Faculty Profiles - Nakai Mitsuo

Papers - Nakai Mitsuo

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Theoretical modeling of laser-produced plasmas for development of extreme UV radiation source for lithography Reviewed

Nishihara K, Nishikawa T, Sasaki A, Kawamura T, Sunahara A, Furukawa H, Murakami M, Nishimura H, Shimada Y, Nakai M, Fujioka S, Shigemori K, Uchida S, Fujima K, More R, Koike F, Kagawa T, Zhakhovskii V, Hashimoto K, Yamaura M, Matsui R, Hibino T, Okuno T, Tao Y, Sohnatzadeh F.L, Nagai K, Norimatsu T, Tanuma H, Miyanaga N, Izawa Y

Inertial Fusion Sciences and Applications 2003 1069 - 1073 2004

A design window of laser and plasma parameters required for an extreme ultraviolet (EUV) radiation source for practical application for the next generation of lithography has been introduced. We present a simple analytical model of conversion efficiency from laser energy to radiation energy with a wavelength of 13.5 nm with 2 % bandwidth, by considering power balance of laser produced high-z plasma. We also investigate dependence of the EUV emission from tin and tin-oxide plasmas on laser intensity and wavelength in spherical geometry using the GEKKO XII laser system. It is found that the conversion efficiency into a 2% bandwidth about 13.5 nm has a maximum of a few percent near the laser intensity 10 11 W/cm 2. The efficiency is about the same for 1.053 μm and 0.527 μm laser wavelengths. A scaling law of the conversion efficiency on the laser intensity obtained agrees fairly well with the experimental results. The model also explains many features of the spectrum observed in the experiments.

First observation of density profile in directly laser-driven polystyrene targets for ablative Rayleigh-Taylor instability research Reviewed

S Fujioka, H Shiraga, M Nishikino, K Shigemori, A Sunahara, M Nakai, H Azechi, K Nishihara, T Yamanaka

PHYSICS OF PLASMAS 10 ( 12 ) 4784 - 4789 2003.12

The temporal evolution of the density profile of a directly laser-driven polystyrene target was observed for the first time using an x-ray penumbral imaging technique coupled with side-on x-ray backlighting at the GEKKO XII [C. Yamanaka , IEEE J. Quantum Electron. QE-17, 1639 (1981)]-High Intensity Plasma Experimental Research laser facility (I-L=0.7x10(14) W/cm(2), lambda(L)=0.35 mum). This density measurement makes it possible to experimentally confirm all physical parameters [gamma(k),k,g,m,rho(a),L-m] appearing in the modified Takabe formula for the growth rate of the ablative Rayleigh-Taylor instability. The measured density profiles were well reproduced by a one-dimensional hydrodynamic simulation code. The density measurement contributes toward fully understanding the ablative Rayleigh-Taylor instability. (C) 2003 American Institute of Physics.

Equation-of-state measurements of polyimide at pressures up to 5.8 TPa using low-density foam with laser-driven shock waves Reviewed

K Takamatsu, N Ozaki, KA Tanaka, T Ono, K Nagai, M Nakai, T Watari, A Sunahara, M Nakano, T Kataoka, H Takenaka, M Yoshida, K Kondo, T Yamanaka

PHYSICAL REVIEW E 67 ( 5 ) 2003.5

The laser-driven equation-of-state (EOS) experiments for polyimide are presented. The experiments were performed with emission measurements from the rear sides of shocked targets at up to a laser intensity of 10(14) W/cm(2) or higher with 351 nm wavelength and 2.5 ns duration. Polyimide Hugoniot data were obtained up to 0.6 TPa with good accuracy. Applying low-density foam ablator to the EOS unknown material, we also obtained the data at a highest pressure of 5.8 TPa in the nonmetal materials. Those data were in agreement with the theoretical curves.

Side-on measurement of hydrodynamics of laser-driven plasmas with high space- and time-resolution x-ray imaging technique Reviewed

S Fujioka, H Shiraga, M Nishikino, Y Tamari, K Shigemori, M Nakai, H Azechi

REVIEW OF SCIENTIFIC INSTRUMENTS 74 ( 3 ) 2198 - 2201 2003.3

We developed and improved high space- and time-resolution x-ray imaging techniques (3-6 mum, 100-200 ps). These techniques were coupled with side-on x-ray backlighting for observing hydrodynamics of directly laser-driven polystyrene plasmas. As a high sensitive x-ray image detector, Imaging Plate was introduced to penumbral imaging technique [S. Fujioka et al, Rev. Sci. Instrum. 73, 2588 (2002)]. Noise in penumbral images was reduced by this improvement, and high quality density profiles of plasmas were obtained. A large-magnification slit camera, whose-slit width and magnification were 4 mum and 82.8, was coupled with an x-ray streak camera (XSC). Due to the advantage of the large-magnification, high spatial resolution of 5.8 mum was found even with an XSC, the photocathode of which usually has low spatial resolution. These techniques are useful in understanding of hydrodynamic instability in inertial confinement fusion. (C) 2003 American Institute of Physics.

Temporal evolution of temperature and density profiles of a laser compressed core (invited) Reviewed

Y Ochi, Golovkin, I, R Mancini, Uschmann, I, A Sunahara, H Nishimura, K Fujita, S Louis, M Nakai, H Shiraga, N Miyanaga, H Azechi, R Butzbach, E Forster, J Delettrez, J Koch, RW Lee, L Klein

REVIEW OF SCIENTIFIC INSTRUMENTS 74 ( 3 ) 1683 - 1687 2003.3

Temporal evolutions of the electron temperature and density profiles in the inertial confinement fusion core plasma were obtained through a combination of experimental technology to create a uniform core, diagnostics developments,,and a data analysis technique to obtain an optimal solution. In the experiment, time- and space-resolved x-ray spectroscopic measurements were carried out; an x-ray streak spectrograph and a monochromatic x-ray framing camera provided temporal evolution of x-ray spectrum and monochromatic emissivities, respectively. The spectrum and emissivity profile were iteratively fitted as a function of electron temperature, density, and space. Then, optimal solutions were successfully extracted with the help of Niched-Pareto genetic algorithm. Temporal behavior between those data is well corrected by comparing spatially and spectrally integrated intensities. The resultant profiles were compared with hydrocode simulations, showing that spatially averaged electron temperature and density evolutions are well replicated by the simulations, but their detail spatial profiles do not agree with them. (C) 2003 American Institute of Physics.

X-ray imaging diagnostics for laser-driven hydrodynamic instability experiments Reviewed

H Shiraga, H Azechi, M Nakai, K Shigemori, M Nishikino, T Sakaiya, S Fujioka, Y Tamari, T Yamanaka

REVIEW OF SCIENTIFIC INSTRUMENTS 74 ( 3 ) 2194 - 2197 2003.3

Rayleigh-Taylor (RT) instability is one of the most important physical issues in the inertial confinement fusion research. The reduction of its growth rate due to laser-driven ablation, which is described by the modified Takabe formula, is of great importance for-a precise understanding of the target physics. We have developed various diagnostic techniques for the measurement of the parameters appearing in the Takabe formula, such as the growth rate, the acceleration, the mass ablation rate, and the density structure including ablation density and density scalelength. Face-on and side-on x-ray backlighting were coupled with moire interferometry imaging, penumbral imaging, and Fresnel zoneplate imaging. All the physical parameters related to RT instability were measured experimentally, and compared with simulation results. (C) 2003 American Institute Of Physics.

Equation-of-state measurements of polyimide at pressures up to 5.8 TPa using low-density foam with laser-driven shock waves Reviewed

K. Takamatsu, N. Ozaki, K. A. Tanaka, T. Ono, K. Nagai, M. Nakai, T. Watari, A. Sunahara, M. Nakano, T. Kataoka, H. Takenaka, M. Yoshida, K. Kondo, T. Yamanaka

Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics 67 ( 5 ) 5 2003

The laser-driven equation-of-state (EOS) experiments for polyimide are presented. The experiments were performed with emission measurements from the rear sides of shocked targets at up to a laser intensity of [Formula presented] or higher with 351 nm wavelength and 2.5 ns duration. Polyimide Hugoniot data were obtained up to 0.6 TPa with good accuracy. Applying low-density foam ablator to the EOS unknown material, we also obtained the data at a highest pressure of 5.8 TPa in the nonmetal materials. Those data were in agreement with the theoretical curves. © 2003 The American Physical Society.

High-speed x-ray radiographic measurement of laser-driven hydrodynamic instability Reviewed

H Shiraga, H Azechi, M Nakai, K Shigemori, M Nishikino, T Sakaiya, S Fujioka, Y Tamari, T Yamanaka

25TH INTERNATIONAL CONGRESS ON HIGH-SPEED PHOTOGRAPHY AND PHOTONICS 4948 425 - 430 2003

Hydrodynamic instability in laser-irradiated targets have been investigated in detail by using ultra high-speed x-ray radiographic technique. Recently developed high-resolution x-ray imaging for laser-driven Rayleigh-Taylor (RT) instability experiments as well as data including RT growth rate, ablation density and plasma density profile are described. Results are of great importance for comprehensive understanding of the dispersion relation of the laser-driven RT instability. Especially, direct observation of the ablation density was first achieved with temporal and spatial resolutions of 100 ps and 3 mum, respectively. Imaging technique includes x-ray Moire imaging, x-ray penumbral imaging and Fresnel phase zone plate imaging coupled with x-ray streak cameras or x-ray CCD cameras. Experiments were performed by using Gekko-XII/HIPER laser system at the Institute of Laser Engineering, Osaka University.

Hydrodynamic instability experiments on the HIPER laser Reviewed

K Shigemori, H Azechi, S Fujioka, Y Kanai, N Miyanaga, A Murakami, T Muranaka, H Nagatomo, M Nakai, M Nishikino, K Nishihara, H Nishimura, T Sakaiya, H Shiraga, A Sunahara, H Takabe, T Takayama, Y Tamari, A Tanaka, T Yamanaka

PLASMA PHYSICS 669 269 - 272 2003

We present recent results on the hydrodynamic instability experiments on the HIPER (High Intensity Plasma Experimental Research) laser facility at Institute of Laser Engineering, Osaka University. We measured the Rayleigh-Taylor growth rate on the HIPER laser. Also measured were all parameters that determine the RT growth rate. We focused on the measurements of the ablation density of laser-irradiated targets, which had not been experimentally measured. The experimental results were compared with calculations with one dimensional simulation coupled with and without Fokker-Planck equation for electron heat transport.

Progress in understanding of laser-produced plasmas for EUV source Reviewed

N Miyanaga, K Fujima, S Fujioka, Y Fujimoto, H Fujita, H Furukawa, K Hashimoto, T Hibino, T Kagawa, T Kato, T Kawamura, F Koike, R Matsui, R More, M Murakami, K Nagai, M Nakai, M Nakatsuka, T Nishikawa, K Nishihara, H Nishimura, T Norimatsu, T Okuno, A Sasaki, K Shigemori, Y Shimada, FL Sohnatzadeh, A Sunahara, H Tanuma, Y Tao, K Tsubakimoto, S Uchida, M Yamaura, H Yoshida, Zhakhovskii, V, Y Izawa

2003 IEEE LEOS ANNUAL MEETING CONFERENCE PROCEEDINGS, VOLS 1 AND 2 297 - 298 2003

Study on EUV emission properties of laser-produced plasma at ILE, Osaka Reviewed

M Nakai, H Nishimura, K Shigemori, N Miyanaga, T Norimatsu, K Nagai, R Matsui, T Hibino, T Okuno, FS Sohbatzadeh, Y Tao, K Hashimoto, M Yamaura, S Fujioka, H Nagatomo, Zhakhovckii, V, K Nishihra, S Uchida, Y Shimada, H Furukawa, M Nakatsuka, Y Izawa

LASER-GENERATED AND OTHER LABORATORY X-RAY AND EUV SOURCES, OPTICS, AND APPLICATIONS 5196 289 - 297 2003

A new research project on extreme ultraviolet (EUV) source development has just been started at the Institute of Laser Engineering, Osaka University. The main task of this project is to find a scientific basis for generating efficient, high-quality, high power EUV plasma source for semiconductor industry. A set of experimental data is to be provided to develop a detailed atomic model included in computer code through experiments using GEKKO-XII high power laser and smaller but high-repetitive lasers. Optimum conditions for efficient EUV generation will be investigated by changing properties of lasers and targets. As the,first step of the experiments, spherical solid tin and tin-oxide. targets were illuminated uniformly with twelve beams from the GEKKO XII. It has been confirmed that maximum conversion efficiency into 13.5 nm EUV light is achieved at illumination intensity less than 2 x 10(11) W/cm(2). No significant difference is found between laser wavelengths of one pm and a half mum. Density structure of the laser-irradiated surface of a planar tin target has been measured experimentally at 10(12) W/cm(2) to show formation of double ablation structure with density plateau by thermal radiation transport. An opacity experiment has just been initiated.

Nuclear fusion - Fast heating scalable to laser fusion ignition Reviewed

R Kodama, H Shiraga, K Shigemori, Y Toyama, S Fujioka, H Azechi, H Fujita, H Habara, T Hall, Y Izawa, T Jitsuno, Y Kitagawa, KM Krushelnick, KL Lancaster, K Mima, K Nagai, M Nakai, H Nishimura, T Norimatsu, PA Norreys, S Sakabe, KA Tanaka, A Youssef, M Zepf

NATURE 418 ( 6901 ) 933 - 934 2002.8

Penumbral imaging for measurement of the ablation density in laser-driven targets Reviewed

S Fujioka, H Shiraga, M Nishikino, M Heya, K Shigemori, M Nakai, H Azechi, S Nakai, T Yamanaka

REVIEW OF SCIENTIFIC INSTRUMENTS 73 ( 7 ) 2588 - 2596 2002.7

One-dimensional (1D) penumbral imaging technique with high spatial resolution has been developed, and applied to density profile measurements in laser-driven Rayleigh-Taylor instability experiments at a GEKKO XII-HIPER laser system. A laser-irradiated planar target was observed with side-on x-ray backlighting. A penumbral image of an x-ray radiograph was made by using a knife-edge imager. The x-ray radiograph was, then, reconstructed by differentiating the penumbral image with a proper Wiener filtering. A density profile was deduced from the reconstructed x-ray radiograph. In a proof-of-principle experiment, the density profile of a polystyrene (PS) target before laser irradiation was measured by using this method, and high spatial resolution of 3-4 mum was demonstrated. A laser-irradiated PS target in the acceleration phase was observed. The experimentally observed density profile was found to be consistent with the prediction by a 1D hydrodynamic simulation code. The x-ray penumbral imaging is a very simple and useful technique with high spatial resolution for research in hydrodynamics relevant to inertial fusion energy. (C) 2002 American Institute of Physics.

Single spatial mode experiments on initial laser imprint on direct-driven planar targets Reviewed

M Nakai, H Azechi, N Miyanaga, K Shigemori, T Kawasaki, T Nagaya, M Nishikino, Y Kanai, D Ohnuki, H Nishimura, H Shiraga, O Maegawa, R Ishizaki, K Nishihara, H Takabe, T Yamanaka

PHYSICS OF PLASMAS 9 ( 5 ) 1734 - 1744 2002.5

Flat plastic targets were directly irradiated and accelerated by partially coherent light from the GEKKO XII laser [Yamanaka , IEEE J. Quantum Electron. QE-17, 1639 (1981)] with the wavelength of 0.53 mum in order to investigate initial laser imprinting. The growth of the perturbation imprinted on the target by an initial foot pulse modulated with a single spatial frequency was observed by the face-on x-ray backlight technique. Imprint levels produced by the foot beam with a stationary intensity modulation of the illumination profile and with a dynamically changing modulation were successfully obtained by an image relay technique and the improved two-wavelength Young's interference method. Simple analytic models are proposed and compared with the experimental results. Stationary imprinting with perturbation wavelength longer than the target thickness is found to be well described by a simple incompressible model. The dynamic dependence of the imprint on the time scale of the temporal illumination profile is found to be qualitatively explained by linear perturbation analysis. (C) 2002 American Institute of Physics.

Imprint reduction in a plasma layer preformed with x-ray irradiation Reviewed

M Nishikino, H Shiraga, N Miyanaga, N Ohnishi, K Shigemori, S Fujioka, M Nakai, H Nishimura, H Azechi, K Mima, H Takabe, S Nakai, T Yamanaka

PHYSICS OF PLASMAS 9 ( 4 ) 1381 - 1391 2002.4

Indirect-direct-hybrid irradiation scheme has been proposed for suppressing the initial imprint of the laser irradiation nonuniformities. The target is irradiated by a low intensity x-ray radiation prior to the direct-drive laser pulse. The x-ray irradiation generates a plasma expansion layer on the target surface. The thermal smoothing effect is expected to take place in the preformed plasma when the direct-drive laser pulse comes onto the target, and then, the initial imprint can be significantly reduced. Planar target experiments on the indirect-direct-hybrid irradiation scheme were performed. The preformed plasma profile was measured by using x-ray side-on backlighting method. The reduction of the initial imprint was demonstrated by the indirect-direct-hybrid irradiation scheme on planar target experiments. The imprint is suppressed by a factor of 1.5-7 depending on x-ray preirradiation conditions. Results are in good agreement with the cloudy-day model with parameters derived from one-dimensional simulation. (C) 2002 American Institute of Physics.

Perturbation transfer from the front to rear surface of laser-irradiated targets Reviewed

K Shigemori, H Azechi, M Nakai, T Endo, T Nagaya, T Yamanaka

PHYSICAL REVIEW E 65 ( 4 ) 2002.4

We present experimental results on the perturbation transfer of laser irradiated planar foils. Perturbed polystyrene foils were irradiated directly by laser at intensity of 6x10(13) W/cm(2). We measured perturbations on the foils by side-on x-ray backlighting technique. Perturbations on the rear surface due to the rippled shock front were observed just after the shock breakout. We also observed feedthrough of perturbations on the laser-irradiated surface that grows due to the Rayleigh-Taylor instability.

Ablative Rayleigh-Taylor instability at short wavelengths observed with moire interferometry Reviewed

T Sakaiya, H Azechi, M Matsuoka, N Izumi, M Nakai, K Shigemori, H Shiraga, A Sunahara, H Takabe, T Yamanaka

PHYSICAL REVIEW LETTERS 88 ( 14 ) 2002.4

One of the most important quantities to be measured for better understanding of the ablative Rayleigh-Taylor (RT) instability is the growth rate in the short wavelength region at which the RT instability is significantly reduced. The short wavelength (4.7-12 mum) RT growth rates for direct-drive targets were measured for the first time by utilizing the innovated moire interferometry [M. Matsuoka et al., Rev. Sci. Instrum. 70, 637 (1999)]. These growth rates were reasonably well reproduced by the simulation that solves the Fokker-Planck equation for nonlocal heat transport.

Perturbation transfer from the front to rear surface of laser-irradiated targets Reviewed

K. Shigemori, H. Azechi, M. Nakai, T. Endo, T. Nagaya, T. Yamanaka

Physical Review E - Statistical, Nonlinear, and Soft Matter Physics 65 ( 4 ) 045401/4 2002.4

We present experimental results on the perturbation transfer of laser irradiated planar foils. Perturbed polystyrene foils were irradiated directly by laser at intensity of 6 × 1013 W/cm2. We measured perturbations on the foils by side-on x-ray backlighting technique. Perturbations on the rear surface due to the rippled shock front were observed just after the shock breakout. We also observed feedthrough of perturbations on the laser-irradiated surface that grows due to the Rayleigh-Taylor instability. © 2002 The American Physical Society.

Perturbation transfer from the front to rear surface of laser-irradiated targets Reviewed

K. Shigemori, H. Azechi, M. Nakai, T. Endo, T. Nagaya, T. Yamanaka

Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics 65 ( 4 ) 4 2002

We present experimental results on the perturbation transfer of laser irradiated planar foils. Perturbed polystyrene foils were irradiated directly by laser at intensity of [formula presented] We measured perturbations on the foils by side-on x-ray backlighting technique. Perturbations on the rear surface due to the rippled shock front were observed just after the shock breakout. We also observed feedthrough of perturbations on the laser-irradiated surface that grows due to the Rayleigh-Taylor instability. © 2002 The American Physical Society.

Rayleigh Taylor and laser imprinting diagnostics Reviewed

H Azechi, M Nakai, K Shigemori, N Izumi, H Shiraga, M Nishikino, T Sakaiya, S Fujioka, Y Tamari, N Miyanaga, H Nishimura

ADVANCED DIAGNOSTICS FOR MAGNETIC AND INERTIAL FUSION 169 - 176 2002

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Papers - Nakai Mitsuo