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The characteristics of an accelerator using the inverse free electron laser process [1,2] are investigated by a 1D FEL simulation code in order to clarify the potential of this type of accelerator. The instability by the finite spectral width of the laser light is also investigated. Further, the energy losses by higher harmonics and by synchrotron radiation are studied.

A spatial structure of porous silicon formed by anodization was simulated using a lattice model considering the quantum confinement effect. Calculation starting from a random distribution of null cells at the surface yielded the final granular, columnar or flat surface structures depending on the magnitude of the anodizing bias voltage in concordance with previously reported structures. Our calculations suggest that columnar and dendritic structures can be produced in degenerately doped p-type Si wafers by self-organization of nanowires with quantum confinement effects.

We have been developing a coherent "white light" lidar using a terawatt laser system at 800 nm with a 9m length krypton gas cell, which emits a coherent supercontinuum from UV to near infrared regions. Linearly polarized supercontinuum was transmitted to the atmosphere, and backscattered light was collected with a telescope of 31.8 cm in a diameter and the light was separated into 3 to 5 wavelengths using dichroic mirrors and interference filters. Mainly, we used the wavelengths of 450, 550, 700nm and 800 nm with each bandwidth of 10 to 40 nm. Although, the energy of light included in each wavelength range is restricted, the advantage of multi-spectral features on the same optical axis of this system enables us to use preferred spectral lines for various measurements. The system was successfully applied as a depolarization lidar as well as a multi line Mie scattering lidar for cloud particles and Aeolian dusts. By comparing the response for each spectrum, we can determine the size of particles with information on their shapes. Current research is focused to find applications in near infrared region of the white light.

A series of laser fusion implosion experiments of plastic hollow shell targets was performed by using the Gekko XII glass laser in order to achieve the required fuel areal density for ignition. Introducing random phase plates to improve illumination uniformity, high-density compression of more than 600 times deuterium liquid density has been achieved. The implosion dynamics and symmetry were observed with a spatially resolved x-ray streak camera and an x-ray multiframing camera. The three-dimensional emission profile of the laser-heated plasma was reconstructed from the x-ray images by use of computed tomography and was compared with the laser illumination profiles. The areal density of the imploded core was measured by the neutron activation of a silicon tracer, the secondary reaction method, and the knock-on proton method. Although the measured density and areal density were consistent with those from 1-D hydrodynamic simulation, experimental neutron yields were significantly lower than those predicted by the simulation for convergence ratios larger than 20. This suggests that better implosion uniformity is required to create a hot spark.

The electron dynamics in the inverse FEL accelerator is investigated by a 1D FEL simulation code. The electron bunch length in acceleration buckets and the trapping fraction are found to vary when the gradient of wiggler field tapering is changed. When an infrared laser of 60 GW is focused to a 200 μm diameter laser spot, the maximum acceleration rate reaches 100 MeV/m and the bunch length is about 1 15 of the laser wavelength. As a realistic case study, FInite bandwidth of the laser field has to be taken into account. The critical bandwidth is found to be approximately a betatron oscillation frequency.

Planer stripe and foil targets coated with NaF were irradiated with high intensity 351 nm laser radiation of 130 ps duration. Time-integrated as well as time-resolved measurement of gain on NaXIHα at 54.2A were made. A time-integrated gain of 1.2−1.1+0.8cm−1 and a time-resolved peak gain of 3.2±1.0 cm−1 were obtained. A detailed account of the experimental procedures for determination of gain is given.

A hydrocarbon ablator was uniformly deposited by means of laser‐induced chemical vapor deposition (CVD) onto a spherical glass microsphere target, which was levitated by a viscous gas jet flow. The maximum deposition rate was 18.4 nm/min and the uniformity of the coating layer was 98%. The deposition rate was independent of the back pressure ranging from 1×10−2 to 2×104 Pa. The deposition rate increased with the flow rate of the coating gas and with the laser intensity irradiating the microsphere. Optimum condition of the gas flow for stable levitation is also suitable for laser‐CVD coating. These characteristics are preferable to coatings on future targets of larger sizes. Characterizations of the coating layer obtained in this work with a scanning electron microscope, a contact x‐ray microradiograph, and an optical interference microscope are presented.

Inertial confinement fusion (ICF) has made great progress. In fact several significant scientific firsts have been achieved in the last year. These developments have presented the ICF community with an opportunity to embark on a new phase in ICF research. The key issues of laser fusion are to attain a high absorption of laser light in a plasma, to prevent preheating of fuel during the compression, and to achieve highly efficient implosion by uniform compression of fuel due to the homogeneous deposition of laser energy on the pellet surface. Direct drive and indirect drive have been investigated. The progress in both schemes is remarkable. The neutron yield by the stagnation free compression of the LHART target has attained 1013 which corresponds to a pellet gain of 1/500. The plastic shell target has reached a fuel density as large as 600 times the liquid density which is measured by the Si activation method as well as the D knockon method. A cryogenic foam target is now under investigation.

Laser oscillations with nearly diffraction limited output beam of a copper vapor laser (CVL) were investigated. The beam divergence less than 0.3 mrad in the pulse duration of 75ns was attained by the long pulse excitation. Also, good beam quality in the whole pulse duration was obtained by the injection locking, with the threshold injection power of only 0.1 W. The CVL beam quality has been successfully established for the master oscillator power amplifier.

Phase transition (amorphization and crystallization) of Si by ultrashort pulse laser irradiation is reported in this paper. We investigated the dependences of ablation rate and fluence for amorphization on laser pulse width.

In this paper, application of white light lidar system for the multi-wavelength depolarization measurement of clouds and aerosols will be presented. The new lidar system consisted of three depolarization channels at 450, 550 and 800 nm. The linear depolarization ratio (delta = S/P) at 450 nm can be seen to increase with increasing cloud depth due to the multiple scattering.

The development of an intense and coherent light source is expected in the X-ray region, because of its many applications in this region. But it is difficult to obtain such a short wavelength with ordinary FEL using the resonator and conventional laser. SASE FEL without the resonator is a promising scheme due to the improvement of accelerator technology. The high power FEL in the 2—4 nm range has already been proposed at SLAC [1,2]. The quasi-stable optical klystron [3,4] can reduce the wiggler length significantly for a soft x-ray SASE FEL. According to the numerical study the gain curve of the quasi-stable optical klystron has multiple gain peaks with narrow width and high gain. Fig. 1a shows the gain curve of the quasi-stable operation of the optical klystron and modulated energy distribution of the electron beam coupling to the positive gain peaks. Fig. 1b represents the gain curve of the uniform wiggler. When the energy spread of an electron beam is larger than a gain peak, the FEL gain becomes very low due to the negative gain of the gain function. But if the distribution of electron energy is modulated and its modulation peaks couple to the positive peaks of the optical klystron gain function, we can obtain the high FEL gain although the total energy spread of the electron beam is large. With the latest technology of laser pulse shaping, it is possible to produce femtosecond pulses [5,6]. This pulse shaping apparatus called liquid crystal spatial light modulator (LC SLM). Two LC SLMs are combined between a pair of polarizes. When the LC modulator is operated by applying a voltage, the liquid crystals rotate towards the direction of propagation of light and produce the modified pulses. With this apparatus, the user can specify the waveform with arbitrary profiles. When the modulated laser that is obtained in this way irradiates the photocathode, the modulated electrons are extracted with the same temporal profile, because the response time of metal photocathode is of femtosecond order. This is a very important property of our concept. This is the advanced operation of quasi-stable optical klystron with energymodulated electron beam. The electrons extracted with temporal modulation are accelerated with an RF gun. Then these electrons are accelerated in different RF phases.

We have developed an integrated Laser Ablation Fluid Radiation simulation Code (LAFRAC) to estimate the behaviors of highly energetic ions and neutral particles from LPP EUV light sources, and estimated recombination and charge transfer processes between the particles from laser-produced Xe EUV light sources. We clarify that charge transfer effects greatly affect on the number density of neutral particles, especially high energy (more than roughly 500 eV) neutral particles.

The intensity of broad quartet signal often identified as methyl radical (·CH 3 ) in alkali feldspars is enhanced by γ-irradiation. The average g factor and hyperfine A of the broad distorted signal are g = 2.0033 and A = 2.45 mT, respectively, and were previously identified as ·CH 3 or ·C 2 H 5 . The intensity of the quartet signal is enhanced by two orders of the magnitude by hydrothermal experiments of Na-feldspars in NH 3 atmosphere and therefore the signal was identified as ·NH 3 + where the anisotropic hyperfine due to N (I = 1) is not observed due to broadening in the powdered spectrum.

A one-dimensional, multi-frequency simulation code has been developed for FELs which use a waveguide to confine the radiation field. Using this simulation code, we analyzed the spontaneous emission from electron micropulses produced by an RF linac. It is found that for some parameters both high and low frequency waveguide modes are growing simultaneously and the resulting spectrum thus contains two peaks. Finally, the experimentally obtained dependence of the radiation power on cavity length detuning is analyzed.

The application of electron spin resonance (ESR) was studied for diesel soot samples and suspended particulate matter (SPM) from automobile engines. Soot samples or diesel exhaust particles (DEP) were recovered at various points: in the exhaust pipe of a diesel engine, at the dust sampler of a highway tunnel (standard DEP), on the soundproofing wall alongside a heavy traffic road, and on the filters of a dust sampler for SPM. The diesel soot samples apparently showed two ESR spectra: one was a broad spectrum at g=2.1 with a line width of ca. 80-120 mT and the other was a sharp signal of a carbon radical at g=2.003 with a line width of 0.4 mT. Annealing experiments with a DEP sample at 250 degrees C revealed drastic enhancement of the sharp ESR signal, which suggested a thermal process of carbonization of remnant organics. An oximetric study by ESR showed an enhancement of the broad signal in the diesel soot sample as well as in the sharp ESR signal. Therefore, the main part of the broad ESR signal would be attributed to carbon radicals, which form a different configuration, probably closely interacting aggregates. Enhancement of the sharp ESR signal was not observed in the standard DEP sample under vacuum condition, which suggested less adsorption sites on the surface of DEP samples.

In this paper, application of white light lidar system for the multiwavelength backscatter measurements of clouds and aerosols will be presented. The white light continuum was generated by a focused 0.8 TW/100 fs laser pulse in a 9-m long gas cell filled with atmospheric krypton rare gas, which generated a broad spectrum of the white light. We observed the temporal evolution of the backscattered coefficient and analyzed the particle size distribution.

Extreme ultraviolet (EUV) emission from laser produced plasma attracts much attention as a next generation lithography source. The characterization of EUV emission has been carried out using GEKKO XII laser system. The twelve beams irradiated tin or tin-oxide coated spherical targets uniformly and dependence of EUV spectra on laser intensity were obtained with a transmission grating spectrometer and two grazing incidence spectrometers. The EUV Conversion Efficiency (CE, the ratio of EUV energy at the wavelength of 13.5 nm with 2 % bandwidth to incident laser energy) was measured using an absolutely calibrated EUV calorimeter. Optimum laser intensities for the highest conversion were found to be 0.5- 1x10 11 W/cm 2 with CE of 3 %. The spectroscopic data indicate that shorter wavelength emission increases at higher laser intensities due to excessive heating beyond optimum temperatures (20- 40 eV). The CE was almost independent on the initial coating thickness down to 25 nm.

Using a one-dimensional multi-frequency simulation code, we have investigated how the radiation build-up time in an FEL oscillator depends upon the electron beam micropulse width and micropulse shape. From the simulation, it is found that in the Gaussian electron beam case when the electron beam micropulse width is shorter than the radiation wavelength, the radiation in the cavity builds up faster than in longer cases (because of the coherent spontaneous emission). But in the square electron beam pulse case, the spontaneous emission at the edge is much stronger than in the case of a Gaussian electron beam pulse, so the effect of coherent spontaneous emission is reduced. The radiation spectral intensity and temporal profiles have been evaluated for super Gaussian pulse shapes of a bunched electron beam.

An ESR (electron spin resonance) study was made on radiation induced defects in synthetic coesite and stishovite, high pressure phases of SiO 2 . Samples were synthesized in a static condition from SiO 2 glass with high purity, and was irradiated with γ-rays. In coesite, an axial signal with g ∥ = 2.0027 and g ∥ = 1.9993 and an orthorhombic one with g zz = 2.0004, g yy = 1.9993 and g xx = 2.0048 are compared with those of defects in ZrSiO 4 . Two nonequivalent oxygen sites in coesite would be associated with these signals. In stishovite, only an axial signal with g ⊥ = 2.0052 and g ∥ = 2.0023 is detected, probably due to oxygen vacancy centers.

A compact FEL system is developed at ILT/ILE, Osaka, Japan. The wavelength range from mm to several μm in infrared and soft X-ray generation using a laser undulator is expected.

Summary form only given. Highly uniform implosions are important to realize the ignition in inertial confinement fusion. A substantial improvement of irradiation uniformity has been performed by replacing coherent laser beams with partially coherent light (PCL). Because the, PCL has speckle structure in the near field it causes small scale self-phase modulation resulting in spectral broadening and self-focusing in the high power operation regime. Therefore, we should, determine an operation level of the PCL to prevent optics from light-induced damage which has been observed recently in disk-type glasses at the end of amplifier chains. These filamentary bulk damages are likely to be due to the self-focusing of the PCL beam of 2 GW/cm/sup 2/ (average intensity) with a 0.6-nm bandwidth. Calculations of PCL propagation have been performed to compare with these experimental results.

Summary form only given. In the past few years, people recognized it is possible to amplify broadband optical pulses through optical parametric process with a few of well-developed nonlinear crystals. However direct amplification of the femtosecond pulses is limited by their pulse duration and associated nonlinear effects. We present both simulation and experimental studies on a stable high gain OPCPA (optical parametric chirped-pulse amplification) system which may be used as a preamplifier to replace the current complicated regenerative system and multi-pass Ti:sapphire amplifiers especially working at 1 /spl mu/m.

A case of overexposure of an industrial radiographer using 192Ir sources and having a filmbadge dosimeter record of 104 mSv has been examined with ESR dosimetry of postmortem tooth and bone specimens. ESR measurements of the tooth enamel showed an intense signal of CO2- and gave the equivalent dose (ED) of 14 Gy by the additive dose method using gamma-rays from a source of 60Co. The doses for a finger bone and humerus were 14.7 and 7.0 Gy, respectively. It was concluded that he had been exposed to radiation repeatedly over 10 yr and that ESR dosimetry can give a life-long cumulative dose for personnel using radiation.

Key issues of light‐ion‐beam fusion research are an improvement of beam divergence and a demonstration of target heating to achieve an intense and uniform soft x‐ray radiation in the Hohlraum. A two‐stage diode is proposed and demonstrated to reduce the beam divergence on Reiden‐SHVS, an eight‐stage induction adder accelerator. The two‐stage diode is only an active method to reduce the beam divergence. Divergences of carbon beam at the first and the second stage diode were measured by shadow‐boxes. The results show that the divergence improvement agrees with prediction until the current density is less than about 5 times of the space charge limited value. On an annular two‐stage proton diode, a distribution of radial and azimuthal beam divergence were measured simultaneously by 2‐dimensional arrayed pinhole camera. The results show that the azimuthal divergence was larger than the radial one.

An ion beam of about 700 keV Carbon and Proton, about 20 A/cm2 Ji, from an applied‐B two stage diode driven by Reiden‐SHVS induction adder system of 4 (2+2) MV, 160 GW, 100 ns capability, are measured by using two‐dimensional APC with time resolved detector. We optimize beam uniformity by changing the magnetic field of the diode. A beam uniformity improvement is achieved at uniform‐B pressure condition of diode magnetic field. Divergence in parallel and perpendicular direction are measured individually. Different dependence on This measuring system has time resolution of 10 ns, 1 mm spatial resolution on the anode of diode and about 10 mrad processed divergence resolution.

A computer simulation code to treat atomic excitation and laser beam propagation simultaneously in an atomic laser isotope separation system has been developed. The three- level Bloch-Maxwell equations are solved numerically to analyze the change of pulse shapes, the modification of laser frequencies and the time-varying atomic populations. The near- resonant effects on the propagation of frequency chirped and non-chirped laser pulses have been analyzed. It was found that there are serious differences in pulse shapes, frequency modifications and propagation velocities between laser pulses with and without chirping.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The propagation of a radiation heat wave through a thin foil of solid gold was investigated experimentally. The wave is driven by the intense thermal radiation in 1--3-mm-diam gold cavities heated by an intense laser pulse (duration 0.8--0.9 ns, wavelength 0.35 \ensuremath{\mu}m) to temperatures ranging from 80 to 240 eV. Evidence of the propagating wave was obtained from the delayed onset of thermal emission from the outer side of the foil. A detailed comparison of the results with the self-similar solution for the ablative heat wave and with numerical simulations is presented.

High density compression of over 600 times solid density has been achieved by the laser implosion of a hollow shell pellet of deuterated and tritiated plastics (CDT). This is the highest density of material which has ever been realized in a laboratory and corresponds to the density four times higher than the center of the sun.

Lidar (light detection and ranging) depolarization measurements were performed simultaneously at three wavelengths using a coherent white light continuum. The white light continuum ranging from the ultraviolet to the infrared region was generated by a focused 0.5 TW/100 fs pulse in a krypton gas cell at the atmospheric pressure. The lidar system consisted of three depolarization channels at 450, 550, and 800 nm. The observed depolarization ratios for each wavelength showed differences for clouds. These depolarization features in wavelength are discussed in terms of particle size and shape using T-matrix computations. The depolarization ratios at three wavelengths can be used to infer information on the size of the particles in clouds, assuming an ice crystal shape a priori. Also, the obtained size distributions from the three-wavelength depolarization ratios correspond with the changes in particle size indicated by changes in the Angstrom coefficient obtained by multiwavelength lidar techniques. This stud...