EVALUATION OF A FOAM BUFFER TARGET DESIGN FOR SPATIALLY UNIFORM ABLATION OF LASER-IRRADIATED PLASMAS

Experimental observations are presented demonstrating that the use of a gold-coated foam layer on the surface of a laser-driven target substantially reduces its hydrodynamic breakup during the acceleration phase. The data suggest that this results from enhanced thermal smoothing during the early-time imprint stage of the interaction. The target's kinetic energy and the level of parametric instability growth are shown to remain essentially unchanged from that of a conventionally driven target.

Langmuir probe measurements of plasma parameters in the late stages of a laser ablated plume

A simple Langmuir probe technique has been used to measure the electron density, electron temperature, and plasma potential in the late stages (>5 mu s) of a laser ablated plasma plume. In the plasma, formed following 248 nm laser irradiation of a copper target, in vacuum at a laser fluence of 2.5 J cm(-2), electron densities of similar to 10(18) m(-3) and temperatures of similar to 0.5 eV were measured. These values are comparable with those reported previously using Faraday cup detectors and optical emission spectroscopy, respectively. (C) 1997 American Institute of Physics.

OPTICAL-ABSORPTION SPECTROSCOPY STUDY OF THE ROLE OF PLASMA CHEMISTRY IN YBA2CU3O7 PULSED LASER DEPOSITION

Time-resolved optical absorption spectroscopy techniques were used to study Ba, metastable Ba+, and YO absorptions in the laser-produced plasma plume from a YBa2Cu3O7 target. Results obtained indicate an initial explosive removal of material from the target sur-face followed by a subsequent evaporation process. Some YO is ejected from the target in molecular form, particularly at laser fluence

Ethanol (C2H5OH) spray of sub-micron droplets for laser driven negative ion source

Liquid ethanol (C₂H₅OH) was used to generate a spray of sub-micron droplets. Sprays with different nozzle geometries have been tested and characterised using Mie scattering to find scaling properties and to generate droplets with different diameters within the spray. Nozzles having throat diameters of 470 µm and 560 µm showed generation of ethanol spray with droplet diameters of (180 ± 10) nm and (140 ± 10) nm, respectively. These investigations were motivated by the observation of copious negative ions from these target systems, e.g., negative oxygen and carbon ions measured from water and ethanol sprays irradiated with ultra-intense (5 × 1019 W/cm2), ultra short (40 fs) laser pulses. It is shown that the droplet diameter and the average atomic density of the spray have a significant effect on the numbers and energies of accelerated ions, both positive and negative. These targets open new possibilities for the creation of efficient and compact sources of different negative ion species.

Simulation of relativistically colliding laser-generated electron flows

The plasma dynamics resulting from the simultaneous impact, of two equal, ultra-intense laser pulses, in two spatially separated spots, onto a dense target is studied via particle-in-cell simulations. The simulations show that electrons accelerated to relativistic speeds cross the target and exit at its rear surface. Most energetic electrons are bound to the rear surface by the ambipolar electric field and expand along it. Their current is closed by a return current in the target, and this current configuration generates strong surface magnetic fields. The two electron sheaths collide at the midplane between the laser impact points. The magnetic repulsion between the counter-streaming electron beams separates them along the surface normal direction, before they can thermalize through other beam instabilities. This magnetic repulsion is also the driving mechanism for the beam-Weibel (filamentation) instability, which is thought to be responsible for magnetic field growth close to the internal shocks of gamma-ray burst jets. The relative strength of this repulsion compared to the competing electrostatic interactions, which is evidenced by the simulations, suggests that the filamentation instability can be examined in an experimental setting. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4768426]