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We report on the design and characterization of the plasma mirror system installed on the J-KAREN-P laser at the Kansai Photon Science Institute, National Institutes for Quantum Science and Technology. The reflectivity of the single plasma mirror system exceeded 80%. In addition, the temporal contrast was improved by two orders of magnitude at 1 ps before the main pulse. Furthermore, the laser near-field spatial distribution after the plasma mirror was kept constant at plasma mirror fluence of less than 100 kJ/cm2. We also present the results of investigating the difference and the fluctuation in energy, pulse width and pointing stability with and without the plasma mirror system.
We have experimentally improved the temporal contrast of the petawatt J-KAREN-P laser facility. We have investigated how the generation of pre-pulses by post-pulses changes due to the temporal overlap between the stretched pulse and the post-pulse in a chirped-pulse amplification system. We have shown that the time at which the pre-pulse is generated by the post-pulse and its shape are related to the time difference between the stretched main pulse and the post-pulse. With this investigation, we have found and identified the origins of the pre-pulses and have demonstrated the removal of most pre-pulses by eliminating the post-pulse with wedged optics. We have also demonstrated the impact of stretcher optics on the picosecond pedestal. We have realized orders of magnitude enhancement of the pedestal by improving the optical quality of a key component in the stretcher.
We characterize the electron density distributions of preformed plasma for laser-accelerated proton generation. The preformed plasma of a titanium target 3 μm thick is generated by prepulse and amplified spontaneous emission (ASE) of a high-intensity Ti:sapphire laser and is measured with an interferometer using a second harmonic probe beam. High-energy protons are obtained by reducing the size of the preformed plasma by changing the ASE duration before main pulse at the front side (laser incidence side) of the target. Simulation results with two-dimensional radiation hydrodynamic code are close to the experimental results for low-density region ~4 × 1019 cm−3 at the front side. In the high-density region near to the target surface, the interferometry underestimates the density due to the substantial refraction. The characterization of hydrodynamic expansion with the interferometer and simulation is a useful tool for investigation of high-energy proton generation.
We observed a preformed plasma of an aluminum slab target produced by a high-intensity Ti:sapphire laser. The expansion length of the preformed plasma at the electron density of 3 × 1018 cm−3, which was the detection limit, was around 100 μm measured with a laser interferometer. In order to characterize quantitatively and to control the preformed plasmas, we perform a two-dimensional hydrodynamic simulation. The expansion length of the preformed plasma was almost the same as the experimental result, if we assumed that the amplified spontaneous emission lasted 3.5 ns before the main pulse arrived.
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.
This paper report the ASCA observations of the three brightest persistent X-ray stars near the Galactic Center: an X-ray burster A1742-294, black hole candidate 1E 1740.7-2942, and unclassified source 1E 1743.1-2843. Emission mechanism is briefly discussed based on the new ASCA results.
We present the ASCA/GIS results of the transient source GRO J1744-28, the bursting X-ray pulsar, for the two times observations about one year apart. (the first and the second observations are on Feb.27th 1996 and Mar.16th 1997 respectively.) Since the discovery of GRO J1744-28 on Dec. 2 1995 with the BATSE observatory (Fishman et al. 1995; Kouveliotou et al.), thousands of Type II X-ray bursts, and sinusoidal pulsations have been observed in the X-ray band. No other source has ever been found to exhibit such unusual characteristics. Following each burst the flux decreases below, and recovers to the pre-burst persistent level (here after the dip) within a few seconds to a few minutes, depending on the total flux of the burst. We examined the spectrum of GRO J1744-28 during each persistent, dip, burst phases at the two observations. This is the first detail study of the spectra (1-10keV band) of GRO J1744-28.
We report the column density distribution to the Galactic Center region using the X-ray binary observations with the X-ray satellite ASCA, and demonstrate a new method of the total mass determination near the Galactic Center. The column densities are given by a simple form as a function of the angular distance from the Galactic Plane. Assuming a disklike mass distribution of 500 pc radius, we estimate the total mass to be ~ 6 × 107M⊙.
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