12 research outputs found
Controlling intense, ultrashort, laser-driven relativistic mega-ampere electron fluxes by a modest, static magnetic field
The guiding and control of ultrahigh flux, femtosecond relativistic electron
pulses through solid density matter is of great importance for many areas of
high energy density science. Efforts so far include the use of magnetic fields
generated by the propagation of the electron pulse itself or the application of
hundreds of Tesla magnitudes, pulsed external magnetic fields driven by either
short pulse lasers or electrical pulses. Here we experimentally demonstrate the
guiding of hundreds of keV mega-ampere electron pulses in a magnetized
neodymium solid that has a very modest, easily available static field of 0.1
tesla. The electron pulses driven by an ultrahigh intensity, 30 femtosecond
laser are shown to propagate beam-like, a distance as large as 5 mm in a high Z
target (neodymium), their collimation improved and flux density enhanced nearly
by a factor of 3. Particle-in-cell simulations in the appropriate parameter
regime match the experimental observations. In addition, the simulations
predict the occurrence of a novel, near-monochromatic feature towards the high
energy end of the electron energy spectrum, which is tunable by the applied
magnetic field strength. These results may prove valuable for fast electron
beam-driven radiation sources, fast ignition of laser fusion, and laboratory
astrophysics.Comment: 10 pages, 5 figure
Collimated hot electron generation from sub-wavelength grating target irradiated by a femtosecond laser pulse of relativistic intensity
We investigate the production of hot electrons from the interaction of
relativistically intense () ultra-short (25 fs) laser
pulses with sub-wavelength grating target. We measure the hot electron angular
distribution and energy spectra for grating target and compare them with those
from a planar mirror target. We observe that hot electrons are emitted in a
collimated beam along the specular direction of the grating target. From the
measured electron energy spectra we see electron temperature for grating is
higher than the mirror, suggesting a higher electron yield and hence a stronger
coupling with the laser. We performed numerical simulations which are in good
agreement with experimental results, offer insights into the acceleration
mechanism by resulting electric and magnetic fields. Such collimated fast
electron beams have a wide range of applications in applied and fundamental
science.Comment: 6 figure
Generation of a strong reverse shock wave in the interaction of a high-contrast high-intensity femtosecond laser pulse with a silicon target
We present ultrafast pump-probe reflectivity and Doppler spectrometry of a silicon target at relativistic laser intensity. We observe an unexpected rise in reflectivity to a peak approximately9 ps after the main pulse interaction with the target. This occurs after the reflectivity has fallen off from the initially high “plasma-mirror” phase. Simultaneously measured time-dependent Doppler shift data show an increase in the blue shift at the same time. Numerical simulations show that the aforementioned trends in the experimental measurements correspond to a strong shock wave propagating back toward the laser. The relativistic laser-plasma interaction indirectly heats the cool-dense (ne 10^23 cm^-3 and Te ~10eV) target material adjacent to the corona, by hot electron induced return current heating, raising its temperature to around 150eV and causing it to explode violently. The increase in reflectivity is caused by the transient steepening of the plasma density gradient at the probe critical surface due to this explosive behavior
Recombination of Protons Accelerated by a High Intensity High Contrast Laser
Short pulse, high contrast, intense laser pulses incident onto a solid target are not known to generate fast neutral atoms. Experiments carried out to study the recombination of accelerated protons show a 200 times higher neutralization than expected. Fast neutral atoms can contribute to 80% of the fast particles at 10 keV, falling rapidly for higher energy. Conventional charge transfer and electron-ion recombination in a high density plasma plume near the target is unable to explain the neutralization. We present a model based on the copropagation of electrons and ions wherein recombination far away from the target surface accounts for the experimental measurements. A novel experimental verification of the model is also presented. This study provides insights into the closely linked dynamics of ions and electrons by which neutral atom formation is enhanced
Femtosecond, two-dimensional spatial Doppler mapping of ultraintense laser-solid target interaction
We present measurements of the spatio-temporal evolution of a hot-dense plasma generated by the interaction of an intense 25 femtosecond laser pulse with a solid target, using pump-probe two-dimensional Doppler spectrometry. Measuring the time-dependent Doppler shifts at different positions across the probe beam, we achieve velocity mapping at hundreds of femtoseconds time resolution simultaneously with a few micrometer spatial resolution across the transverse length of the plasma. Simulations of the interaction using a combination of 2D particle-in-cell (PIC) and 2D radiation hydrodynamics codes agree well with the experiment
Tracking ultrafast dynamics of intense shock generation and breakout at target rear
We report upon the picosecond plasma dynamics at the rear surface of a thin aluminium foil (of either 5.5 um or 12 um thickness) excited by high contrast (picosecond intensity contrast of 10^10), 800 nm, femtosecond pulses at an intensity of 3 x 10^19 W/cm2. We employ ultrafast pump-probe reflectometry using a second harmonic probe (400 nm) interacting with the rear surface of the target. A rise in the probe reflectivity 30 picoseconds after the pump pulse interaction reveals the breakout of a shock wave at the target rear surface which reflects the 400 nm probe pulse. Simulations using the ZEPHYROS hybrid particle-in-cell code were performed to understand the heating of the target under the influence of the high intensity laser pulse, and the temperature profile was then passed to the radiation-hydrodynamics simulation code HYADES in order to model the shock wave propagation in the target. A good agreement was found between the calculations and experimental results
Biochemical studies on ethyl methane sulfonate induced chlorena mutant of Triticum dicoccum var. Khapli
This article does not have an abstract
Efficient second-harmonic generation of a high-energy, femtosecond laser pulse in a lithium triborate crystal
International audienc
Single-Shot, Spatio-Temporal Metrology of Relativistic Plasma Optics
Plasma optics, promising for shaping and amplifying ultrahigh-power laser pulses, are subject to huge modulations and fluctuations inherent in the excitation at high intensities. Understanding their impact on the spatio-temporal structure of resulting pulses demands multidimensional characterization of relativistic plasma dynamics, an extremely difficult task, particularly at the low repetition rates typical of such lasers. Here, we present three-dimensional (3D) spatio-temporal measurements of such pulses based on spectral interferometry. We measure the complex space-time distortions induced in the laser pulses by relativistic plasma while simultaneously capturing the underlying plasma dynamics, all in a single shot. This all-optical technique can capture 3D spatio-temporal couplings within pulses at ultrahigh peak powers, enabling further progress in ultrahigh-intensity laser and plasma technologies