52 research outputs found
Optimisation of Thin Plastic Foil Targets for Production of Laser-Generated Protons in the GeV Range
In order to realistically simulate the interaction of a femtosecond laser
pulse with a nanometre-thick target it is necessary to consider a target
preplasma formation due to the nanosecond long amplified-spontaneous-emission
pedestal and/or prepulse. The relatively long interaction time dictated that
hydrodynamic simulations should be employed to predict the target particles'
number density distributions prior the arrival of the main laser pulse. By
using the output of the hydrodynamic simulations as input into particle-in-cell
simulations, a detailed understanding of the complete laser-foil interaction is
achieved. Once the laser pulse interacts with the preplasma it deposits a
fraction of its energy on the target, before it is either reflected from the
critical density surface or transmitted through an underdense plasma channel. A
fraction of hot electrons is ejected from the target leaving the foil in a net
positive potential, which in turn results in proton and heavy ion ejection. In
this work protons reaching ~25 MeV are predicted for a laser of ~40 TW peak
power and ~600 MeV are expected from a ~4 PW laser system.Comment: 17 pages, 21 figure
Ultrashort PW laser pulse interaction with target and ion acceleration
We present the experimental results on ion acceleration by petawatt
femtosecond laser solid interaction and explore strategies to enhance ion
energy. The irradiation of micrometer thick (0.2 - 6.0 micron) Al foils with a
virtually unexplored intensity regime (8x10^19 W/cm^2 - 1x10^21 W/cm^2)
resulting in ion acceleration along the rear and the front surface target
normal direction is investigated. The maximum energy of protons and carbon
ions, obtained at optimised laser intensity condition (by varying laser energy
or focal spot size), exhibit a rapid intensity scaling as I^0.8 along the rear
surface target normal direction and I^0.6 along the front surface target normal
direction. It was found that proton energy scales much faster with laser energy
rather than the laser focal spot size. Additionally, the ratio of maximum ion
energy along the both directions is found to be constant for the broad range of
target thickness and laser intensities. A proton flux is strongly dominated in
the forward direction at relatively low laser intensities. Increasing the laser
intensity results in the gradual increase in the backward proton flux and leads
to almost equalisation of ion flux in both directions in the entire energy
range. These experimental findings may open new perspectives for applications.Comment: 6 pages, 5 figures, 3rd EAAC worksho
Gamma-Flash Generation in Multi-Petawatt Laser-Matter Interactions
The progressive development of high power lasers over the last several
decades, enables the study of -photon generation when an intense laser
beam interacts with matter, mainly via inverse Compton scattering at the high
intensity limit. -ray flashes are a phenomenon of broad interest,
drawing attention of researchers working in topics ranging from cosmological
scales to elementary particle scales. Over the last few years, a plethora of
studies predict extremely high laser energy to -photon energy
conversion using various target and/or laser field configurations. The aim of
the present manuscript is to discuss several recently proposed -ray
flash generation schemes, as a guide for upcoming -photon related
experiments and for further evolution of the presently available theoretical
schemes.Comment: 12 pages, 8 figure
Ultrashort PW laser pulse interaction with target and ion acceleration
We present the experimental results on ion acceleration by petawatt femtosecond laser solid interaction and explore strategies to enhance ion energy. The irradiation of micrometer thick (0.2-6.0 mu m) Al foils with a virtually unexplored intensity regime (8 x 10(19) W/cm(2) - 1 x 10(21) W/cm(2)) resulting in ion acceleration along the rear and the front surface target normal direction is investigated. The maximum energy of protons and carbon ions, obtained at optimized laser intensity condition (by varying laser energy or focal spot size), exhibit a rapid intensity scaling as I-0.8 along the rear surface target normal direction and I-0.6 along the front surface target normal direction. It was found that proton energy scales much faster with laser energy rather than the laser focal spot size. Additionally, the ratio of maximum ion energy along the both directions is found to be constant for the broad range of target thickness and laser intensities. A proton flux is strongly dominated in the forward direction at relatively low laser intensities. Increasing the laser intensity results in the gradual increase in the backward proton flux and leads to almost equalization of ion flux in both directions in the entire energy range. These experimental findings may open new perspectives for applications
Quantifying the Speed of Chromatophore Activity at the Single-Organ Level in Response to a Visual Startle Stimulus in Living, Intact Squid
The speed of adaptive body patterning in coleoid cephalopods is unmatched in the natural world. While the literature frequently reports their remarkable ability to change coloration significantly faster than other species, there is limited research on the temporal dynamics of rapid chromatophore coordination underlying body patterning in living, intact animals. In this exploratory pilot study, we aimed to measure chromatophore activity in response to a light flash stimulus in seven squid, Doryteuthis pealeii. We video-recorded the head/arms, mantle, and fin when squid were presented with a light flash startle stimulus. Individual chromatophores were detected and tracked over time using image analysis. We assessed baseline and response chromatophore surface area parameters before and after flash stimulation, respectively. Using change-point analysis, we identified 4,065 chromatophores from 185 trials with significant surface area changes elicited by the flash stimulus. We defined the temporal dynamics of chromatophore activity to flash stimulation as the latency, duration, and magnitude of surface area changes (expansion or retraction) following the flash presentation. Post stimulation, the response’s mean latency was at 50 ms (± 16.67 ms), for expansion and retraction, across all body regions. The response duration ranged from 217 ms (fin, retraction) to 384 ms (heads/arms, expansion). While chromatophore expansions had a mean surface area increase of 155.06%, the retractions only caused a mean reduction of 40.46%. Collectively, the methods and results described contribute to our understanding of how cephalopods can employ thousands of chromatophore organs in milliseconds to achieve rapid, dynamic body patterning
Surface modulation and back reflection from foil targets irradiated by a Petawatt femtosecond laser pulse at oblique incidence
A significant level of back reflected laser energy was measured during the interaction of ultra-short, high contrast PW laser pulses with solid targets at 30 degrees incidence. 2D PIC simulations carried out for the experimental conditions show that at the laser-target interface a dynamic regular structure is generated during the interaction, which acts as a grating (quasi-grating) and reflects back a significant amount of incident laser energy. With increasing laser intensity above 1018 W/cm(2) the back reflected fraction increases due to the growth of the surface modulation to larger amplitudes. Above 1020 W/cm(2) this increase results in the partial destruction of the quasi-grating structure and, hence, in the saturation of the back reflection efficiency. The PIC simulation results are in good agreement with the experimental findings, and, additionally, demonstrate that in presence of a small amount of pre-plasma this regular structure will be smeared out and the back reflection reduced. (C) 2016 Optical Society of Americ
- …