Masato Kanasaki

Proton acceleration to 40 MeV using a high intensity, high contrast optical parametric chirped-pulse amplification/Ti:sapphire hybrid laser system.

Using a high-contrast (10(10):1) and high-intensity (10(21) W/cm(2)) laser pulse with the duration of 40 fs from an optical parametric chirped-pulse amplification/Ti:sapphire laser, a 40 MeV proton bunch is obtained, which is a record for laser pulse with energy less than 10 J. The efficiency for generation of protons with kinetic energy above 15 MeV is 0.1%.

Acceleration of highly charged GeV Fe ions from a low-Z substrate by intense femtosecond laser

Almost fully stripped Fe ions accelerated up to 0.9 GeV are demonstrated with a 200 TW femtosecond high-intensity laser irradiating a micron-thick Al foil with Fe impurity on the surface. An energetic low-emittance high-density beam of heavy ions with a large charge-to-mass ratio can be obtained, which is useful for many applications, such as a compact radio isotope source in combination with conventional technology.

High-Contrast, High-Intensity Petawatt-Class Laser and Applications

A high-contrast high-intensity petawatt-class Ti:sapphire chirped-pulse amplification laser has been developed for research on high field science. A saturable absorber and a low-gain optical parametric chirped-pulse amplification preamplifier in the front-end have improved the temporal contrast in the system to ∼

Nonlinear increase of X-ray intensities from thin foils irradiated with a 200 TW femtosecond laser

2 \times 10^{12}

Characterization of submicron-sized CO2 clusters formed with a supersonic expansion of a mixed-gas using a three-staged nozzle

on the subnanosecond time scale at the ∼70 TW power level. In addition to the high-contrast broadband high-energy output from the final amplifier has been achieved with a flat-top spatial profile with a filling factor of ∼70%. This is the result of pump beam spatial profile homogenization with diffractive optical elements. The system produces the uncompressed output pulse energy of 29 J, indicating the capability for reaching a peak power of ∼600 TW. We discuss in detail the design, performance, and characterization of the laser including output power, pulse duration, and spatiotemporal beam quality. We also describe the on-going upgrade of the laser system and some applications for the laser in relativistic dominated laser–matter interactions.

Mie scattering from submicron-sized CO 2 clusters formed in a supersonic expansion of a gas mixture

We report, for the first time, that the energy of femtosecond optical laser pulses, E, with relativistic intensities I > 1021  W/cm2 is efficiently converted to X-ray radiation, which is emitted by “hot” electron component in collision-less processes and heats the solid density plasma periphery. As shown by direct high-resolution spectroscopic measurements X-ray radiation from plasma periphery exhibits unusual non-linear growth ~E4–5 of its power. The non-linear power growth occurs far earlier than the known regime when the radiation reaction dominates particle motion (RDR). Nevertheless, the radiation is shown to dominate the kinetics of the plasma periphery, changing in this regime (now labeled RDKR) the physical picture of the laser plasma interaction. Although in the experiments reported here we demonstrated by observation of KK hollow ions that X-ray intensities in the keV range exceeds ~1017  W/cm2, there is no theoretical limit of the radiation power. Therefore, such powerful X-ray sources can produce and probe exotic material states with high densities and multiple inner-shell electron excitations even for higher Z elements. Femtosecond laser-produced plasmas may thus provide unique ultra-bright X-ray sources, for future studies of matter in extreme conditions, material science studies, and radiography of biological systems.

Approaching the diffraction-limited, bandwidth-limited Petawatt

The size of CO2 clusters, produced in a supersonic expansion of a mixed-gas of CO2/He or CO2/H2 through a three-staged conical nozzle designed based on the Boldarevs model, has been evaluated by measuring the angular distribution of light scattered from the clusters. The data are analyzed utilizing the Mie scattering theory, and the sizes of CO2 clusters are estimated as 0.22 μm and 0.25 μm for the cases of CO2/He and CO2/H2 gas mixtures, respectively. The results confirm that the Boldarevs model is reliable enough for the production of micron-sized clusters.

Applicability of Polyimide Films as Etched-Track Detectors for Ultra-Heavy Cosmic Ray Components

A detailed mathematical model is presented for a submicron-sized cluster formation in a binary gas mixture flowing through a three-staged conical nozzle. By measuring the angular distribution of light scattered from the clusters, the size of CO(2) clusters, produced in a supersonic expansion of the mixture gas of CO(2)(30%)/H(2)(70%) or CO(2)(10%)/He(90%), has been evaluated using the Mie scattering method. The mean sizes of CO(2) clusters are estimated to be 0.28 ± 0.03 μm for CO(2)/H(2) and 0.26 ± 0.04 μm for CO(2)/He, respectively. In addition, total gas density profiles in radial direction of the gas jet, measuring the phase shift of the light passing through the target by utilizing an interferometer, are found to be agreed with the numerical modeling within a factor of two. The dryness (= monomer/(monomer + cluster) ratio) in the targets is found to support the numerical modeling. The apparatus developed to evaluate the cluster-gas targets proved that our mathematical model of cluster formation is reliable enough for the binary gas mixture.

Thresholds of Etchable Track Formation and Chemical Damage Parameters in Poly(ethylene terephthalate), Bisphenol A polycarbonate, and Poly(allyl diglycol carbonate) Films at the Stopping Powers Ranging from 10 to 12,000 keV/µm

J-KAREN-P is a high-power laser facility aiming at the highest beam quality and irradiance for performing state-of-the art experiments at the frontier of modern science. Here we approached the physical limits of the beam quality: diffraction limit of the focal spot and bandwidth limit of the pulse shape, removing the chromatic aberration, angular chirp, wavefront and spectral phase distortions. We performed accurate measurements of the spot and peak fluence after an f/1.3 off-axis parabolic mirror under the full amplification at the power of 0.3 PW attenuated with ten high-quality wedges, resulting in the irradiance of ~1022 W/cm2 and the Strehl ratio of ~0.5.

Insertable pulse cleaning module with a saturable absorber pair and a compensating amplifier for high-intensity ultrashort-pulse lasers

The track registration property in polyimide Kapton has been examined for heavy ions, including 2.3 GeV Fe and 24 GeV Xe ions. Conventional track formation criteria fail to predict the thresholds of etch pit formation, while a chemical criterion stating that etchable tracks are formed when two adjacent diphenyl ethers are broken in the vicinity of the ions trajectory should be more appropriate. Discriminative detections of ultra-heavy components in cosmic rays, such as Bi, Th, and U ions, are possible by measuring the recorded track length.