Proceedings Volume 3886

High-Power Lasers in Energy Engineering

Kunioki Mima, Gerald L. Kulcinski, William J. Hogan
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Proceedings Volume 3886

High-Power Lasers in Energy Engineering

Kunioki Mima, Gerald L. Kulcinski, William J. Hogan
View the digital version of this volume at SPIE Digital Libarary.

Volume Details

Date Published: 11 January 2000
Contents: 13 Sessions, 82 Papers, 0 Presentations
Conference: Advanced High-Power Lasers and Applications 1999
Volume Number: 3886

Table of Contents

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Table of Contents

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  • Laser Fusion Review and Laser-Plasma Physics
  • Laser Fusion Technology
  • Fast Ignition and Short-Pulse Laser Interactions
  • Ultra-Intense Laser-Plasma Interactions and Laser Acceleration
  • Laser Acceleration
  • Laser-Triggered Lightning
  • Laser-Triggered Discharge and Laser Isotope Separation
  • Lasers for Energy Engineering
  • X-Ray Lasers
  • X-Ray Lasers and Laser-Plasma X-Ray Sources
  • Laser-Plasma X Rays and Laser Applications
  • Poster Session I
  • Poster Session II
  • Laser Fusion Review and Laser-Plasma Physics
Laser Fusion Review and Laser-Plasma Physics
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Inertial fusion energy development: what is needed and what will be learned at the National Ignition Facility
William J. Hogan
Successful development of inertial fusion energy (IFE) requires that many technical issues be resolved. Separability of drivers, targets, chambers, and other IFE power plant subsystems allows resolution of many of these issues in 'off-line' facilities and programs. Periodically, major 'integrated' facilities give a snapshot of the rate of progress toward the ultimate solutions. The National Ignition Facility (NIF) and Laser Megajoule (LMJ) are just such integrating facilities. This paper reviews the status of IFE development and projects what will be learned from the NIF and LMJ.
Spatial distributions of ions and other particles in laser plasma
Serguei Silnov
A procedure for distinguishing the regions of emission of laser-plasma jet multiply charged ions is developed and realized. With the aid of the procedure, the presence of the transverse emission of laser-plasma jet multiply charged ions is found experimentally and its parameters are studied. The size for the effective region of emission of laser- plasma jet multiply charged ions is determined experimentally. It is found experimentally that the main process leading to the decrease of the multiply charged ion yield for a surface is the nonresonant ion recharge on atoms. Within the model concerned, the spray of multiply charged ions over the surface of a massive sample was predicted and found experimentally.
Laser Fusion Technology
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Electricity production from laser-driven fusion reactors: technological aspects of power conversion chambers
Gerald L. Kulcinski
One of the most important considerations for laser driven fusion power plants is the safe and efficient operation of the chamber that contains the thermonuclear energy released from the target. Several approaches to the design of such a chamber are described in this paper and the critical issues associated with protection of the first wall, the performance of the structural materials, and the cost are discussed. Presently, the need for direct drive illumination of the cryogenic targets makes the use of liquid first wall protection problematical at best. The use of dry first walls protected with a few torr of an inert gas seems to hold the most promise.
Mercury and beyond: diode-pumped solid state lasers for inertial fusion energy
Camille M. Bibeau, Raymond J. Beach, Andy J. Bayramian, et al.
We have begun building the 'Mercury' laser system as the first in a series of new generation diode-pumped solid-state lasers for inertial fusion research. Mercury will integrate three key technologies: diodes, crystals, and gas cooling, within a unique laser architecture that is scalable to kilojoule energy levels for fusion energy applications. The primary performance goals include 10 percent electrical efficiencies at 10 Hz and 100J with a 2-10 ns pulse length at 1.047 micrometers wavelength. When completed, Mercury will allow rep-rated target experiments with multiple target chambers for high energy density physics research.
Development of high-power DPSSL for inertial fusion energy
Yasukazu Izawa, Masanobu Yamanaka, Tadashi Kanabe, et al.
We have conceptually designed a diode-pumped Nd:glass slab amplifier module for Inertial Fusion Energy (IFE). As a first step of a driver development, we have been developing a diode-pumped zig-zag Nd:glass slab laser amplifier system which can generate an output energy of 10 J per pulse at 1053 nm in 10 Hz operation. The water-cooled zig-zag Nd: glass slab is pumped for both sides by 803-nm AlGaAs laser- diode (LD) module; each LD module has an emitting area of 420 mm X 10 mm and two LD modules generated in total 200kW peak power with 2.5kW/cm2 peak intensity at 10 Hz repetition rate. We have obtained in a preliminary experiment a 8.5 J output energy at 0.5 Hz with a beam quality of 2 times diffraction limited far-field pattern.
Fast Ignition and Short-Pulse Laser Interactions
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Production of MeV electrons in a gas-jet target
Kazuyoshi Koyama, Naoaki Saito, Mitsumori Tanimoto
High-energy electrons above 1 MeV are observed from underdense plasmas produced by high power and short laser pulses. The emission of the high-energy electrons seems to have a correlation with an appearance of a complex filamentary structure along the axis of the laser beam. The obtained dependence of the electron energy on the laser power of p(0.7-1.4) and on the gas density of Pgas(1.8-2.3) suggests the presence of the stochastic heating of the electrons.
Lasers for the magnetic configuration control in tokamaks and stellarators
Anatoliy F. Nastoyashchiy, Vladimir D. Pustovitov, Kozo Yamazaki
The possibility of creating magnetic configurations with improved confinement based on the laser ablation of a pellet of frozen hydrogen is considered. The advantageous characteristic of the proposed laser methods is that they allow a local control of the plasma parameters and magnetic field. To solve the above problems, a frozen-hydrogen pellet is injected into the plasma volume and irradiated by laser pulse. As a result of mutual diffusion of laser plasma and magnetic field, some profiles of plasma density and magnetic configuration are realized. It is shown that quasi- stationary equilibrium states of tokamak plasma column sustained by the uninterrupted fuel feeding ca be constructed. It is found that specified profiles of plasma density and magnetic field can be provided by using some plasma particles source whose intensity is determined by the laser flux density.
Ultra-Intense Laser-Plasma Interactions and Laser Acceleration
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Anisotropic filamentation and modulation of ultra-intense linearly polarized laser light in overdense plasma
Katsunobu Nishihara, Tetsuya Honda, Sergei V. Bulanov, et al.
3D particle-in-cell simulations of the interaction of an ultra-intense linearly-polarized laser light with an over- dense plasma are presented. Intense laser radiation is shown to be unstable against modulation both in the direction of the laser propagation direction and in the direction perpendicular to the polarization direction. Growth rate of the instability has a maximum of the order of 0.1(omega) 0 when laser frequency (omega) 0 is of the order of the plasma frequency modified due to the relativistic increase of electron mass in the laser field. As a result the laser breaks up into clumps with the size of the relativistic collision-less skin depth. Analytical description of the instability is also presented. Dependence of the growth rate on the laser intensity and wavenumber of perturbations is discussed.
Proton acceleration in plasma waves produced by backward Raman scattering
Atsushi Ogata, Thomas C. Katsouleas, ShinIchi Masuda
This paper proposes a new method of proton acceleration. A slow plasma wave produced by backward Raman scattering captures slow protons injected. A density gradient of a plasma enables the wave phase velocity to increase as the proton test beams are accelerated. Preliminary results of PIC simulations of the backward scattering are presented in constant and tapered-density plasma. A proof-of-principle experiment is proposed using a T3 laser and test beams from a Van de Graaf accelerator, in which a 500 mJ laser will give acceleration gain of approximately 50MeV in a distance of 500 micrometers .
Self-modulated wakefield excitation in 40-TW laser-plasma and electron acceleration
Yoneyoshi Kitagawa, Michiaki Mori, Yoshihiro Murakami, et al.
Illuminating a 40TW chirped pulse amplified laser on 0.01 critical density hydrogen plasma, we obtain a self-modulated wavefield in the relativistic region, whose amplitude is 24 percent of the average density, or the accelerating field is 160 GV/m. The laser beam is relativistically self-focused, which in turn confined the plasma wave within 0.4 mm diameter over 1 mm axial length. The dephasing distance implies an electron acceleration to 48 MeV, which is consistent with the observation of the averaged energy 35 MeV. Protons of 7 MeV are observed.
Nature of atomic-nuclear processes in intense short laser-matter interaction
Vladimir I. Arefyev, Vadim S. Beliaev
Outlined generally is the nature and model of atomic and nuclear processes in supersolid laser-produced plasmas. In the processes of model development a fundamentally new fusion concept was put forward and substantiated, namely, the photon-field fusion. Our experiments, results of which are described here, substantiated our choice of the line of investigations on the laser produced plasma.
Laser Acceleration
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Laser-based electron acceleration to GeV in free space
Yu-kun Ho, J. X. Wang, Lianghuan Feng, et al.
In this paper, the free-electron scattering by continuous or pulsed laser beams has been investigated in details. It is found that when Q equalsV eE >= 100 an electron can be captured and violently accelerated to GeV energy under proper conditions. From the quantum viewpoint, we can explain this effect on the basis of non-linear and stimulated Comptom scattering. This phenomenon provided us with a new far-field laser acceleration mechanism, whose practical feasibility and application possibility are also discussed.
Measurement of electron density perturbation in laser wakefield
Eiji Takahashi, Keisuke Katsura, Eisuke Miura, et al.
Temporal and spatial electron density oscillation in laser wakefield was measured by Frequency-domain interferometry technique. The period of the plasma oscillation was measured to be 2 THz in the electron density of 5 X 1016 cm-3. In the measurement of radial profiles of electron density oscillation, the expulsion of electrons from the laser axis was apparently observed. These measurement techniques will enables us to perform a coherent control of electron plasma oscillation.
Acceleration of electrons in a vacuum by lasers and the accuracy principle of nonlinearity
Heinrich Hora, M. Hoelss, Werner Scheid, et al.
The new principle of nonlinearity requesting a much higher degree of accuracy of all physical presumptions for the treatment, can be demonstrated ideally by the field of acceleration of electrons by lasers in vacuum. Initially the net energy conversion from electromagnetic radiation to electrons, e.g. by lasers in vacuum, was considered to be impossible based on the fact that plane-wave and phase symmetric wave packets can never transfer energy to electrons apart from Thomson or Compton scattering or the Kapitza-Dirac effect. The nonlinear nature of the electrodynamic forces of the fields to the electrons, expressed as nonlinear forces including ponderomotion or the Lorentz force, however, does permit an energy transfer if the conditions of plane waves in favor of beams and/or the phase symmetry are broken. The result in electron acceleration is now well understood as 'free wave acceleration', as 'ponderomotive scattering', as 'violent acceleration' or as 'vacuum beat wave acceleration'. The basic understanding of these phenomenon, however, relates to an accuracy principle of nonlinearity for explaining numerous discrepancies on the way to the mentioned achievement of 'vacuum laser acceleration'. From mathematically designed beam conditions, an absolute maximum of electron energy per laser interaction has been established. Numerical results strongly depend on the accuracy of the used laser fields for which examples are presented and finally tested by a criterion of the absolute maximum.
Laser-Triggered Lightning
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Tests of laser-induced discharge of high dc voltage using high-power femtosecond UV pulses
Jean-Claude M. Diels, Patrick Rambo, Jens Schwarz, et al.
Pulses of 500 fs or greater duration and several tens of millijoules at 248 nm are used to trigger discharges in air. We will discuss the influence of beam geometry, the minimum field strength that can be triggered, and the electrical discharge guiding properties. The latest measurements have concentrated on DC discharges in air at up to 200 kV. Thanks to a new technique of background free, single shot interferometry, 2D snapshots of the evolving plasma can be recorded. This will lead to further insight about the dynamics involved in the discharge process. The existing laser system is costly and difficult to use in the field. We will show however that similar performance can be achieved with a solid state laser and frequency conversion by nonlinear optics. Such a compact system can be tuned to cover the wavelength range from 240 nm to 350 nm.
Ablation effect on an impulse discharge induced by a laser-plasma channel
Michihiro Uchiumi, Kiyotaka Ueda, Katsunori Muraoka, et al.
In order to develop a technique to induce a negative impulse discharge by a laser-ionized channel in a rod-to-rod electrode configuration, the ablation effect on the induction has been examined. Single irradiation by a high- power CO2 laser on the surface of the copper high- voltage electrode produced a luminous plasma plume. This ablation plasma was used for a discharge induction by an ionization channel created by a XeCl laser. It was found that the ablation enhances the trigger and guide effect for induction of a long gap discharge. The guide length was elongated approximately twice. The ablation plasma bead reduced the 50 percent sparkover voltage and the sparkover time. Electrical discharge leaders were observed by a flaming image converter camera. The ablation plasma bead made an early start of the leader from the high-voltage electrode and accelerated the leader advancement.
Contraction of laser-generated plasma channels under ambient electric fields
Mikhail F. Borisov, Valentin M. Gromovenko, Vladimir A. Lapshin, et al.
To define more precisely the requirements to electric- physical parameters of laser-generated plasma channel needed to trigger a lightning, the analysis of the experimental data on laser-guided long gap discharges is used. The analysis is based on the developed theoretical model of the channel interaction with thunderstorm electrical fields. Two modes of leader progression form a tip of the channel are considered. The obtained data allows determining the principal conversion conditions of the channel into a leader channel. To maintain the plasma channel conductivity during the modes, two laser pulses is supposed to be used. The suggestion was tested experimentally by the use of CO2 and Nd laser.
Laser-Triggered Discharge and Laser Isotope Separation
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Laser-triggered spark discharges using ultrashort-pulse lasers
Bruno M. La Fontaine, D. Comtois, C. Y. Chien, et al.
This paper presents result form a systematic study of the feasibility of triggering lightning in a controlled fashion, using ultrashort pulse lasers. We show the importance of producing a plasma with local gradients of electron density by focusing the laser beam in order to trigger streamers, which are the first condition required for the initiation of large-scale spark discharges. We present evidence of the ability of laser filaments to guide streamer discharges, which are akin to the final jump phase of a lightning discharge. We also demonstrate that the leader propagation can be considerably modified by the presence of a laser- produced plasma channel, in a rod-plane electrode geometry. Finally, we have developed numerical models for the ultrashort pulse laser beam propagation through air, plasma production and streamer inception.
Current measurements in plasma produced by the train of 10.6-um subnanosecond laser pulses
Victor V. Apollonov, K. Kh. Kazakov, N. V. Pletnyev, et al.
Results of current probe measurements for a plasma produced by the train of approximately 200 ps 10.6 micrometers laser pulses are reported. The train of pulses was obtained as a result of regenerative amplification of approximately 100 ps laser pulse in a 5 cm aperture 6 atm TE-CO2 laser. Experiments were carried out for Wo and Al targets dispersed in vacuum, two values of the interpulses separation in the train (Delta) T equals 9.3 and 29 ns and wide range of energy density on the target, corresponding to peak intensities of single pulses Ip equals 1 divided by 300 GW/cm2. Experiments had shown large difference of temporal structure of current signal with Wo and Al targets due to the considerable different in melting temperatures of these materials as well as radiation loses of laser plasma. We detected large ratio of current signal amplitudes for targets irradiation by the pulse train or gain switched pulse generated in TE-CO2 laser without injection of a short pulse. Results of these measurements are compared with those earlier obtained for nanosecond pulse train.
Characteristics of a laser-triggered discharge by high-repetition-rate excimer laser on dc electric field
Michiteru Yamaura, Satoshi Ihara, Saburoh Satoh, et al.
We selected UV lasers which have the advantage of getting a long plasma channel in air and high repetition rate of laser operation. We investigated the fundamental characteristics of laser induced-discharge for different kinds of gases using a kHz order repetition rate UV lasers. Consequently, the 50 percent breakdown voltage in oxygen and dry air except in nitrogen decrease with the burst of frequency with a KrF laser beam. This phenomena seems to be due to the photodetachment of negative ions of oxygen. On the other hand, when nitrogen gas was used, the effect of photodetachment could not be confirmed. For the KrF laser beam irradiations, the 50 percent breakdown voltage was lowest in oxygen gas.
Magnetic field effect on laser isotope separation of gadolinium and zirconium
Hideaki Niki, Iwao Kitazima
In laser isotope separation based on polarization selection rules the effect of magnetic field on isotopic selectivity was investigated. Excitation dynamics of atoms by linearly polarized lasers were numerically analyzed for J equals 2 yields 2 yields 1 yields 0 stepwise excitation under a magnetic field. Time evolution of the population in each magnetic substrate was calculated by solving the rate equations under the condition in which the atomic alignment is gradually destroyed by precession motion of the angular momentum around a magnetic field. It was found that a relatively small magnetic field may cause a selectivity loss and the field strength component perpendicular to laser polarization direction should be kept as small as the terrestrial magnetic field to obtain a high selectivity in the case of gadolinium isotope separation.
Dynamics of hydrogen chloride elimination from halogenated ethane induced by infrared multiphoton absorption
Atsushi Yokoyama, Toshiyuki Takayanagi, Keiichi Yokoyama
Dynamics of hydrogen chloride elimination from halogenated hydrocarbon through thee-center and four-center transition states has been elucidated by the measurement of translational, rotational, and vibrational energy distributions and ab initio molecule orbital calculations. Difference of the dynamics has been discussed on the basis of the transition state structures and/or structural change along intrinsic reaction coordinate calculated by an ab initio molecule orbital theory.
Lasers for Energy Engineering
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High-power laser chains used for laser isotope separation
Louis Andre Lompre
Since 1985, France has chosen to focus on the selective photo-ionization process called SILVA for uranium enrichment. The general SILVA schedule has led to the construction of a pilot facility called ASTER, aimed to a general assessment of SILVA. It utilizes a mid power dye laser chain pumped by copper vapor laser chains. An alternative solution to pump dye laser is under development. It is based on high-power diode-pumped frequency doubled Nd:YAG modules. Performances as high as 150 Watts, at 532 nm, 10 kHz and pulse duration shorter than 75 ns have been obtained. The electrical efficiency overpasses 5 percent. The paper will give a description of the high power laser chains used or proposed for laser isotope separation.
Computer-aided physical design of large-bore copper-vapor laser
Deli Yu, Yongxiang Tao, Xianhua Yin, et al.
A kinetic model for a series of large-bore copper-vapor lasers is completed. It includes the electric differential circuit equations and the nonlinear partial kinetic equations, and the equations are resolved by the method of Runge-Kutta and implicit difference respectively. On the basis of consistent computational results the radius kinetic parameters are presented, they are stimulating electric field, the plasma electron temperature and output power under different charging voltage are presented. The space- time behavior of the laser intensity is also shown in this paper, then we can conclude that the buffer gas pressure takes an important role in the large bore copper vapor laser. There is very agreement that exists between the calculated and measured results for the diameter of 6.5-cm copper vapor laser. So we predict some results of the copper vapor laser of diameter of 8.0 cm.
Development of high-power dye laser chain
Chikara Konagai, Hironobu Kimura, Teruichiro Fukasawa, et al.
Copper vapor laser (CVL) pumped dye laser (DL) system, both in a master oscillator power amplifier (MOPA) configuration, has been developed for Atomic Vapor Isotope Separation program in Japan. Dye laser output power of about 500 W has been proved in long-term operations over 200 hours. High power fiber optic delivery system is utilized in order to efficiently transport kilowatt level CVL beams to the DL MOPA. Single model CVL pumped DL oscillator has been developed and worked for 200 hours within +/- 0.1 pm wavelength stability. Phase modulator for spreading spectrum to the linewidth of hyperfine structure has been developed and demonstrated.
X-Ray Lasers
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X-ray lasers: an intense radiation source usable in the laboratory
Collisional soft x-ray lasers are brighter by several orders of magnitude than any other available source in the wavelength range comprised between a few tens and a few nanometers. Then, a new line of research has recently appeared besides continuing works aimed to improve optical properties of x-ray lasers and to develop new types of x-ray lasers. It consists in using the actual x-ray lasers as an efficient tool to produce and to study other phenomena in various fields such as atomic physics, plasma physics, or surface science. This paper gives a survey of recent x-ray laser progress and some examples of x-ray laser applications experiments.
Plasma diagnostics with a tabletop soft x-ray laser
Jorge J. G. Rocca, Mario C. Marconi, Jorge Filevich Chamatropulos, et al.
We discuss the first demonstrations of plasma diagnostics using a tabletop soft x-ray laser. A very compact capillary discharge pumped Ne-like Ar laser operating 46.9 nm was used to perform shadowgraphy and interferometry experiments in discharge-created discharge plasma waveguide. In a second set of experiments we took advantage of the good spatial coherence of the capillary discharge laser to perform soft x-ray interferometry measurements. In a first experiment the laser was used in combination with a simple wavefront division interferometer based on Lloyd's mirror to map the electron density distribution in the cathode region of a pinch discharge. In our most recent experiment we used an amplitude division interferometer, which utilizes diffraction grating as beam splitters, to probe a large scale laser-created plasma. Both interferometer schemes can be adapted to operate at the wavelength corresponding to any of the presently available saturated soft x-ray lasers.
Development of tabletop transient collisional excitation x-ray lasers
Masataka Kado, Tetsuya Kawachi, Noboru Hasegawa, et al.
An ultra-short pulse CPA laser system for x-ray laser driver has been developed with a combination of Ti:sapphire front end and Nd:glass rod amplifiers. This laser system has two beam outputs and each beam line produces 20J pre pulse and 20J main. This laser system is designed for x-ray laser pumping driver, especially for transient gain scheme. The new transient gain x-ray laser scheme with thin foil metal targets has been proposed. This scheme has higher laser energy efficiency and less x-ray laser refraction effect and makes possible to generate shorter x-ray wavelength with a compact table-top sized laser system. The electron temperatures of plasma heated with a short pre pulse and short main pulse have been calculated with 1D hydrodynamic code and obtained electron temperature higher than 1 keV with 20J laser energy. X-ray laser propagation is also calculated with gain guiding effect.
Uniform line focus and multitarget coupling for the creation of near-water-window nickel-like x-ray laser
Huajing Tang, Hiroyuki Daido, Stephane Sebban, et al.
To obtain high gain saturated amplification soft x-ray lasing output, uniform and long amplification medium must be created by focusing and target set-up technology. We report on the cylindrical lens array and multi target coupling system for creating uniform line focus. Through these methods, serial x-ray lasing with the wavelength towards the wavelength of water window are obtained on the GekkoXII Nd glass laser facility in ILE, Osaka, University.
X-Ray Lasers and Laser-Plasma X-Ray Sources
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Commercial terawatt femtosecond laser-driven tabletop x-ray lasers in gases
Peixiang Lu, Hidetoshi Nakano, Tadashi Nishikawa, et al.
Table-top x-ray lasers driven by a commercial terawatt (TW) femtosecond laser in gases such as N2, O2, SF6, and Kr are investigated. X-ray lasing to the ground state in low-charged nitrogen and oxygen ions is successfully demonstrated using a commercial TW femtosecond laser system by optical-field ionization. Small signal gain coefficients of 9.6 cm-1 for the NIII 3s(2S)-2p)2P) transition at 45.2 nm and 11.7 cm-1 for the OIII 2p3s(3P)-2p2(3P) transition at 37.4 nm x-ray lasers are achieved for a linearly-polarized 100-fs pump laser pulse of 25 mJ. Four models that includes the monopole collisional excitation and radiation trapping effects in neon-like S and nickel-like Kr ions were built and gains for neon-like S 3p-3s and nickel-like Kr 4d-4p transitions were calculated in SF6 and Kr gases with different gas pressures. Calculations yield positive prospects for table- top neon-like S and nickel-like Kr ion x-ray lasers driven by a 1-TW circularly-polarized 100-fs laser pulse.
Laser-plasma x-ray source by cryogenic target and high-repetition-rate slab YAG laser
Takayasu Mochizuki
X-ray generation using Ar, Kr and Xe cryogenic targets is investigated and compared. Strong x-ray emission at (lambda) equals 3.2 nm from Ar, (lambda) equals 9.0 and 10.0 nm from Kr and (lambda) equals 10.8 nm from Xe are observed. The x-ray conversion efficiencies of Ar, Kr and Xe cryogenic targets were 0.4 percent/sr/10 percent bw at IL equals 1 X 1012W/cm2, respectively, and were proportional to about 0.16, 0.07 and 0.3 power to the laser intensity, respectively. From gas cell target experiments, it is found that the initial target density is required to exceed 1021 cm-3. In cryogenic mixture targets the x- ray conversion efficiency per Xe mole fraction is found to have maximum values at a specific value of Xe fraction. Finally a high average power x-ray generation is demonstrated using a device of continuous supply of the target and a high average power high rep rate Q-switched YAG slab laser driver that we developed.
X-ray emissions from clusters excited by ultrashort laser pulses
Eisuke Miura, Hiroshi Honda, Keisuke Katsura, et al.
Properties of x-ray emission from rare gas clusters excited by ultrashort laser pulses were investigated. M-shell emissions from Xe clusters excited by Ti:sapphire and KrF laser pulses were compared under the same irradiation conditions. For the KrF laser irradiation, the absolute x- ray yield in the wavelength region from 0.8 nm to 1.6 nm was estimated to be 3 (mu) J/se per pulse, which was 20 times higher than that for the Ti:sapphire laser irradiation. Absolute x-ray yields in the wavelength region from 2 nm to 20 nm were measured for various rare gas clusters excited by a KrF laser pulse. For Xe, and x-ray conversion efficiency in the wavelength region from 5 nm to 20 nm was measured to be 1.1 percent sr, which was comparable to that for irradiating solid targets. The high x-ray conversion efficiency for Xe was brought about by the high absorption fraction of the laser light in the gas jet containing clusters.
Laser-Plasma X Rays and Laser Applications
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Hot electrons in femtosecond laser-plasma interaction
Jie Zhang, Tianjiao Liang, Yutong Li, et al.
The behaviors of hot electrons in femtosecond laser-plasma interaction have been studied systematically under laser irradiance of 5 X 1015 Wcm-2micrometers 2. A very directional jet emission of hot electrons with energies above 170 keV has been observed in the normal direction to the target surface. The angular distribution of the jet emission of hot electrons has been found to be dependent on the energy of hot electrons. By measuring the Faraday rotation angle of the backscattered emission, a magnetic field in the axial direction has been detected for the first time. The maximum value of the magnetic field was estimated to be as high as 1.76 +/- 0.7 Mgauss at such a modest irradiance. It is believed that this axial magnetic field is generated by the dynamo effect in the laser-plasma interaction.
Diagnostics and applications of laser-produced plasmas
Eckhart Foerster, Randolf Butzbach, Paul Gibbon, et al.
X-ray spectroscopy is one of the most important diagnostics of laser-produced plasmas, finding application in diverse areas such as laser fusion, x-ray lasers, and novel experiments using shot-pulse lasers to probe chemical and biological phenomena on the femtosecond timescale. Depending on the aims of these experiments, either high resolution spectra combined with either spatial or time resolution, or monochromatic x-ray spectrometer was also used here in x-ray diagnostics of 4f yields 3d transitions in Nickel-like transitions of elements with atomic numbers between 70 and 74. The dependence of this x-ray emission on laser energy, spot size, and target materials provides information about ionization degree, electron temperature and density - important parameters for the population inversion of a Ni- like x-ray laser in the water window.
Laser-excited gamma source with high spectral brightness
Alexander A. Andreev, Yuri V. Rozhdestvenskii, Konstantin Y. Platonov
This paper considers various channels of (gamma) -quantum generation via an ultra-short high-power laser pulse interaction with different targets. We analyze the possibilities to create a pulsed (gamma) -radiation source using laser triggering of some nuclear reactions and isomer targets. It is shown that 0.2 MeV monochromatic short pulse of (gamma) -radiation can be obtained with pulse energy sub- mJ level from isomer atoms localized in a magnetic trap. For nuclear reaction channel in light-atom materials, it is shown that 100-TW laser pulse gives rise to formation of about 106 (gamma) -photons near 5 MeV energy.
Poster Session I
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Scaling up of nonchain HF(DF) laser initiated by self-sustained volume discharge
Victor V. Apollonov, Konstantin N. Firsov, Sergey Yu. Kazantsev, et al.
Scaling problems are considered for non-chain HF laser operating on mixtures of SF6 and hydrocarbons in which a chemical reaction is initiated by self-sustained volume discharge. The possibility of obtaining a volume discharge in SF6 and in corresponding mixtures without preionization, i.e., self- initiated volume discharge (SIVD) is a new qualitative result in solving the scaling problem for non-chain lasers. The dynamics of SIVD evolution has been investigated. The possibility of obtaining SIVD is determined in SF6 by mechanisms that limit the density of current, are related to specific energy release, and prevent the total energy from flowing through a single channel. A simple mode is developed for calculating the discharge characteristics in non-chain laser. The model provides a good agreement with experiment data. The obtained energy of nonchain HF-laser is 407 J and that of DF-laser is 325 J with the electric efficiency 4.3 percent and 3.4 percent, respectively. A possibility is estimated of creating non-chain HF lasers with the output energy of the order of kilojoules and higher on the basis of experimental data obtained.
Development of efficient forward Raman pulse compression system for e-beam-excited KrF laser ASHURA
Yuji Matsumoto, Eiichi Takahashi, Isao Matsushima, et al.
We have developed a simple method of power multiplication. In this method, multi-path forward Raman amplifier is used. By multi-path amplification, it is possible to transfer almost all energy from long duration pump pulse to short Stokes pulse with small numbers of beams. The demonstration experiments of this method have been carried out by using a short pulse Stokes generator, a forward Raman Preamplifier and a forward Raman pulse compressor. Pump light is one of the sequential output pulses from the e-beam excited KrF laser system ASHURA. Short STokes pulse is generated in the Stokes generator filled with a mixture of methane and hydrogen gases as Raman scattering medium. The Stokes pulse is amplified to almost half of pump intensity by the Raman preamplifier also filled with same kinds of mixed scattering medium. The Raman pulse compressor is a 5-path amplifier with total Raman gain of 10. In latest experiments, the output Stokes pulse grew up to 3.2 times pump intensity by Raman conversion of pump power of 70 percent. The waveform of output Stokes was similar shot pulse as initial Stokes light.
Electron-beam-pumped high-repetition-rate KrF laser system
Eiichi Takahashi, Isao Okuda, Yuji Matsumoto, et al.
A repetition-rate electron beam pumped KrF laser amplifier is being built at the Electrotechnical Laboratory to develop the technologies required for an inertial confinement fusion energy driver. The pulsed power system of the prototype amplifier has already been competed and generates pulses of -300kV, 80ns with a repetition-rate of 1Hz. The high voltage electric short pulses are obtained by step-up pulse transformers, magnetic switches and a water dielectric pulse forming line instead of a conventional Marx generator with gap switches. One of the key technologies with this system is the cooling method of pressure and anode foils in a HIBACHI structure to increase those lifetimes. Our design adopts radiation and conduction as the main cooling processes and allows the foils to reach a high temperature. HAVAR and molybdenum are chosen as pressure and anode foil respectively instead of conventional titanium foils. The maximum temperature of the foils were numerically estimated to show the feasibility of the design.
High-average-power laser medium based on silica glass
Yasushi Fujimoto, Masahiro Nakatsuka
Silica glass is one of the most attractive materials for a high-average-power laser. We have developed a new laser material base don silica glass with zeolite method which is effective for uniform dispersion of rare earth ions in silica glass. High quality medium, which is bubbleless and quite low refractive index distortion, must be required for realization of laser action. As the main reason of bubbling is due to hydroxy species remained in the gelation same, we carefully choose colloidal silica particles, pH value of hydrochloric acid for hydrolysis of tetraethylorthosilicate on sol-gel process, and temperature and atmosphere control during sintering process, and then we get a bubble less transparent rare earth doped silica glass. The refractive index distortion of the sample also discussed.
High-power regenerative amplifier
Goichi Ohmae, Takashi Yagi
We have been investigating the possibility of ultimate down sizing of the CPA system by improving over all efficiency to convert the green pump energy to the Ti:sapphire wavelength by optimizing the regenerative amplifier. A regenerative amplifier with high gain to achieve small signal and saturated amplification was constructed. By selecting cavity parameters which allow for large gain cross section in the regenerative amplifier we obtained a pulse energy of 13mJ amplified form sub-nanojoule of the seed pulse in 11 round trips. We achieved overall efficiency of 15 percent in single amplifier pumped by single green source.
Multiwedge array for uniform target irradiation
Masaru Iwasaki, Takahisa Jitsuno, Noriaki Nishi, et al.
The effectiveness of multi-wedge plates array for the improvement of the laser irradiation uniformity on the pellet target in inertial confinement fusion has been investigated. A multi-wedge plates array of 90-mm in diameter was fabricated with wedge plates of 7 pairs, which ad a size of 30-mm diameter and a wedge angle of about 0.1 degrees. Also, to prevent the diffraction caused by each wedge plates, a soft aperture with the transmission profile of 16th super gaussian was designed and fabricated. As the result, it was confirmed that the array decreased the low- mode uniformity and is able to control the beam profile.
Magnetically suspended pellet for laser fusion scheme as a basis of fueling
Aki Shimamura, Akihisa Sato, Hiroki Yoshida, et al.
In our laboratory, Magnetically Suspended Pellet (MSP), which is a Ni-coated Glass Micro Balloon (Ni-GMB) suspended in non-contact fashion in a vacuum chamber, has been studied. Three items are described in this paper. The first section presents the development of Magnetically Suspension System (MSS). The second is given about the method of horizontal damping of MSP using optical forces or electrical force. Optical forces are assumed to be the radiometric force and the photon force. The photon force is larger than the radiometric one at pressure below 28mPa. We want to develop another method using electric force. We can ascertain that the MSP is charged and moved in the electric field.In the third section, we propose novel methods to measure the specific susceptibility of a Ni-GMB and the thickness of a Ni thin film. The specific susceptibility of Ni-GMB Km is measured by observing the trajectory of Ni- GMB immersed in an oil bath. It is found that the Km is 9.75 at room temperature. The other method has been developed for the measurement of thickness of a Ni thin film. The method is that a base plane is made on the Ni thin film by pulsed laser ablation first, and next the thickness is measured referred to this base plane by multiple beam interferometry. Our proposed method can effectively give the thickness corresponding to that obtained from the quartz crystal monitor within measurement error with the inferred uniformity less than 5 percent.
Simulation study on ablation and evacuation of liquid metal in laser fusion reaction chamber
Masato Kabetani, Keiji Yamamoto, Hideo Nagatomo, et al.
Using the theories of photon count statistic and test data of the ultraweak photon emission from biological system, the biophoton field's spectra distribution properties were studied in this paper. An experimental setup for testing UPE in different spectral region were designed. The test data proved UPE of living biological system exists in wide spectra region from UV-visible to IR. Using the test data, we can obtain important conclusions that is UPE almost has nothing to do with wavelength. The conclusion has important significance for proving the bio-photon coherence. In the end of this paper, the medical applications of UPE in 21st century were discussed simply.
Analysis of exploding plasma behavior in various magnetic fields
Takanobu Muranaka, Hideki Nakashima, Hideyuki Uchimura, et al.
Plasma behaviors in various magnetic fields were discussed by using the result from a 3D hybrid code. First, an instability of expanding plasma in a uniform magnetic field was discussed by comparing experimental data with numerical result. The effect of magnetic field diffusion on the plasma instability was studied. Second, the plasma behaviors in a dipole field were examined and comparison was made among the experimental data, MHD analysis and the result from the 3D hybrid code. So far, an overall good agreement among these result was found.
Conditions for initiation of effective thermonuclear burning of laser targets
Aleksey A. Levkovskii, Alexander A. Andreev, Dmitrij V. Il'in, et al.
The results of Monte-Carlo modeling of volume and spark ignition of spherical laser targets are systematized and the critical parameters are obtained both of isobaric and of isochoric central ignitors. It is shown that the target thermonuclear (TN) burning is independent on ignitor present if the ignitor dimension and temperature lower than the critical ones. In the opposite case TN flash result in effective burning with gain G-100, and the TN energy release is practically independent on the further increase of ignitor parameters. The intermediate gains 1 < G < 100 are obtained in rather narrow range of ignitor parameters near the critical. It is shown that the values of critical ignitor parameters are very sensitive to the way of ignition. The critical dimensions of isobaric ignitors are greater by several fold than ones of isochoric ignitors. On the contrary the overcritical target gain is practically independent on ignition origin and may be evaluated with a good accuracy by the simple asymptotic expression. The isochoric spark ignition associated with the fast ignition scheme is considered in detail and evaluations of minimum energy absorbed by extra laser pulse in terms of energy absorbed by basic driver are presented.
Observation of low-mode implosion nonuniformity of plastic-shell targets in the acceleration phase
Manabu Heya, Hiroyuki Shiraga, Masaharu Nishikino, et al.
IN order to directly observe low-mode implosion nonuniformities, especially of l equals 1, which prevents stable formation of a hot spark in the compressed core plasma at the final stage of the implosion, a series of direct-drive implosion experiments has been performed at the Gekko-XII glass laser facility by using gas-filled plastic- shell targets. Partially coherent light (PCL) was used as a drive laser to suppress middle- to higher-modes of the irradiation nonuniformity down to approximately 1 percent. A clear shift from the center of the chamber and a slight crosswise structure were seen in the time- and space- resolved shape of the shell in the accelerating phase with an x-ray framing camera and absorbed laser intensity were also estimated by using a rocket equation. In order to confirm the property of these results, separate experiments under similar laser conditions were performed by using Au- coated sapphire spheres as surrogate target. The x-ray intensity distribution on the circumference of the target in the XFCs image, which is strongly dependent on the drive nonuniformity in the accelerating shell resulted from the l equals 1 drive nonuniformity. In our experiments, the l equals 1 drive nonuniformity due to some reproducible factors was found to be of the order of approximately 10-20 percent.
Indirect/direct hybrid drive implosion experiments with x-ray pre-irradiation
Masaharu Nishikino, Hiroyuki Shiraga, Noriaki Miyanaga, et al.
Indirect/direct-hybrid drive scheme to suppress the initial imprint of the laser irradiation nonuniformities has been proposed and investigated as a new drive scheme for inertial fusion. In direct drive inertial confinement fusion, initial imprinting of laser irradiation nonuniformity is considered to cause seeding of the perturbation on target surface in the very beginning of the irradiation which may be amplified by Rayleigh-Taylor instability in the acceleration phase of the implosion and be deleterious to efficient heating of the hot spark at the center of the compressed fuel core plasma. In indirect/direct-hybrid drive scheme, the target is first irradiated very uniformly with low-intensity soft x-ray prepulse from external sources apart from the target. Indirect x-ray pre-irradiation of the surface causes a pre- expansion layer of the plasma before the irradiation of the direct drive laser beam. When the drive beam comes later, the target has a substantial stand-off distance between the ablation front and the beam absorption region. Thus the thermal smoothing effect is expected to occur in this transport layer, and the initial imprint can be significantly reduced. We have demonstrated planar target experiments on the indirect/direct hybrid scheme and observed reduction of the initial imprint. Implosion experiments the indirect/direct hybrid drive spherical capsules with external x-ray sources has been started. Overall implosion was performed successfully.
Computational study of x-ray radiation effects on hydrodynamic instability
Naofumi Ohnishi, Hideo Nagatomo, Hideaki Takabe, et al.
The initial imprint of density perturbation due to spatial nonuniformity of laser intensity is one of the most important issues in laser fusion research. Several imprint mitigation scheme by means of soft x-ray radiation have been proposed to reduce the induced perturbation through the thermal conduction region. One of the schemes uses an external x-ray source prior to laser incidence to produce preformed plasma. Another has a low-density foam layer and high-Z material to heat the foam radiatively and make it uniform. We present the dynamics of these schemes and the perturbation growth with nonuniform laser from the results of 2D simulation using our integrated code.
X-ray spectroscopic analysis of the influence of low-modal nonuniformity on the formation of a hot spark
Yoshihiro Ochi, Mitsuhiro Fukao, J. Sunahara, et al.
In the direct-drive scheme implosion of the inertial confinement fusion, the hot spark formation is critically affected by laser irradiation non-uniformities and subsequent hydrodynamic instabilities. Influence of the low- modal irradiation non-uniformities on the hot spark formation was investigated by means of the time- and space- resolved x-ray spectroscopic measurements. Experimental results were compared with post-processed hydro-code simulations by the aid of x-ray spectrum analysis code.
Hydrodynamic model experiment of the collision of supernova 1987A with its circumstellar ring using high-power laser
Young-Gwang Kang, Hiroaki Nishimura, Hideaki Takabe, et al.
Laboratory simulation of the ejecta-ring collision of Supernova 1987A has been performed by using a high power laser syste. Pure hydrodynamic modeling was applied using the invariance of the Euler equations and the experiment was designed with 1D hydrodynamic simulations. Three laser beams of (lambda) equals 0.53 micrometers , at the intensity I equals 2 X 1014 W/cm2 irradiated a CH foil to generate a strong shock wave and subsequent dense plasma flow in a low density CHO foam including a solid sphere at its center. Shock wave propagation and ma sam flow with vortex ring-like structures were observed with gated x-ray radiography. Overall hydrodynamic behaviors are consistent with 1D and 2D hydrodynamic simulations. The collision dynamics is dominated by a complicated interplay of reflected shock, diffracted shock, transmitted shock waves, and plasma flow behind the main shock passage.
Laser plasma on the late stages of its expansion
Serguei Silnov
The aim of the experiments was to study the characteristics of atoms, ions, electrons, and molecular compounds obtained in plasma bunch produced by laser's pulse - very complicated object with active processes of interaction of particles, emission and absorption of the radiation. The main problem of the investigation was to construct, by using the dates obtained far from plasma bunch, the atoms, That model is main instrument for study of influence these processes in forming of the ions' parameters on the earliest stage of producing and expansion of laser plasma. The knowledge of the behavior of laser plasma mae possible to control the parameters of the atoms, ions and electrons of plasmas and obtain the beams of multi-charge ions with desirable characters for some experiments in nuclear physics.
High-harmonic generation in an intense femtosecond laser field
ChangHee Nam, H. J. Shin, DongGun Lee, et al.
Generation of high harmonics in a femtosecond laser field with intensity far exceeding the saturation intensity for optical field ionization is investigated. As the laser intensity was increased, the time of strong high harmonic generation became earlier. As an atom is exposed to a larger electric field variation duration the harmonic emission, the emitted harmonics experience a blueshift due to a non- adiabatic effect. In addition the high harmonic spectra shoed very complex structure, which was analyzed using a semi-classical theory based on the strong field approximation.
Ultra-intense laser propagation with measurement of backscattered light image and spectrum
Takeshi Miyakoshi, Kazuo A. Tanaka, Ryosuke Kodama, et al.
We have newly developed a 2D space-resolved spectrometer for an ultra high intense laser plasma experiment. Output of this data, we can obtain 4D information: space, spectrum, and intensity. An optical fiber bundle is combined with a Cross Czerny-Turner type spectrometer to acquire 2D space- resolved spectrum. This has the spectral resolution 0.8 nm and the space 8 micrometers . Back-scattered light was measured from plasmas irradiated with a n ultra-intense laser pulse at laser intensity 1019 W/cm2. The obtained spectra show distinctive difference depending on both spatial and intensity profiles.
Fast ion generation in ultra-intense laser interactions with plasmas
Hideaki Habara, Ryosuke Kodama, Yasuhiko Sentoku, et al.
In order to study the ion acceleration in ultra-intense laser plasma interactions, we measured neutron spectra from the D-D ion nuclear reactions in the target. 50-100TW/0.5-1 ps laser light irradiated obliquely dueterated plastic solid targets with different laser polarizations and intensities. Comparing the neutron spectra with the 3D Monte-Carlo simulation indicates ion acceleration in the near target normal direction at any polarization and increases in the ion energy with laser intensity.
Dynamics of anisotropic Coulomb explosion of C60 under an intense laser field
Junkei Kou, Vasilii Zhakhovskii, Shuji Sakabe, et al.
C60 vapor was irradiated with an intense femtosecond laser pulse. Multiply charged carbon ions, up to C4+, were detected in the time-of-flight spectra. We have measured both energy and angular distributions with respect to the laser polarization direction for ions with different charge number. The kinetic energy of ions are distributed above 1 keV. The angular distribution measurement shows that the highly charged ions of C3+ and C4+ are mostly distributed in the direction parallel to the laser polarization, and the C+ ions are slightly distributed in the direction perpendicular to it. These observations clearly indicate that an anisotropic explosion takes place. The average energy of ions with the different charge number is found to be proportional to the square of the charge number, while the maximum energy is proportional to the charge number. Classical molecular dynamics simulations have been successfully carried out reproducing not only the energy spectra but also the angular distributions of ions. The simulations suggest that the most crucial process for the anisotropic Coulomb explosion of C60 is not the electron impact ionization, but the cascade hopping of electrons.
Proton acceleration by an intense laser supplemented with a static magnetic field
Hiroaki Ito, M. Bakhtiari, Masashi Imai, et al.
A new photon accelerator utilizing the laser wakefield acceleration scheme and the vp X B mechanism is proposed. In the proton acceleration employing the vp X B mechanism, we have performed the simulation with the Runge Kutta method. The result show that the protons are accelerated by the laser field, when the proton beam is obliquely incident on the propagation axis of the laser traveling with the speed of light. The energy gain per one stage is not large enough but the acceleration gradient is several hundred times larger than the conventional proton acceleration scheme. In addition, we expect that the acceleration method by a radial wakefield excited by an intense laser has more advantage than the vp X B mechanism in lower injection energy. It will be possible to make the compact proton accelerator with these principles.
Electron-beam instability in the slab-symmetric dielectric structure and stabilization assisted by pre-ionized plasma
Naotoshi Kirihara, Toshimitsu Nishino, Yasushi Nishida, et al.
The Vp X B acceleration scheme with use of a transverse electromagnetic wave is demonstrated experimentally. However, in order to couple particles with the transverse wave, a slow-wave structure has to be employed because of low electron beam velocity. When the electron beam propagated through the slow-wave structure composed of dielectric-loaded slab-symmetric waveguide in the present paper, an orbit of the beam because unstable. We have observed the electron beam instability to investigate its mechanisms. As a result, an electron beam in the dielectric-loaded waveguide is deflected to the opposite direction from the material on the waveguide wall. By adding the beam-generated plasma in the slow-wave structure the electron beam has been observe dot become stable.
Poster Session II
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Development of high-power copper vapor laser system
Hironobu Kimura, Nobutada Aoki, Noriyasu Kobayashi, et al.
A high power copper vapor laser (CVL) system in master oscillator power amplifier configuration has been developed for laser isotope separation program in Japan. Maximum output power of 650 W has been successfully achieved with 9- cm diameter and 350 cm discharge length amplifier. Also MOPA output power of 2.4 kW has been demonstrated in small master oscillator with 4 cm bore and 4 stage power amplifier with 9 cm bore configuration. The authors developed a thermal calculation code to maintain an optimum copper vapor density throughout a large volume and a new thermal insulation structure design method has been proposed to combine two different heat insulators to make longitudinal temperature distribution of the laser tube as flat as possible. A CVL discharge circuit has been improved by applying an excellent magnetic switch which prove a approximately 90 kV-4000 A pulse to a CVL at 4.4 kHz repetition rate. This paper reports such CVL design methods together with the performance of the designed high power CVL system.
Possible high-power high-beam-quality solid state laser operating in the x-ray band
Solid state lasers operating in the x-ray region are very attractive because of the potential high-energy developable. We present a possible solution to obtain high-energy pulses with suitable time duration from deformed crystals. DFB laser emission can be obtained in crystals using the anomalous transmission angle. Ohtsuki firstly proposed this solution. We discuss an alternative ring configuration and different methods of excitation from ultra short laser pulses to laser beams generated by cooled atom traps.
Characteristics of high-order harmonic generation from solid-surface plasmas depending on driving laser conditions
Atsushi Ishizawa, Teruto Kanai, Tsuneyuki Ozaki, et al.
Investigations have been performed on the spatial distributions of high-order generation from solid surface plasmas. It is found that the divergence of the harmonics gradually increases at intensities between I(lambda) 2 equals 2 X 1015 and 2 X 1016 X cm-2 X micrometers 2 ps, 1054 nm laser pulse with typical maximum intensities of approximately 2 X 1017 W X cm-2. We experimentally observe that the divergence of the harmonics decreases as the order of the harmonic increases. We also measured that the divergence of the third harmonic emission is smaller for 2.2 ps width lasers as compared with those for 100 ps pulse width lasers.
Harmonic generation by intense ultrashort laser pulses in rare gases
Nguyen Hong Shon, Akira Suda, Katsumi Midorikawa
The interaction of intense ultrashort laser pulses with a gas of argon atoms in numerically investigated. The investigation utilizes a model that solves both the time- dependent Schroedinger equation and the wave equation self- consistently. The time-dependent Schroedinger equation for a single-active electron in the effective static potential and in the potential of electron-laser interaction is solved using alternating direction implicit method. The Maxwell's wave equation is solved using an explicit finite-different technique. We show that, under some conditions, propagation effects significantly clean up the single-atom spectrum providing new spectrum with well-resolved harmonic structure.
High-gain broadband optical parametric chirped pulse amplification
S. K. Zhang, Masayuki Fujita, Hidetsugu Yoshida, et al.
Optical parametric chirped pulse amplification has apparent advantages over the current schemes for high energy ultrashort pulse amplification. High gain in a single pas amplification, small B-integral, low heat deposition, high contrast ratio and, especially the extremely broad gain bandwidth with large-size crystals available bring people new hope for over multi-PW level at which the existing Nd:glass systems suffered difficulties. In this paper we present simulation and experimental studies for a high gain optical parametric chirped pulse amplification system which may be used as a preamplifier to replace the current complicated regenerative system or multi-pas Ti:sapphire amplifiers. Investigations on the amplification pump and chirped broadband pulse as a seed, respectively. Analysis and discussions are also given.
X-ray emission from solid plasmas generated by femtosecond high-intensity laser pulses
Sudeep Banerjee, Riju C. Issac, P. P. Rajeev, et al.
We report observations of intense x-ray emission from solid targets excited by Ti:sapphire laser pulse of 1-fs duration and intensities up to 1016 W cm-2. We measured characteristic and continuum emission. X-ray emission and plasmas temperature were studied for s, p, and circular polarization states of the input laser beam. We find that circularly polarized light generates the least electron temperature compared to s and p polarizations. To complement these observations, single beam reflection from laser produced plasmas as measured. P-polarized light is reflected least, followed by circular and s-polarized light in that order. We believe that the circularly polarized light coupled into channels other than the heating of electrons even though it is absorbed more than the s-polarized case. We have also carried out x-ray emission studies with longer input pulses and find that the spectrum is mostly line emission with hardly any continuum.
Monochromatic x-ray radiation from a vacuum diode with a laser-irradiated cathode
Andrei S. Shikanov, Alexei A. Erokhin, Yuri V. Korobkin, et al.
Investigation of spectral, spatial and temporal characteristics of a monochromatic point x-ray source of photon energy approximately 5 keV has been carried out. The source was set up using a laser produced titanium or aluminum plasma as a cathode and a point-tip titanium anode. Parameters of x-ray radiation in Ti K-shells are 1) spectral brightness of approximately 1021 photons/cm2.sec.sr.keV, 2) spatial size approximately 250 microns, and 3) x-ray pulse duration less than 20 ns.
Laser-plasma x-ray source using gas-target mixed fine particle
Tetsuya Matsui, Nobuyoshi Kogawa
We are developing laser plasma x-ray source for the extreme UV lithography. Our main idea is than fine particles, which sizes ar much smaller than the laser focal spot size, are used for the target of LPS. It is possible that this method has the higher x-ray conversion efficiency and low debris effect. Before the verification of this idea, the characteristics of LPS using the only gas puff target were investigated and tried the 100 Hz gas puff continuous operation until 106 shots. In this operation, the long- term stability of the x-ray signal from 105 shots to 106 shots was about +/- 8 percent. In order to confirm our idea, we have selected SnO2 fine particle that had a strong peak at 13.8 nm. It has found that the target of the gas mixed SnO2 fine particle had two times higher x-ray intensity than the only Xe gas target at 13.6-14.0 nm. Therefore, it seems suitable for the Mo/Si multi-layer mirror system.
Characterization of laser-produced gas-puff plasmas for soft x-ray projection lithography
Masayuki Suzuki, Hiroyuki Daido, Il Woo Choi, et al.
We characterize a laser produced gas puff plasma for soft x- ray generation. Strong emissions at 11.4 nm wavelength region was observed, using krypton and xenon gas puff targets irradiated by a 0.7J/8ns Nd:YAG laser. Space resolved x-ray spectra measurement indicated that the source size depends on the Rayleigh length and the gas density profile. A channeling effect for larger tare size which is connected with the thermal focusing has been observed.
Preplasma conditions for longitudinally pumped TCE soft x-ray lasers
Tsuneyuki Ozaki, Keiichi Yamamoto, Hiroto Kuroda, et al.
The conditions necessary for large gain-length products in longitudinally-pumped Ni-like Mo x-ray lasers are clarified using a 1D hydrodynamics code. Ray tracing shows that for effective amplification within the high density ultra-high gain region, waveguides such as capillaries must be used. The effect of inhomogeneous pumping of the capillary on gain is also evaluated.
Inner-shell ionization and hollow-atom x-ray lasers driven by high-intensity laser
Kengo Moribayashi, Akira Sasaki, Yutaka Ueshima
Inner-shell ionization and hollow atom x-ray lasers are studied in order to propose a short wavelength x-ray laser system. For hollow atom x-ray laser Mg vapor with 1017 cm-3 density and Larmor x-rays are treated as a target material and x-rays are treated as a target material and x-ray source, respectively. The Larmor x-rays are suitable as a pump x-ray source because they have high brightness and short pulse. Their peak intensity and energy spectrum are appropriate for inner-shell ionization. The necessary intensities of x-ray source are obtained by x-ray intensity of 1013W/cm2 and 3 X 1013 W/cm2 in inner-shell ionization and hollow atom x-ray lasers, respectively. For short wavelength inner-shell ionization x- ray emission, Na-like ions are good target. By x-ray intensity of 2 X 1015W/cm2 at a few keV photon energy, the gain is about 10 cm-1 for more than 10 fs with use of Na-like S ion.
Numerical analysis of high-gain transient collisional x-ray lasers
Akira Sasaki, Alexei G. Zhidkov, Takayuki Utsumi, et al.
We have developed a collisional radiative model of electron collisional excited x-ray lasers. We calculate the ion abundance and soft x-ray gain for the 4d-4p transition of Ni-like multiple charged ion, in short pulse laser irradiated plasmas. We combine a detailed model using the atomic data calculated by HULLAC code and the averaged model based on the screened hydrogenic approximation. In order to choose a proper set of the levels to be included in the atomic model, investigation of the model dependence of the gain is carried out. The population in the fine structure levels in 3d94s and 3d94f configuration, autoionizing double excited configurations of Ni-like and Cu-like ions are found to cause approximately factor of 2 difference in the soft x-ray gain. The steady-state gain and its dependence on plasma density and temperature are investigated over elements from z equals 45 to 65. The time dependent calculation for a plasma condition corresponds to a thin Ag foil irradiated by tow short laser pulse shows the transient gain which is 40 times greater than the steady state gain.
Effective molecular targets for a laser plasma XUV radiation source
Gagik Ts. Nersisyan, Valeri O. Papanyan
Metal targets covered by micrometer layers of metal- phthalocyanines or fullerenes are studied here. An increase in XUV yield due to the optimized absorption of the laser field is reported. Effects of high-temperature plasma rapid expansion were observed. Moderate power nanosecond and picosecond neodymium lasers are used to produce an incident intensity of 1011 to 1013 W/cm2 on the targets. The plasma electron density was measured by fitting observed spectral profiles to the theoretical profiles. Collisional, Doppler, and Stark broadening mechanisms were considered in the calculations. Our measurement technique permits us to determine the electron density and temperature dependence on distances from the target surface from 1 mm up to approximately 5 mm. Electron temperature was measured by comparing intensities of spectral lines, belonging to the ions having a different degree of ionization. Preliminary experiments show that conversion efficiency for molecular coated targets is greater by a factor of approximately 1.5 than measured form bulk solid metal targets.
Lightning energy conversion using lasers
Nasrullah Khan, Norman Mariun
Potential energy sources are being investigated for the socioeconomic needs and increased power demand. Systems employing nuclear, thermal, hydro, solar, volcano, MHD, tidal and wind power generation techniques already exist. This work describes our attempt to utilize the off-planet lightning charge to store super electrolytic batteries or super capacitors. The electrostatic charge on clouds can be shifted to earth through a conducive air plasma channel created by appropriate high power Q-switched and mode-locked laser. The pulsed laser may create a conducting path consisting of ionized air particles from earth to some upper atmosphere. An antenna connected to anode of super cell or positive terminal of the super capacitor will accumulate and store this charge for future use. The anode of battery or positive terminal of capacitor may be connected to earth to complete the circuit. Due to extremely loud thundering and tropical weather severity a detailed work was done on lightning regarding its temporal and spatial profiles to develop a reasonable model to explore transient charging characteristics. Experimental work in respect of laser inducted plasma wire creation and charging capabilities of super storage batteries or super capacitors is optimized. Latest experimental results are reported.
Experiments of discharge guiding using strongly and weakly ionized plasma channels for laser-triggered lightning
Yoshinori Shimada, Shigeaki Uchida, Chiyoe Yamanaka, et al.
Generation of a long laser-plasma channel capable of triggering and guiding an electrical discharge is a crucial issue for laser-triggering protection system. We make a long plasma channel to increase the probability of triggered lightning by laser. To produce a long laser plasma channel, we propose da new technique called hybrid plasma channel method which combines weakly and strongly ionized plasma channels to maximize laser-energy efficiency of discharge guiding. We investigate the characteristics of the hybrid plasma channels to maximize laser-energy efficiency of discharge guiding. We investigate the characteristics of the hybrid plasma channel method through several laboratory experiments. The weakly ionized channel was generated by UV laser pulses in air. As the number density of electrons in weakly ionized channel is proportional to 1.1 power of laser intensity, nitrogen and oxygen molecules can not attributed to the source of ionized plasma. It is suggested that dissociation process of impurities in air whose density is 1011 - 1012 cm-3 plays an important role in plasma formation and leader triggering effect. The 50 percent flashover voltage using the hybrid plasma channel method is lower than that without the weakly ionized plasma channel. It was also found that higher repetition rate of the plasma generation on lowers the V50 furthermore.
Leader development in laser-induced discharge under nonuniform dc electric field
Satoru Nagasawa, Mengu Cho, Masayuki Hikita, et al.
Laboratory experiments are carried out to study the mechanism of laser-induced discharge under non-uniform DC electric field as a basic research for the laser-induced lightening. Flashover voltage is measured against the position of the laser plasma. The result indicate that the laser-induced discharge occurs as the leader is formed at the rod electrode and works as an extension of the electrode. Images of leader are taken by a streak camera. The velocity and direction of leader propagation are identified. The velocity of the leader propagation is of the order of 103-104 m/s. The discharge occurs within a time-scale longer by one order of magnitude than the time for the leader to travel the electrode gap. This time difference is explained as the time to heat the plasma channel by Joule heating to from the leader.
Model experiments of laser-triggered lightning using an intense CO2 laser pulse
Megumu Miki, Atsushi Wada, Takatoshi Shindo
Discharges have been guided by a strongly ionized plasma channel under DC voltages. The plasma channel was produced by a 45J-CO2 laser pulse and reduced the sparkover voltage of the discharges in 0.5 m air gaps. Gap configurations tested were a rod-rod gap and a rod-sphere gap. For comparison of discharge characteristics under the DC voltage and the impulse voltage, experiments of the laser-guided discharge under a lightning impulse voltage have also been conducted. From these results, it is clarified that the corona discharges prevent the plasma channel form triggering the discharge under the DC voltage.
High-resolution spectroscopy of uranium atom by laser-induced fluorescence method
Masaki Oba, Katsuaki Akaoka, Masabumi Miyabe, et al.
High resolution spectroscopy were applied to measure the isotope shifts and hyperfine structures of atomic uranium including 236U and 234U isotopes. The isotope shifts between 234U, 235U, 236U and 238U, and the hyperfine structure of 235U were obtained in the even levels lying around 2 eV and high lying odd levels around 4 eV. In the 4 eV levels measurement, the data were obtained by the Doppler free two photon absorption technique.
Efficient selective excitation in optically thick extensive media by adiabatic population transfer
V. G. Arkhipkin, D. V. Manushkin, V. P. Timofeev, et al.
In this work, the feature of spatio-temporal evolution of tow partially overlapped short pulses of counterintuitive sequence in a medium of three-level absorbing atoms in conditions of adiabatic transfer of population are investigated. The analytic solution is constructed. It is shown, that selective excitation of two-photon resonant state with a near-unity probability is conserved on the length of medium, which is considerably greater than the absorption length of a weak probe pulse in the absence of a coupling pulse at the adjacent transition.
Ripple growth of laser beam propagating in the multilevel photoionization system
Yasushi Takizawa, Ryota Murakami, Koji Nagasaka, et al.
Spatial near-resonant effects on laser beam propagation in a multilevel photoionization system have been studied by 2D simulation. It was found that the initial amplitude of nonuniformity grows up during the propagation, which degrades the photoionization rate of the target atom. The spatial effects become large for the longer incident laser pulse. A semi-analytical formula to analyze the growth of nonuniformity in the multilevel photoionization system was derived.
Multiphoton dissociation and isotope separation of boron by FEL
Masaki Hashida, Yasukazu Izawa, Yukinori Nagaya
Multiphoton dissociation BCl3 using free electron laser was demonstrated for the first time. It was found that the dissociant yield in the laser irradiation region where the laser intensity exceeds the dissociation threshold is nearly 1. The maximum selectivity was 1.45 which increased gradually be decreasing the laser frequency toward red side from the vibrational resonance of BCl3. In order to discuss the present result, the dissociation experiments for TEA CO2 laser were also performed.
High-brightness gamma ray and its application for nuclear transmutation
Kazuo Imasaki, A. Moon
In this article, a generation of high brightness (lambda) ray and its application to transmutation of nuclear waste is discussed. The recent development of laser and optical technology allows us to storage the photons in a cavity. The interaction of electron beam with the storage photon field makes an enhancement of generation of high brightness (lambda) ray. Such (lambda) ray with high efficiency of generation is expected to use interesting applications as nuclear transmutation which has been studied at ILT. The result shows this method promising. We performed a small scale experiment with the low energy electron beam and accumulated photon in a super cavity. This results shows this method promising. We performed a small scale experiment with the low energy electron beam and accumulated photon in a super cavity. This result corresponded quite well to the predicted one form cavity storage rate and electron beam energy.
Laser Fusion Review and Laser-Plasma Physics
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Superhigh-power laser systems and their application
Chiyoe Yamanaka
Super high power laser systems have been pursued for the nuclear fusion research in these 30 years. GEKKO XII glass laser, LEKKO VIII CO2 laser, diode pumped solid state laser and PW cpa Nd glass laser are developed at Osaka University. They have proved to be very effective to the laser fusion research and also to the various applications in the wide fields of science and technology.
Then and now
Arthur Kantrowitz
I treasure the analogy between aging and climbing a mountain. Ofcourse there are differences, mountain climbing is usually voluntary. As you climb a mountain you lose the ground detail but on a clear day broad views ofthe landscape are visible. The view from the mountain top is sometimes helpful to those working on the ground. I hope that the broad view ofthe technological landscape I present today will be ofsome use to those ofyou still lucky enough to be tilling that landscape. I will refer primarily to the I JS scene hut I believe that the technological landscape is as universal as human nature
Advanced diode-pumped solid state laseres (DPSSLs): near-term trends and future prospects
The features of modern, high-power semiconductor diode laser arrays as sources for pumping high power solid state lasers are reviewed. The status and prospects for high power, high- beam quality Nd:YAG and Yb:YAG DPSSLs are examined. Developing concepts for novel high power DPSSLs are also outlined.