412 research outputs found
Amplification and generation of ultra-intense twisted laser pulses via stimulated Raman scattering
Twisted Laguerre-Gaussian lasers, with orbital angular momentum and
characterised by doughnut shaped intensity profiles, provide a transformative
set of tools and research directions in a growing range of fields and
applications, from super-resolution microcopy and ultra-fast optical
communications to quantum computing and astrophysics. The impact of twisted
light is widening as recent numerical calculations provided solutions to
long-standing challenges in plasma-based acceleration by allowing for high
gradient positron acceleration. The production of ultrahigh intensity twisted
laser pulses could then also have a broad influence on relativistic
laser-matter interactions. Here we show theoretically and with ab-initio
three-dimensional particle-in-cell simulations, that stimulated Raman
backscattering can generate and amplify twisted lasers to Petawatt intensities
in plasmas. This work may open new research directions in non-linear optics and
high energy density science, compact plasma based accelerators and light
sources.Comment: 18 pages, 4 figures, 1 tabl
High Repetition-Rate Wakefield Electron Source Generated by Few-millijoule, 30 femtosecond Laser Pulses on a Density Downramp
We report on an experimental demonstration of laser wakefield electron
acceleration using a sub-TW power laser by tightly focusing 30-fs laser pulses
with only 8 mJ pulse energy on a 100 \mu m scale gas target. The experiments
are carried out at an unprecedented 0.5 kHz repetition rate, allowing "real
time" optimization of accelerator parameters. Well-collimated and stable
electron beams with a quasi-monoenergetic peak in excess of 100 keV are
measured. Particle-in-cell simulations show excellent agreement with the
experimental results and suggest an acceleration mechanism based on electron
trapping on the density downramp, due to the time varying phase velocity of the
plasma waves.Comment: 4 pages, 5 figures, submitted to Phys. Rev. Let
The effect of phase front deformation on the growth of the filamentation instability in laser–plasma interactions
Laser pulses of 0.9 kJ/1 ns/1053 nm were focused onto low-Z plastic targets in both spherical and planar geometry. The uniformity of the resulting plasma production was studied using x-ray pinhole imaging. Evidence is provided suggesting that thermal filamentation starts to occur for irradiances on the target of I lambda(2) >= 10(14) W cm(-2) mu m(2), even on deployment of phase plates to improve the focal spot spatial uniformity. The experiments are supported by both analytical modelling and two-dimensional particle-in-cell simulations. The implications for the applications of laser-plasma interactions that require high degrees of uniform irradiation are discussed
Efficiency of energy transfer, but not external work, is maximized in stunned myocardium
There is no evidence regarding the effect of stunning on maximization of
regional myocardial external work (EW) or efficiency of energy transfer
(EET) in relation to regional afterload (end-systolic stress, sigma(es)).
To that end, we studied these relationships in both the left anterior
descending coronary artery (LADCA) and left circumflex coronary artery
regions in anesthetized, open-chest pigs before and after LADCA stunning.
In normal myocardium, EET vs. sigma(es) was maximal at 75.4 (69.7-81.0)%,
whereas EW vs. sigma(es) was submaximal at 12.0 (6.61-17.3) x 10(2)
J/m(3). Increasing sigma(es) increased EW by 18 (10-27)%. Regional
myocardial stunning decreased EET (27%) and EW (36%) and caused the
myocardium to operate both at maximal EW (EW(max)) and at maximal EET
(EET(max)). EET and EW became also more sensitive to changes in sigma(es).
In the nonstunned region the situation remained unchanged. Combining the
data from before and after stunning, both EW(max) and EET(max) displayed a
positive relationship with contractility. In conclusion, the normal
regional myocardium operated at maximal EET rather than at maximal EW.
Therefore, additional EW could be recruited by increasing regional
afterload. After myocardial stunning, the myocardium operated at both
maximal EW and maximal EET, at the cost of increased afterload
sensitivity. Contractility was a major determinant of this shift
Amplification and generation of ultra-intense twisted laser pulses via stimulated Raman scattering
Twisted Laguerre–Gaussian lasers, with orbital angular momentum and characterized by doughnut-shaped intensity profiles, provide a transformative set of tools and research directions in a growing range of fields and applications, from super-resolution microcopy and ultra-fast optical communications to quantum computing and astrophysics. The impact of twisted light is widening as recent numerical calculations provided solutions to long-standing challenges in plasma-based acceleration by allowing for high-gradient positron acceleration. The production of ultra-high-intensity twisted laser pulses could then also have a broad influence on relativistic laser–matter interactions. Here we show theoretically and with ab initio three-dimensional particle-in-cell simulations that stimulated Raman backscattering can generate and amplify twisted lasers to petawatt intensities in plasmas. This work may open new research directions in nonlinear optics and high–energy-density science, compact plasma-based accelerators and light sources
Dense plasma heating by crossing relativistic electron beams
Here we investigate, using relativistic fluid theory and Vlasov-Maxwell simulations, the local heating of a dense plasma by two crossing electron beams. Heating occurs as an instability of the electron beams drives Langmuir waves, which couple nonlinearly into damped ion-acoustic waves. Simulations show a factor 2.8 increase in electron kinetic energy with a coupling efficiency of 18%. Our results support applications to the production of warm dense matter and as a driver for inertial fusion plasmas
High orbital angular momentum harmonic generation
We identify and explore a high orbital angular momentum (OAM) harmonics generation and amplification mechanism that manipulates the OAM independently of any other laser property, by preserving the initial laser wavelength, through stimulated Raman backscattering in a plasma. The high OAM harmonics spectra can extend at least up to the limiting value imposed by the paraxial approximation. We show with theory and particle-in-cell simulations that the orders of the OAM harmonics can be tuned according to a selection rule that depends on the initial OAM of the interacting waves. We illustrate the high OAM harmonics generation in a plasma using several examples including the generation of prime OAM harmonics. The process can also be realized in any nonlinear optical Kerr media supporting three-wave interactions.info:eu-repo/semantics/publishedVersio
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