Self-Injection and Acceleration of Monoenergetic Electron Beams from Laser Wakefield Accelerators in a Highly Relativistic Regime

Self-injection and acceleration of monoenergetic electron beams from laser wakefield accelerators are first investigated in the highly relativistic regime, using 100 TW class, 27 fs laser pulses. Quasi-monoenergetic multi- bunched beams with energies as high as multi-hundredMeV are observed with simultaneous measurements of side-scattering emissions that indicate the formation of self-channelfing and self-injection of electrons into a plasma wake, referred to as a ＇bubble＇. The three-dimensional particle-in-cell simulations confirmed multiple self-injection of electron bunches into the bubble and their beam acceleration with gradient of 1.5 GeV/cm.

Metrology for sub-Rayleigh-length target positioning in~10^(22)W/cm^(2)laser-plasma experiments

Tight focusing with very small f-numbers is necessary to achieve the highest at-focus irradiances.However,tight focusing imposes strong demands on precise target positioning in-focus to achieve the highest on-target irradiance We describe several near-infrared,visible,ultraviolet and soft and hard X-ray diagnostics employed in a~10^(22)W/cm^(2)laser±plasma experiment.We used nearly 10 J total energy femtosecond laser pulses focused into an approximately1.3-μm focal spot on 5±20μm thick stainless-steel targets.We discuss the applicability of these diagnostics to determine the best in-focus target position with approximately 5μm accuracy(i.e.,around half of the short Rayleigh length)and show that several diagnostics(in particular,3ωreflection and on-axis hard X-rays)can ensure this accuracy.We demonstrated target positioning within several micrometers from the focus,ensuring over 80%of the ideal peak laser intensity on-target.Our approach is relatively fast(it requires 10±20 laser shots)and does not rely on the coincidence of low-power and high-power focal planes.

Using LiF crystals for high-performance neutron imaging with micron-scale resolution

This paper describes an overview of our recent discovery – clear demonstration that Li F crystals can be efficiently used as a high-performance neutron imaging detector based on optically stimulated luminescence of color centers generated by neutron irradiation. It is shown that the neutron images we have obtained are almost free from granular noise, have a spatial resolution of～5.4 μm and a linear response with a dynamic range of at least 103. The high contrast and good sensitivity of Li F crystals allow us to distinguish two holes with less than 2% transmittance difference. We propose to use such detectors in areas where high spatial resolution with high image gradation resolution is needed, including diagnostics of different plasma sources such as laser and z-pinch produced plasmas.

MeV-and Sub-MeV-photon Sources Based on Compton Backscattering at SPring-8 and KPSI-JAEA

Recently we have constructed two facilities for generating photon beams in the MeV and sub-MeV energy regions by means of the Compton backscattering with a laser and an electron beam at SPring-8 and at Kansai Photon Science Institute of Japan Atomic Energy Agency(KPSI-JAEA). The MeV-photon source at SPring-8 consists of a continuous-wave optically-pumped far infrared laser with a wavelength of 118.8 μm and an 8 GeV stored electron beam. Present MeV-photon flux is estimated to be 1.3×103 photons/s. On the other hand,the sub-MeV-photon source at KPSI-JAEA consists of a pulse Nd∶YAG laser with a wavelength of 1 064 nm and a 150 MeV electron beam accelerated by microtron. In the first trial of the photon production in this source,backscattered photon flux is estimated to be 20 photons/pulse. Both the Compton backscattered photon sources have possibilities to be used for new tools in various fields such as nuclear physics,materials science,and astronomy.