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Energy spectra of fast electrons, generated when high-intensity laser pulses irradiated hollow conical targets, have been measured experimentally. It is shown here that the slope temperature of the fast electrons is strongly dependent on the opening angle of the cone, and has a maximum value at 25°. The data confirms optical guiding of the laser pulse, by comparison of the measured electron temperature with ray-tracing calculations that include absorption in plasmas. The enhanced energy flow and intensity induced by optical guiding of the laser pulse inside the cone as a function of the opening angle as well as the f-number of the focusing optics is discussed. [ABSTRACT FROM AUTHOR]

We have developed an advanced design for a time-of-flight (TOF) neutron spectrometer applied to the study of ultraintense laser-plasma interactions in the area of fast ignition research. The interaction of an ultraintense laser pulse with plasma creates intense gamma rays, which generate a high level of background noise in the thermal neutron detection process. High energy-density ions, which are generated by strong electric fields associated with the laser interactions, produce beamlike fusion neutrons with an angular distribution that is dependent on the momentum distribution of the ions. These beamlike fusion neutrons also act as a source of significant background noise in the thermal neutron detection process. In order to improve the signal-to-noise ratio (S/N), we have proposed and applied a wave-coincidence method to the neutron detection process. We have demonstrated the advantages of this advanced method in ultraintense laser-plasma interaction experiments, where an improvement in S/N by a factor of 7–8 compared to the conventional TOF method was achieved. We have calculated that the value of S/N increases with the number of detectors used as well as with the initial value of S/N for a single detector. [ABSTRACT FROM AUTHOR]

Energetic electrons were generated by the interaction of a high-intensity laser pulse with a plasma preformed from a hollow plastic cylinder via laser-driven implosion. The spectra of a comparatively high-density plasma ∼1019 cm-3 had a bump around 10 MeV. Simple numerical calculations explained the spectra obtained in this experiment. This indicates that the plasma tube has sufficient potential to convert a Maxwellian spectrum to a comparatively narrow spectrum. [ABSTRACT FROM AUTHOR]