Yuji Fukuda

Characterization of wave-front corrected 100 TW, 10 Hz laser pulses with peak intensities greater than 1020W∕cm2

An improvement of laser-focused peak intensity has been achieved in a JAERI 100 TW Ti:sapphire chirped-pulse amplifier chain with a feedback controlled adaptive optics system operating at a 10 Hz repetition rate. The Strehl ratio was enhanced to 0.8 by means of a Bimorph deformable mirror with a Shack-Hartmann wave-front sensor. Measurements of optical parameters of the laser pulse and an experimental tunneling ionization yield of helium have practically confirmed focusing to ultrarelativistic intensities of over 1020W∕cm2 within 16% accuracy.

Relativistic laser plasma from micron-sized argon clusters as a debris-free x-ray source for pulse x-ray diffraction

We have demonstrated diffraction from Si(111) crystal using x rays from highly ionized Ar ions produced by laser irradiation with an intensity of 6×1018W∕cm2 and a pulse duration of 30 fs acting upon micron-sized Ar clusters. The measured total photon flux and linewidth in the Heα1 line (3.14 keV) were 4×107photons∕shot∕4πsr and 3.7 eV (full width at half maximum), respectively, which is sufficient to utilize as a debris-free light source for time-resolved x-ray diffraction studies.

X-ray radiation of clusters irradiated by ultrafast, high-intensity laser pulses.

High resolution x-ray emission spectra of plasma created by laser irradiation of rare-gas (Ar, Kr, Xe) clusters have been measured at laser intensities over 1019 W/cm2 and 30-fs pulse duration. To make these measurements possible, in addition to the effort to decrease a prepulse intensity using Pockels cell switches, micron-size clusters were produced using a specially designed conical nozzle. The Boltzmann equation and a detailed collisional radiative model are solved simultaneously as a function of time to model the time integrated x-ray spectra of the transient plasma. The results are quantitatively in good agreement with the experimentally observed x-ray emission spectra of Ar clusters.

A diagnosis of intense ion beam by CR-39 detectors analyzing the back scattered particles

A new diagnosis method has been developed utilizing back scattered particles for high energy intense ion beams. The CR-39 detector mounted on the uniform back-scatterer was irradiated with 4He2+ ions with an energy 25 MeV/n, which is never recorded as etchable track in CR-39. We found that it is possible to diagnose by analyzing the etch pits on the rear surface of CR-39 that directly contacted on the back-scatterers. It turns out that most of etch pits in the rear surface are made by the backscattered particles by investigating the growth pattern of each etch pit with multi-step etching technique. This method allows simple diagnosis of the ion beam profile and intensity distribution in mixed radiation field such as laser-driven ion acceleration experiments.

Current Status and Future Prospects of “J-KAREN” — High Contrast, High Intensity Laser for Studying Relativistic Laser-Matter Interactions

Remarkable progress in recent years with Ti:sapphire chirped-pulse amplification (CPA) technique provides great opportunities for experimental study of laser matter interactions in the relativistic regime focusing petawatt-class laser pulses to intensities up to 10 to 10 W/cm. For most plasma physics research, the use of temporal contrast enhancing technique is required to suppress the unwanted intense prepulses that can generate significant preplasma at the target.

Recent progress in particle acceleration from the interaction between thin-foil targets and J-KAREN laser pulses

From the interaction between the high-contrast (∼more than 1010) 130 TW Ti:sapphire laser pulse and Stainless Steel-2.5 um-thick tape target, proton beam with energies up to 23 MeV with the conversion efficiency of ∼1% is obtained. After plasma mirror installation for contrast improvement, from the interaction between the 30 TW laser pulse and thin-foil target installed on the target holder with the hole whose shape is associated with the design of the well-known Wehnelt electrode of electron-gun, a 7 MeV intense proton beam is controlled dynamically and energy selected by the self-induced quasi-static electric field on the target holder. From the highly divergent beam having continuous spectrum, which are the typical features of the laser-driven proton beams from the interactions between the short-pulse laser and solid target, the spatial distribution of 7 MeV proton bunch is well manipulated to be focused to an small spots with an angular distribution of ∼10 mrad. The number of protons included in the b...

High-Intense, High-Contrast J-KAREN Laser at Advanced Photon Research Center

We demonstrate a compact high-intense, high contrast OPCPA/Ti:sapphire hybrid laser. The 80 TW peak power at 10 Hz repetition rate with ~9 orders temporal contrast in a few picoseconds region was obtained.

Characterization of a 1020 W · cm−2 Peak Intensity by Focusing Wavefront-corrected 100-TW, 10-Hz Laser Pulses

An improvement of laser-focused peak intensity has been achieved in a JAERI 100 TW Ti:sapphire chirped-pulse amplifier chain with a feedback controlled adaptive optics system at a 10 Hz repetition rate. Independent measurements of optical parameters of the laser pulse and an experimental tunneling ionization ratio of He atom with laser energy scaling have practically confirmed an ultrarelativistic intensity of over 1020 W · cm−2.

Super strong field ionization of atoms by 1019 W cm−2, 10 Hz laser pulses

Abstract We report on the optical field ionization of rare gases (argon, krypton and xenon) by > 1019 W cm−2 laser pulses whose electric field well exceeds the Coulombic binding field in strength. Charge states as high as Ar16+, Kr19+, and Xe26+ have been observed, which correspond to He-like argon, Cl-like krypton and Ni-like xenon, respectively. The extension of the laser system to petawatt peak powers is described.