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Journal Articles

Modeling of initial interaction between the laser pulse and Sn droplet target and pre-plasma formation for the LPP EUV source

Sasaki, Akira; Nishihara, Katsunobu*; Sunahara, Atsushi*; Nishikawa, Takeshi*

Proceedings of SPIE, Vol.9776, p.97762C_1 - 97762C_6, 2016/03

 Times Cited Count:1 Percentile:55.81

For the improvement of efficiency and output of the laser pumped plasma (LPP) extreme ultra-violet (EUV) light source, we present a hydrodynamics model of laser irradiated Sn targets. The model takes liquid/solid to gas transition and mixed phase condition of the flow into account for the calculation of the distribution of the particles produced by the pre-pulse laser irradiation and optimization of the EUV source. Firstly, we investigate the mechanisms of the fragmentation of the target and particle emission, including the effect of the equation of state of Sn, and secondly, an applicable model is proposed based on the analysis.

Journal Articles

Density and X-ray emission profile relationships in highly ionized high-Z laser-produced plasmas

Yoshida, Kensuke*; Fujioka, Shinsuke*; Higashiguchi, Takeshi*; Ugomori, Teruyuki*; Tanaka, Nozomi*; Kawasaki, Masato*; Suzuki, Yuhei*; Suzuki, Chihiro*; Tomita, Kentaro*; Hirose, Ryoichi*; et al.

Applied Physics Letters, 106(12), p.121109_1 - 121109_5, 2015/03

 Times Cited Count:6 Percentile:30.43(Physics, Applied)

Journal Articles

Efficient extreme ultraviolet emission from one-dimensional spherical plasmas produced by multiple lasers

Yoshida, Kensuke*; Fujioka, Shinsuke*; Higashiguchi, Takeshi*; Ugomori, Teruyuki*; Tanaka, Nozomi*; Ohashi, Hayato*; Kawasaki, Masato*; Suzuki, Yuhei*; Suzuki, Chihiro*; Tomita, Kentaro*; et al.

Applied Physics Express, 7(8), p.086202_1 - 086202_4, 2014/08

 Times Cited Count:25 Percentile:74.19(Physics, Applied)

We demonstrate high conversion efficiency for extreme ultraviolet (EUV) emission at 6.5-6.7 nm from multiple laser beam-produced one-dimensional spherical plasmas. Multiply charged-state ions produce strong resonance emission lines, which combine to yield intense unresolved transition arrays in Gd, Tb, and Mo. The maximum in-band EUV conversion efficiency was observed to be 0.8%, which is one of the highest values ever reported due to the reduction of plasma expansion loss.

Journal Articles

Prepulse and amplified spontaneous emission effects on the interaction of a petawatt class laser with thin solid targets

Esirkepov, T. Z.; Koga, J. K.; Sunahara, Atsushi*; Morita, Toshimasa; Nishikino, Masaharu; Kageyama, Kei*; Nagatomo, Hideo*; Nishihara, Katsunobu; Sagisaka, Akito; Kotaki, Hideyuki; et al.

Nuclear Instruments and Methods in Physics Research A, 745, p.150 - 163, 2014/05

 Times Cited Count:40 Percentile:96.69(Instruments & Instrumentation)

Journal Articles

Atomic processes and radiation hydrodynamics

Sasaki, Akira; Sunahara, Atsushi*; Nishihara, Katsunobu*

Purazuma, Kaku Yugo Gakkai-Shi, 89(10), p.654 - 658, 2013/10

no abstracts in English

Journal Articles

Modeling of atomic processes of multiple charged ions in plasmas and its application to the study of EUV light sources

Sasaki, Akira; Nishihara, Katsunobu*; Sunahara, Atsushi*; Furukawa, Hiroyuki*; Nishikawa, Takeshi*; Koike, Fumihiro*

Plasma and Fusion Research (Internet), 6(Sp.1), p.2401145_1 - 2401145_4, 2011/12

Atomic processes and radiation from multiple charged ions in plasmas are of the interest in the investigation of plasma wall interaction and transport of impurity ions in the fusion devices. The emission from multiple charged ions is also investigated for the development of extreme ultra violet light (EUVL) sources at $$lambda=13.5 nm$$. Efficient emission through the 4d-4f + 4p-4d transition array is obtained from tin ions. An optimization of pumping conditions of laser produced plasma sources is carried out theoretically and experimentally. We also investigate an extension of the plasma light sources to short wavelength to $$lambda=6.5 nm$$ using Gd and Tb plasmas. We discuss requirements to the atomic structure, rate coefficient and collisional radiative codes to determine ion abundance and level population as a function of plasma temperature and density, to calculate the radiation intensity as well as emission spectrum.

Journal Articles

Efficient multi-keV X-ray generation from a high-Z target irradiated with a clean ultra-short laser pulse

Zhang, Z.*; Nishikino, Masaharu; Nishimura, Hiroaki*; Kawachi, Tetsuya; Pirozhkov, A. S.; Sagisaka, Akito; Orimo, Satoshi; Ogura, Koichi; Yogo, Akifumi; Okano, Yasuaki*; et al.

Optics Express (Internet), 19(5), p.4560 - 4565, 2011/02

 Times Cited Count:17 Percentile:65.65(Optics)

$$Kalpha$$ line emission from Mo and Ag plate were experimentally studied by using ultra-high intensity, clean femtosecond laser pulses. Absolutely yield of $$Kalpha$$ X-rays at 17 keV from Mo and 22 keV from Ag were measured as a function of the laser pulse contrast ratio and irradiation intensity. Significant enhancement of $$Kalpha$$ yields were obtained for both Mo and Ag with higher contrast ratios and high irradiance. The conversion efficiencies of 4.28 $$times$$ 10$$^{-5}$$/sr for Mo and 4.84 $$times$$ 10$$^{-5}$$/sr for Ag, the highest values ever obtained, have been demonstarted with the contrast ratio of 10$$^{-10}$$ to 10$$^{-11}$$.

Journal Articles

Theoretical investigation of the spectrum and conversion efficiency of short wavelength extreme-ultraviolet light sources based on terbium plasmas

Sasaki, Akira; Nishihara, Katsunobu*; Sunahara, Atsushi*; Furukawa, Hiroyuki*; Nishikawa, Takeshi*; Koike, Fumihiro*

Applied Physics Letters, 97(23), p.231501_1 - 231501_3, 2010/12

 Times Cited Count:14 Percentile:52.5(Physics, Applied)

Emission spectrum and conversion efficiency of laser produced terbium plasmas are investigated theoretically on the basis of computational atomic data. It is shown that calculation reproduces the main peak of the experimental spectrum at $$lambda=6.5$$nm, which originates from 4$$d$$-4$$f$$ transitions of near palladium like ions (Tb$$^{19+}$$). Simple model of the isothermal expansion of plasma suggests that efficient emission can be obtained by pumping a plasma with a laser pulse with an intensity approximately one order of magnitude grater than in the case of tin sources at $$lambda=13.5$$nm.

Journal Articles

FIREX project and effects of self-generated electric and magnetic fields on electron-driven fast ignition

Mima, Kunioki*; Sunahara, Atsushi*; Shiraga, Hiroyuki*; Nishimura, Hiroaki*; Azechi, Hiroshi*; Nakamura, Tatsufumi; Jozaki, Tomoyuki*; Nagatomo, Hideo*; Garcia, C.*; Veralde, P.*

Plasma Physics and Controlled Fusion, 52(12), p.124047_1 - 124047_6, 2010/12

 Times Cited Count:9 Percentile:36.17(Physics, Fluids & Plasmas)

Fast ignition is a new scheme in laser fusion, in which higher energy gain with a smaller laser pulse energy is expected. At Osaka University, a laser with four beams and a total output of 10 kJ ps-1, laser for fast ignition experiment (LFEX), has been constructed and we have carried out an integrated experiment with one beam of the LFEX. Through experiments it was found that the coupling efficiency is degraded when the laser pre-pulse is not sufficiently small. Furthermore, the distance between the hot electron source and the core plasma is large. In this paper it is proposed that a thin foil covers the laser entrance of the cone to mitigate the pre-plasma and a double cone reduces the loss of high energy electrons from the side wall of the cone. The simulations indicate that a higher coupling efficiency is expected for the double cone target with a thin foil at the laser entrance.

Journal Articles

Modeling of radiative properties of Sn plasmas for extreme-ultraviolet source

Sasaki, Akira; Sunahara, Atsushi*; Furukawa, Hiroyuki*; Nishihara, Katsunobu*; Fujioka, Shinsuke*; Nishikawa, Takeshi*; Koike, Fumihiro*; Ohashi, Hayato*; Tanuma, Hajime*

Journal of Applied Physics, 107(11), p.113303_1 - 113303_11, 2010/06

 Times Cited Count:33 Percentile:77.65(Physics, Applied)

Atomic processes in Sn plasmas are investigated for application to extreme-ultraviolet (EUV) light sources used in microlithography. An atomic model of Sn is developed on the basis of calculated atomic data using the Hebrew University Lawrence Livermore Atomic Code (HULLAC). Resonance and satellite lines from singly and multiply excited states of Sn ions are identified. The wavelengths of the 4$$d$$-4$$f$$ + 4$$p$$-4$$d$$ transitions of Sn$$^{5+}$$ to Sn$$^{13+}$$ are investigated. Results of calculation are compared with those of the charge exchange spectroscopy, measurement of the emission spectrum of the laser produced plasma EUV source, and the opacity measurement of a radiatively heated Sn sample. A reasonable agreement is observed between calculated and experimental EUV emission spectra. The spectral emissivity and opacity of Sn plasmas are calculated using a full collisional radiative (CR) model as a function of electron temperature and ion density.

Journal Articles

Atomic modeling of the plasma EUV sources

Sasaki, Akira; Sunahara, Atsushi*; Furukawa, Hiroyuki*; Nishihara, Katsunobu*; Nishikawa, Takeshi*; Koike, Fumihiro*; Tanuma, Hajime*

High Energy Density Physics, 5(3), p.147 - 151, 2009/09

 Times Cited Count:9 Percentile:35.94(Physics, Fluids & Plasmas)

We study the radiative properties of the EUV source to address conditions to achieve an output power and efficiency required for its application to the next generation microlithography. An atomic model is developed based on the atomic data calculated by Hullac code, which is validated through detailed comparisons with experimental emission and a absorption spectra. The atomic model is improved with respect to the wavelength of the strong emission lines, and the number of satellite channels taken into account. As a result, the radiation hydrodynamics model is shown to successfully reproduce the experiments. We show Sn plasma is more efficient than Xe plasma because of the atomic number dependence of the emission wavelength, and the use of CO$$_{2}$$ lasers as a pumping source has an advantage to reduce satellite contribution and to have narrower emission spectrum to obtain higher conversion efficiency.

Journal Articles

The Atomic model of the Sn plasmas for the EUV sources

Sasaki, Akira; Sunahara, Atsushi*; Nishihara, Katsunobu*; Nishikawa, Takeshi*; Koike, Fumihiro*; Tanuma, Hajime*

Journal of Physics; Conference Series, 163, p.012107_1 - 012107_4, 2009/06

 Times Cited Count:5 Percentile:85.6

no abstracts in English

Journal Articles

Atomic processes in the LPP and LA-DPP EUV sources

Sasaki, Akira; Nishihara, Katsunobu*; Sunahara, Atsushi*; Furukawa, Hiroyuki*; Nishikawa, Takeshi*; Koike, Fumihiro*

Alternative Lithographic Technologies (Proceedings of SPIE Vol.7271), p.727130_1 - 727130_8, 2009/03

We investigate characteristic feature of the atomic radiation from tin plasmas, which allow one to obtain high power EUV emission efficiently. We develop a collisional radiative model of tin ions to calculate steady-state and time dependent ion abundance, level population, and coefficients of radiative transfer of the plasma. The model, which is based atomic data calculated using the Hullac code is refined both theoretically and experimentally. Calculation of the spectral emissivity and opacity are carried out over a wide range of plasma density and temperature, and pumping conditions to obtain high conversion efficiency are discussed.

Journal Articles

Modeling of the atomic processes and photo emission of the plasmas for the EUV source

Sasaki, Akira; Sunahara, Atsushi*; Nishihara, Katsunobu*; Nishikawa, Takeshi*; Koike, Fumihiro*; Tanuma, Hajime*

Reza Kenkyu, 36(Suppl.), p.1132 - 1135, 2008/11

no abstracts in English

Journal Articles

Atomic model and optimization of EUV light source

Nishihara, Katsunobu*; Sunahara, Atsushi*; Sasaki, Akira; Tanuma, Hajime*; Koike, Fumihiro*; Fujioka, Shinsuke*; Nishimura, Hiroaki*; Shimada, Yoshinori*

Reza Kenkyu, 36(11), p.690 - 699, 2008/11

The critical issue for realization of a laser produced plasma (LPP) extreme ultraviolet (EUV) light source is the conversion efficiency (CE) from incident laser power to EUV radiation of 13.5 nm wavelength. From an atomic physics, we show that tin is the most suitable radiation material compared with xenon and lithium. We also show the optimization of laser and target conditions to obtain high CE using a power balance model. We propose a double-pulse irradiation scheme for high CE using a carbon dioxides laser and a droplet target.

Journal Articles

Optimization of extreme ultraviolet emission from laser-produced tin plasmas based on radiation hydrodynamics simulations

Sunahara, Atsushi*; Nishihara, Katsunobu*; Sasaki, Akira

Plasma and Fusion Research (Internet), 3, p.043_1 - 043_5, 2008/08

no abstracts in English

Journal Articles

Detailed atomic modeling of Sn plasmas for the EUV source

Sasaki, Akira; Sunahara, Atsushi*; Nishihara, Katsunobu*; Nishikawa, Takeshi*; Koike, Fumihiro*; Tanuma, Hajime*

Journal of Physics; Conference Series, 112, p.042062_1 - 042062_4, 2008/00

 Times Cited Count:4 Percentile:85.41

no abstracts in English

Journal Articles

Two dimensional radiation hydrodynamic simulation for extreme ultra-violet emission from laser-produced tin plasmas

Sunahara, Atsushi*; Sasaki, Akira; Nishihara, Katsunobu*

Journal of Physics; Conference Series, 112, p.042048_1 - 042048_4, 2008/00

 Times Cited Count:19 Percentile:98.39

We simulated Extreme Ultra-Violet (EUV) emission from laser-produced tin plasmas for the lithography of semi-conductor, using one- and two- dimensional radiation hydrodynamic simulation codes, and benchmarked the simulations by comparison with recent experiments. We successfully reproduced the measured conversion efficiency, X-ray spectra, and plasma density profiles in the experimental conditions. We found self-absorption of radiation due to the large opacity plays an important role in emission.

Journal Articles

EUV light source by high power laser

Izawa, Yasukazu*; Nishihara, Katsunobu*; Tanuma, Hajime*; Sasaki, Akira; Murakami, Masakatsu*; Sunahara, Atsushi*; Nishimura, Hiroaki*; Fujioka, Shinsuke*; Aota, Tatsuya*; Shimada, Yoshinori*; et al.

Journal of Physics; Conference Series, 112, p.042047_1 - 042047_4, 2008/00

 Times Cited Count:7 Percentile:92.73

In the development of a high power EUV source used in the EUV lithography system, we have been constructed EUV database of laser-produced tin plasma by the theoretical and experimental studies. On the basis of our understanding, the optimum conditions of lasers and plasmas were clarified, and we proposed the guidelines of laser plasma to obtain clean, efficient and high power EUV source for the practical EUV lithography system. In parallel to such studies, novel targets and high power laser system to generate the optimized EUV source plasma have been developed.

Journal Articles

Plasma physics and radiation hydrodynamics in developing an extreme ultraviolet light source for lithography

Nishihara, Katsunobu*; Sunahara, Atsushi*; Sasaki, Akira; Nunami, Masanori*; Tanuma, Hajime*; Fujioka, Shinsuke*; Shimada, Yoshinori*; Fujima, Kazumi*; Furukawa, Hiroyuki*; Kato, Takako*; et al.

Physics of Plasmas, 15(5), p.056708_1 - 056708_11, 2008/00

 Times Cited Count:109 Percentile:97.47(Physics, Fluids & Plasmas)

61 (Records 1-20 displayed on this page)