Advanced Photon Research Center Research Articles

Nonlinear Thomson scattering with strong radiation damping

With the advent of high-intensity short pulse lasers it has become possible to achieve extremely high intensities. When such laser pulses interact with plasmas or high-energy electron beams, radiation damping, which is usually small, can become large. We examine the effects of radiation damping on the backscattered Thomson radiation numerically and analytically. Using parameters comparable to the laser and microtron at the Advanced Photon Research Center we find that the overall spectrum is down-shifted and that the overall amplitude of the radiation is smaller than in the case with no damping.

Generation and characterization of electrons from a gas target irradiated by high-peak-power lasers

We present the results of electron generation experiments conducted at the Advanced Photon Research Center, Japan Atomic Energy Research Institute, using 23-fs relativistically intense 20-TW tightly focused laser pulses with underdense plasma. We observed electron energies up to 40 MeV characterized by a two-temperature Maxwell distribution. With the help of particle-in-cell simulations, we found that these are due to different plasma wave-breaking processes. A charge of 5 nC/shot was obtained at a small solid angle, which corresponds to high peak current generation.

Observation of strongly collimated proton beam from Tantalum targets irradiated with circular polarized laser pulses

High-energy protons are generated by focusing an ultrashort pulsed high intensity laser at the Advanced Photon Research Center, JAERI-Kansai onto thin (thickness <10 μm) Tantalum targets. The laser intensities are about 4 × 1018 W/cm2. The prepulse level of the laser pulse is measured with combination of a PIN photo diode and a cross correlator and is less than 10−6. A quarter-wave plate is installed into the laser beam line to create circularly polarized pulses. Collimated high energy protons are observed with CH coated Tantalum targets irradiated with the circularly polarized laser pulses. The beam divergence of the generated proton beam is measured with a CR-39 track detector and is about 6 mrad.

Designing and building an integrated target chamber system for high intensity short-pulse laser-target interaction experiments

We have recently designed and are building a plasma experiment chamber system for a high intensity short pulse Ti:sapphire 100 TW laser (λ=800 nm, 2 J, 20 fs) at the Advanced Photon Research Center, JAERI. The expected primary use of the chamber is for high intensity (up to 1020 W cm−2) laser solid target experiments for hot electron, ion, and x-ray production. In order to achieve these intensity levels, the focal spot size on the target needs to be much smaller (⩽φ10 μm) than those used in relatively high laser energy experiments using ⩾100 fs laser pulse widths. The system consists of a target monitor system, a target insertion device (manipulator shuttle), a target stage assembly, and an on-target beam profiler all integrated together. We used calibrated apertures, hereafter called “zero pinholes,” placed at the focal point to assess the on-target energy accurately within a defined spot area. It is intended for general experiments rather than specifically configured ones, e.g., time-diffraction kind of experiments. However, great care was taken to have the capability to accommodate these types of experiments in the future.

X-ray laser development at Advanced Photon Research Center

Overall activity at the Advanced Photon Research Center is reviewed, with emphasis on x-ray laser program. A 15-TW Nd:glass CPA laser has been developed for x-ray laser experiments. In the preliminary experiments on the transient collisional excitation x-ray laser, a gain of 14 cm 4 has been obtained at 11.9 nm with the Ni-like Sn ions by a short (1-ps) prepulse irradiation. Approaches toward improving x-ray laser coherence by high-harmonics amplification and extending to shorter wavelengths by using thin foil targets are described.

Prospects of High-Field Science.

Electrons as well as ions are accelerated to high energy by extremely high pressure generated with intense optical field at the focus of ultrashort pulse high power lasers. Even relativistic ions couldbe generated at the intensity close to 1025 W/cm2. Development of ultra-compact accelerators and high brightness x-ray sources with T-cube lasers (table-top TW lasers) at the Advanced Photon Research Center are described.

Japan Pumps Up Budget for Table-Top Short-Pulse Lasers

Tokyo—Japan is thinking small in science—on a grand scale. The goal is to squeeze the capabilities of high-power lasers into a new generation of lasers that can fit on a table top. A $100 million a year project is gearing up to build an Advanced Photon Research Center that will extend the abilities of short-pulse lasers and turn them into new tools for accelerating particles, creating x-ray holograms of living cells, and exploring ultrahigh-speed phenomena.