Detector for imaging and dosimetry of laser-driven epithermal neutrons by alpha conversion

An epithermal neutron imager based on detecting alpha particles created by boron neutron capture mechanism is discussed. The diagnostic mainly consists of a mm thick Boron Nitride (BN) sheet (as an alpha converter) in contact with a non-borated cellulose nitride film (LR115 type-II) detector. While the BN absorbs the neutrons below 0.1 eV, the fast neutrons register insignificantly in the detector due to their low neutron capture and recoil cross-sections. The use of solid-state nuclear track detectors (SSNTD), unlike image plates, micro-channel plates and scintillators, provide safeguard from the x-rays, gamma-rays and electrons. The diagnostic was tested on a proof-of-principle basis, in front of a laser driven source of moderated neutrons, which suggests the potential of using this diagnostic (BN+SSNTD) for dosimetry and imaging applications

Characterization of laser plasmas for interaction studies: Progress in time-resolved density mapping

Time-resolved probe interferometry was used to obtain complete density mapping of laser produced plasmas. The plasma was produced by symmetrical irradiation of thin targets, to be used for short pulse delayed interaction experiments. The progress in the plasma characterization due to the use of a picosecond pulse probe is reported, and the relative merits of different target designs are also discussed. The two-dimensional density maps obtained appear to be in substantial agreement with two-dimensional hydrodynamic code predictions

High-energy electron beam production by femtosecond laser interactions with exploding-foil plasmas

International audienceThe interaction of an ultraintense, 30-fs laser pulse with a preformed plasma was investigated as a method of producing a beam of high-energy electrons. We used thin foil targets that are exploded by the laser amplified spontaneous emission preceding the main pulse. Optical diagnostics show that the main pulse interacts with a plasma whose density is well below the critical density. By varying the foil thickness, we were able to obtain a substantial emission of electrons in a narrow cone along the laser direction with a typical energy well above the laser ponderomotive potential. These results are explained in terms of wake-field acceleration

Propagation issues and fast particle source characterization in laser-plasma interactions at intensities exceeding 10(19) W/cm(2)

A series of experiments recently carried out at the Rutherford Appleton Laboratory investigated various aspects of the laser-plasma interaction in the relativistic intensity regime. The propagation of laser pulses through preformed plasmas was studied at intensities exceeding 10(19) W/cm(2). The transmission of laser energy through long scale underdense plasmas showed to be inefficient unless a plasma channel is preformed ahead of the main laser pulse. The study of the interaction with overdense plasmas yielded indication of propagation at densities above the critical density, possible due to relativistic effects. The production of fast particles during the interaction with solid density targets was also investigated. The measurements revealed the presence of a small-sized directional source of multi-MeV protons, which was not observed when a plasma was preformed at the back of the solid target. The properties of the source are promising in view of its use in radiographic imaging of dense matter, and preliminary tests were carried out