel techniques for interferogram analysis to laser-plasma femtosecond probing
Recently, two novel techniques for the extraction of the phase-shift map
(Tomassini {\it et.~al.}, Applied Optics {\bf 40} 35 (2001)) and the electronic
density map estimation (Tomassini P. and Giulietti A., Optics Communication
{\bf 199}, pp 143-148 (2001)) have been proposed. In this paper we apply both
methods to a sample laser-plasma interferogram obtained with femtoseconds probe
pulse, in an experimental setup devoted to laser particle acceleration studies.Comment: Submitted to Laser and Particle Beam
A Generalization of Abel Inversion to non axisymmetric density distribution
Abel Inversion is currently used in laser-plasma studies in order to estimate
the electronic density from the phase-shift map obtained
via interferometry. The main limitation of the Abel method is due to the
assumption of axial symmetry of the electronic density, which is often hardly
fulfilled. In this paper we present an improvement to the Abel inversion
technique in which the axial symmetry condition is relaxed by means of a
truncated Legendre Polinomial expansion in the azimutal angle. With the help of
simulated interferograms, we will show that the generalized Abel inversion
generates accurate densities maps when applied to non axisymmetric density
sources
Quantitative global-local mixing for accessible skew products
We study global-local mixing for accessible skew products with a mixing base.
For a dense set of almost periodic global observables, we prove rapid mixing;
and for a dense set of global observables vanishing at infinity, we prove
polynomial mixing. More generally, we relate the speed of mixing to the "low
frequency behaviour" of the spectral measure associated to our global
observables. Our strategy relies on a careful choice of the spaces of
observables and on the study of a family of twisted transfer operators
Experimental study of picosecond laser plasma formation in thin foils
A high performance, fully controlled picosecond
laser system has been designed and built with the aid of
a numerical code capable of simulating the temporal behavior
of the laser system, including each active and passive
component. The laser performance was characterized with
an optical streak camera, equivalent plane monitor, and
calorimeter measurements. The laser pulse was focused on
150-nm thick foils to investigate plasma formation and
the related transmittivity of the laser light. The experimental
data are in very good agreement with the predictions of
a simple, 2D analytical model that takes into account the
actual shot-to-shot features of the laser pulse. The temporal
profile of the pulse and the intensity distribution in
the focal spot were found to play a key role in determining
the transmission properties of the laser-irradiated foil.
This work may be relevant to a wide class of laser exploded
foil plasma experiments
Expanding Semiflows on Branched Surfaces and One-Parameter Semigroups of Operators
We consider expanding semiflows on branched surfaces. The family of transfer
operators associated to the semiflow is a one-parameter semigroup of operators.
The transfer operators may also be viewed as an operator-valued function of
time and so, in the appropriate norm, we may consider the vector-valued Laplace
transform of this function. We obtain a spectral result on these operators and
relate this to the spectrum of the generator of this semigroup. Issues of
strong continuity of the semigroup are avoided. The main result is the
improvement to the machinery associated with studying semiflows as
one-parameter semigroups of operators and the study of the smoothness
properties of semiflows defined on branched manifolds, without encoding as a
suspension semiflow
Ray-tracing simulations of a bent crystal X-ray optics for imaging using laser-plasma X-ray sources
Ray-tracing simulations of an optical X-ray system based on a spherically bent crystal operating in Bragg configuration for monochromatic projection imaging of thin samples are presented, obtained using a code developed for that purpose. The code is particularly suited for characterizing experimental arrangements routinely used with laser-produced plasma X-ray sources. In particular, the spatial resolution of the imaging system was investigated and a careful study of the complex pattern of the X-ray backlighting beam was performed
Acceleration with Self-Injection for an All-Optical Radiation Source at LNF
We discuss a new compact gamma-ray source aiming at high spectral density, up
to two orders of magnitude higher than currently available bremsstrahlung
sources, and conceptually similar to Compton Sources based on conventional
linear accelerators. This new source exploits electron bunches from
laser-driven electron acceleration in the so-called self-injection scheme and
uses a counter-propagating laser pulse to obtain X and gamma-ray emission via
Thomson/Compton scattering. The proposed experimental configuration inherently
provides a unique test-bed for studies of fundamental open issues of
electrodynamics. In view of this, a preliminary discussion of recent results on
self-injection with the FLAME laser is also given.Comment: 8 pages, 10 figures, 44 references - Channeling 2012 conferenc
Space- and time-resolved observation of extreme laser frequency upshifting during ultrafast-ionization
A 65-fs, 800-nm, 2-TW laser pulse propagating through a nitrogen gas jet has been experimentally studied by 90 Thomson scattering. Time-integrated spectra of scattered light show unprecedented broadening towards the blue which exceeds 300 nm. Images of the scattering region provide for the first time a space- and time-resolved description of the process leading quite regularly to such a large upshift. The mean shifting rate was as high as dk/dt3A ĚŠ/fs, never observed before. Interferometry shows that it occurs after partial laser defocusing. Numerical simulations prove that such an upshift is consistent with a laser-gas late interaction, when laser intensity has decreased well below relativistic values (a0 1) and ionization process involves most of the laser pulse. This kind of interaction makes spectral tuning of ultrashort intense laser pulses possible in a large spectral range. VC 2013 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4818602
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