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Fast neutrons were generated from a deuterated polystyrene (C8D8) solid-target irradiated by a high-intensity laser. A TOF neutron signal is analyzed in detail. A neutron yield of 1206 n/pulse is estimated from a CR-39 neutron detection, and a maximum deuterium ion energy of 76 keV is measured from a Faraday cup signal. The employed laser has a 27-fs pulse width and a 260-mJ pulse energy.

We have numerically and experimentally verified that the sequence of optical elements in a femtosecond Ti:sapphire laser affects the output spectrum. With the same net dispersion in a cavity, the width and the shape of output spectrum was significant changed when the sequence of dispersive elements was changed in a Kerr-lens mode-locked Ti:sapphire laser with fused-silica prisms. We also showed that the dynamics of pulse formation can be affected by the output coupler's position though the combined action of output coupling and self-phase modulation. Such phenomena can be explained based on pulse formation in a laser cavity with discrete distribution of dispersion and self-phase modulation.

We have numerically and experimentally investigated the characteristics of the optical parametric chirped-pulse amplification (OPCPA) of femtosecond Ti:sapphire laser pulses by using BBO crystals. Numerical calculations showed that a high gain and a broad gain bandwidth could be obtained with a 532-nm pump laser. The dependence of the gain profile of OPA on phase matching angles, pump intensity, and crystal length was numerically investigated. Experimental results showed that the broadband amplification of femtosecond Ti:sapphire laser pulses could be realized by OPCPA and that the temporal fluctuation of a pump laser resulted in the modulation of amplified spectra in OPCPA.

We report the experiment conducted on the Prague Asterix Laser System (PALS) laser facility dedicated to make a parametric study of the laser-plasma interaction under the physical conditions corresponding to shock ignition thermonuclear fusion reactions. Two laser beams have been used: the auxiliary beam, for preplasma creation on the surface of a plastic foil, and the main beam to launch a strong shock. The ablation pressure is inferred from the volume of the crater in the Cu layer situated behind the plastic foil and by shock breakout chronometry. The population of fast electrons is analyzed by Kα emission spectroscopy and imaging. The preplasma is characterized by three-frame interferometry, x-ray spectroscopy and ion diagnostics. The numerical simulations constrained with the measured data gave a maximum pressure in the plastic layer of about 90 Mbar. © 2014 The Royal Swedish Academy of Sciences.

We report three dimensional numerical simulations of a Zeeman slower system with two level atoms. We choose the magnetic field intensity distribution from experimental data and atomic conditions from population analysis of the transitions between F=2 and F=3 lines of the Na atom. We use the Monte-Carlo method for simulation. We generate three kinds of random numbers to specify the initial velocity of the atoms and one more random number for the event of the spontaneous emission. We treat the stimulated emission with numerical solution of the Bloch equation for two level atoms. We put atoms into the Zeeman slower system one by one and follow the motion of each atom. Two forces are considered; one is the intensity gradient force caused by stimulated emission and the other is the divergence force caused by spontaneous emission. We employ a parameter related with the atomic states at the exit port of the Zeeman slower. This parameter is related with space distribution and the velocity distribution of the atom at the exit. We analyze threekinds of the laser beam conditions; one is the focusing condition, another being intensity conditions and the last one being intensity shape conditions of the laser beam front.

We show that optimal detuning method describing population transfer passage in a three‐level system has an essential difference from the adiabatic following passage by counterintuititive sequence of two coherent laser pulses, by examining the dressed eigenstates and the Bloch vector precessing around a torque vector. In a four‐level Λ system, population dynamics is studied for the case where, on the optimal detuning condition, two‐photon coherences causing adiabtic transfer interfere each other. For a scheme of three degenerate levels, we show a possibility of complete population inversion by the optimal detuning method.

Interactions of high-intensity femtosecond lasers with deuterium clusters leading to Coulombic explosions and subsequent production of fusion neutrons attracted in recent years considerable attention. In order to maximize the neutron yield finding a dependence of clusters size and their spatial distribution on experimental conditions became very important. In this paper a possibility to measure the deuterium clusters spatial distributions experimentally was analyzed. In combination with experiments recently performed in the Laboratory of Quantum Optics at the Korea Atomic Energy Research Institute (KAERI) interferometry was identified as the diagnostics suitable for such measurements.

Laser produced plasma is one of the brilliant x-ray source that has unique capabilities for use in a wide range of science. Here we describe two examples of laser-produced plasma x-ray source application; one is for the semiconductor device industry and the other is for the astronomy. Extreme ultraviolet (EUV) light sources for microlithography are receiving much attention as an industrial application of laser-produced x-ray source. High power and clean EUV light source, 13.5 nm of wavelength, is developed for mass-production of next generation semiconductor devices. Highest EUV conversion efficiency of 4% has been attained by using low-density and minimum-mass tin targets produced by laser-driven explosion of micro-droplet. In addition, it was recently demonstrated that laser-produced x-ray source is very useful to simulate x-ray astronomical phenomena in the laboratory. A 0.5-keV Planckian x-ray source was created with laser driven implosion for producing non-local-thermodynamical-equilibrium (non-LTE) photoionized plasmas, which is a key to understand astronomical compact objects. Laboratory experiment of non-LTE photoionized plasma offers novel test bed for validation and verification of computational codes used in x-ray astronomy.

Photo-ionized silicon plasma was studied using 500-eV Planckian radiation from implosion core plasma generated with Gekko-XII laser to simulate a astrophysical photo-ionized plasma. Three major features were observed in an energy range from 1.80 to 1.88 keV and origins of the features were replicated with a time-dependent collisional-radiative model including photo-ionization processes: The line at 1.865 keV is the resonance line by inner-shell photo-ionization of Li-like Si ions and that at 1.840 keV is the sum of satellite lines attributed to the inner-shell photo-ionization of Be-like ions. Emission lines in the soft x-ray/extreme ultra-violet (EUV) region (i.e., 140 to 300 eV) from the low-temperature Si plasma in prior to the photo-ionization were also identified to extract the intial temperature and density of the pre-formed Si.

A novel efficient scheme of acceleration and collimation of dense plasma is proposed and examined. In the proposed scheme, a target placed in a cavity at the entrance of a guiding channel is irradiated by a laser beam introduced into the cavity through a hole and accelerated along the channel by the pressure created and accumulated in the cavity by the hot plasma expanding from the target and the cavity walls. Using 1.315-um, 0.3-ns laser pulse of energy up to 200J and a thin CH target, it was shown that the forward accelerated dense plasma projectile produced from the target can be effectively guided and collimated in the 2-mm cylindrical guiding channel and the energetic efficiency of acceleration in this scheme is an order of magnitude higher than in the case of conventional ablative acceleration., Comment: 4 pages, 6 figures

Photoionized plasmas are encountered in astrophysics wherever low-temperature gas/plasma is bathed in a strong radiation field. X-ray line emissions in the several kiloelectronvolts spectral range were observed from accreting clouds of binary systems, such as CYGNUS X-3 and VELA X-1, in which high-intensity x-ray continua from compact objects (neutron stars, black holes or white dwarfs) irradiate the cold and rarefied clouds. X-ray continuum- induced line emission accurately describes the accreting clouds, but experimental verification of this photoionized plasma model is scarce. Here we report the generation of photoionized plasmas in the laboratory under well-characterized conditions using a high-power laser. A blackbody radiator at a temperature of 500 eV, corresponding to a compact object, was created by means of a laser-driven implosion. The emerging x-rays irradiate a low-density (n(e) < 10(20) cm(-3)) and low- temperature (T(e) < 30 eV) silicon plasma. Line emissions from lithium- and helium-like silicon ions were observed from a thermally cold silicon plasma in the 1.8-1.9 keV spectral region, far from equilibrium conditions. This result reveals the laboratory generation of a photoionizing plasma. Atomic kinetic calculations imply the importance of direct K-shell photoionization by incoming hard x-rays.

Energetic ion generation from the interaction of a short laser pulse with a thin overdense plasma accompanied by a preplasma and a rear side plasma gradient is investigated by particle-in-cell simulations. The dynamics of ion acceleration depending on the maximum density of the preplasma in front of the overdense plasma slab with a smooth density gradient at the rear side are presented and discussed by comparing a sharp rear side boundary case.

We have numerically and experimentally verified that the sequence of optical elements in a femtosecond Ti:sapphire laser affects the laser’s characteristics. Even with the same net dispersion in a cavity, the output spectrum showed a significant change in width and shape when the sequence of dispersive elements was changed in a Kerr-lens mode-locked Ti:sapphire laser with fused-silica prisms for dispersion compensation. It was also shown that the output coupler’s position can affect the dynamics of pulse formation by the combined action of output coupling and self-phase modulation. We explain such phenomena based on pulse formation in a laser cavity with discrete distribution of dispersion and self-phase modulation.

Experiments of photoionized plasmas and shock wave generation, which are related to laboratory astrophysics, have been performed with the Shengguang II laser facility. Some preliminary results are presented in this paper.