Kumada, Takayuki; Otobe, Tomohito; Nishikino, Masaharu; Hasegawa, Noboru; Hayashi, Terutake*
Applied Physics Letters, 108(1), p.011102_1 - 011102_4, 2016/01
The dynamics of photomechanical spallation during femtosecond laser ablation of fused silica was studied by time-resolved reflectivity with double pump pulses. Oscillation of reflectivity was caused by interference between the probe pulses reflected at the sample surface and the spallation layer, and was enhanced when the surface is irradiated with the second pump pulse within a time interval of several picoseconds after the first pump pulse. However, as the time-interval was increased, the oscillation amplitude decreased with an exponential decay time of 10 ps. The oscillation disappeared when the interval exceeded 20 ps. This result suggests that the formation time of the spallation layer is approximately 10 ps.
Nishikino, Masaharu; Ishino, Masahiko; Ichimaru, Satoshi*; Hatayama, Masatoshi*; Hasegawa, Noboru; Kawachi, Tetsuya
Reza Gakkai Dai-483-Kai Kenkyukai Hokoku; Tanhacho Ryoshi Bimu Hassei To Sono Oyo, p.25 - 28, 2015/12
X-ray ablation has been recently achieved using plasma soft X-ray lasers (SXRLs), laser plasma soft X-rays, and X-ray free electron lasers. In order to study the interactions between picosecond SXRL beams and material and multi-layered structure surfaces were irradiated with SXRL pulse. Following irradiation, the substrate surface was observed using a scanning electron microscope and an atomic force microscope. The surface modifications caused by the SXRL beam were clearly seen. The multi-layered mirror is the important component for the EUV lithography. Then, we have started the damage test of multi-layered structure, and the surface modifications caused by the SXRL pulse irradiations were confirmed.
Pikuz, T.*; Faenov, A.*; Matsuoka, Takeshi*; Matsuyama, Satoshi*; Yamauchi, Kazuto*; Ozaki, Narimasa*; Albertazzi, B.*; Inubushi, Yuichi*; Yabashi, Makina*; Tono, Kensuke*; et al.
Scientific Reports (Internet), 5, p.17713_1 - 17713_10, 2015/12
Namba, Shinichi*; Hasegawa, Noboru; Kishimoto, Maki; Nishikino, Masaharu; Ishino, Masahiko; Kawachi, Tetsuya
AIP Advances (Internet), 5(11), p.117101_1 - 117101_10, 2015/11
To characterize the temporal evolution of ultrashort X-ray pulses emitted by laser plasmas using a pump-probe method, a magnetic bottle time-of-flight electron spectrometer is constructed. The design is determined by numerical calculations of a mirror magnetic field and of the electron trajectory in a flight tube. The performance of the spectrometer is characterized by measuring the electron spectra of xenon atoms irradiated with a laser-driven plasma X-ray pulse. In addition, as a preliminary experiment, two-color above-threshold ionization (ATI) is conducted, in which xenon atoms are simultaneously irradiated with an X-ray laser pump and an IR laser probe. The correlation in the intensity of the Auger sideband spectra and in the time delay of the two laser pulses yields an X-ray pulse width of 5.7 ps, in good agreement with the value obtained using an X-ray streak camera.
Kim, C. M.*; Steil, H.*; Matou, B.*; Nishikino, Masaharu; Hasegawa, Noboru; Kawachi, Tetsuya; Tran, K. A.*; Janulewicz, K. A.*
Physical Review A, 92(4), p.043807_1 - 043807_7, 2015/10
We present polarization measurement of a Ni-like Ag X-ray laser working in the transient collisional excitation scheme. A calibrated membrane multilayer beam splitter was used to determine the energies of two mutually perpendicular polarization components (s and p components). As a result, we observed a high degree of polarization that fluctuated from shot to shot. The dominant polarization component switched from s to p when pumping was made stronger. The measurement results are discussed from the point of view of the general polarization theory and supported by a numerical simulation based on Maxwell-Bloch equations.
Dinh, T.-H.*; Suzuki, Yuhei*; Arai, Goki*; Li, B.*; Dunne, P.*; O'Sullivan, G.*; Fujioka, Shinsuke*; Hasegawa, Noboru; Kawachi, Tetsuya; Nishikino, Masaharu; et al.
Applied Physics Letters, 107(12), p.121101_1 - 121101_5, 2015/09
Ishino, Masahiko; Hasegawa, Noboru; Nishikino, Masaharu; Pikuz, T.*; Skobelev, I. Y.*; Faenov, A.*; Inogamov, N.*; Kawachi, Tetsuya; Yamagiwa, Mitsuru
X-Ray Lasers and Coherent X-Ray Sources; Development and Applications XI (Proceedings of SPIE, Vol.9589), p.958904_1 - 958904_6, 2015/09
To study the ablation process induced by the soft X-ray laser pulse, we investigated the electron temperature of the ablating material. Focused soft X-ray laser pulses having a wavelength of 13.9 nm and duration of 7 ps were irradiated onto target surfaces, and we observed the optical emission from surfaces by use of an optical camera. On target surfaces, we could confirm damage structures, but no emission signal in the visible spectral range during ablation could be observed. Then, we estimated the electron temperature in the ablating matter, and we estimated the electron temperature to be lower than 1 eV and the process duration was shorter than 1000 ps. This result is in good accordance with the theoretical prediction. Our investigation implies that the spallative ablation occurs in the low electron temperature region of a non-equilibrium state of warm dense matter. We will present the current state of our eperimental results.
Nishikino, Masaharu; Kawachi, Tetsuya; Hasegawa, Noboru; Ishino, Masahiko; Minami, Yasuo*; Suemoto, Toru*; Onishi, Naofumi*; Ito, Atsushi*; Sato, Katsutoshi*; Faenov, A.*; et al.
X-Ray Lasers and Coherent X-Ray Sources; Development and Applications XI (Proceedings of SPIE, Vol.9589), p.958902_1 - 958902_7, 2015/09
Hasegawa, Noboru; Nishikino, Masaharu; Tomita, Takuro*; Onishi, Naofumi*; Ito, Atsushi*; Eyama, Tsuyoshi*; Kakimoto, Naoya*; Izutsu, Rui*; Minami, Yasuo*; Baba, Motoyoshi*; et al.
X-Ray Lasers and Coherent X-Ray Sources; Development and Applications XI (Proceedings of SPIE, Vol.9589), p.95890A_1 - 95890A_8, 2015/09
We have improved a soft X-ray laser (SXRL) interferometer synchronized with a Ti:Sapphire laser pulse to observe the single-shot imaging of the nano-scaled structure dynamics of the laser induced materials. By the precise imaging optics and double time fiducial system having been installed, the lateral resolution on the sample surface and the precision of the temporal synchronization between the SXRL and Ti:Sapphire laser pulses were improved to be 700 nm and 2 ps, respectively. By using this system, the initial stage (before 200 ps) of the ablation process of the Pt surface pumped by 80 fs Ti:Sapphire laser pulse was observed by the comparison between the soft X-ray reflective image and interferogram. We have succeeded in the direct observation of the unique ablation process around the ablation threshold such as the rapid increase of the surface roughness and surface vibration.
Janulewicz, K. A.*; Kim, C. M.*; Steil, H.*; Kawachi, Tetsuya; Nishikino, Masaharu; Hasegawa, Noboru
X-Ray Lasers and Coherent X-Ray Sources; Development and Applications XI (Proceedings of SPIE, Vol.9589), p.95890N_1 - 95890N_7, 2015/09
We describe measurement results on the polarization state of amplified spontaneous emission signal from a collisionally pumped Ni-like Ag soft X-ray laser with a transient inversion. The result obtained with a calibrated membrane beam splitter as a polarization state (P-state) selector shows that dominance one of the mutually perpendicular electric field components (p- or s-) in the output signal depends on the hydrodynamic state of the plasma medium. Two different hydrodynamic states were referred as a low gain and high gain regimes and the allocated P-states had dominant s- and p-component, respectively. It was also shown that due to correlations between p- and s-components in the process of coherent amplification of noise, correct description of the polarization state requires applying the generalized theory of polarization and formulated there the generalized degree of polarization.
Nishikino, Masaharu; Hasegawa, Noboru; Ishino, Masahiko; Ochi, Yoshihiro; Kawachi, Tetsuya; Yamagiwa, Mitsuru; Kato, Yoshiaki*
Chinese Optics Letters, 13(7), p.070002_1 - 070002_3, 2015/07
Hasegawa, Noboru; Tomita, Takuro*; Nishikino, Masaharu; Eyama, Tsuyoshi*; Kakimoto, Naoya*; Minami, Yasuo*; Baba, Motoyoshi*; Onishi, Naofumi*; Ito, Atsushi*; Kawachi, Tetsuya; et al.
JAEA-Conf 2015-001, p.17 - 20, 2015/07
We have succeeded in simultaneous observation of the ablation front and the expansion front with thin filmy structure in the femto-second laser ablation process of a gold target by using the 13.9 nm soft X-ray probe (incident angle to the sample 70 deg) with soft X-ray interferometer. The dependence on the laser local fluence and materials was obtained by the comparison between gold and tungsten.
Sato, Katsutoshi*; Nishikino, Masaharu; Kawachi, Tetsuya; Shimokawa, Takashi*; Imai, Takashi*; Teshima, Teruki*; Nishimura, Hiroaki*; Kando, Masaki
Journal of Radiation Research, 56(4), p.633 - 638, 2015/07
While X-ray laser is expected to be widely applied to biomedical studies, this has not been achieved to date and its biological effects such as DNA damage have not been evaluated. As a first step for its biological application, we developed a culture cell irradiation system using laser-plasma soft X-ray laser and investigated whether the soft X-ray laser is able to induce the DNA double strand breaks (DSBs) in living cells or not. The human adenocarcimona cell line A549 was irradiated with the soft X-ray laser at a photon energy of 89 eV and then the repair focus formation of the DSBs was assessed by immunofluorescence staining with anti-phosphorylated DNA-PKcs antibody. As a result, the phosphorylated DNA-PKcs foci were clearly identified even with just a single shot of the soft X-ray laser. In this study, we successfully demonstrated for the first time that soft X-ray laser at 89 eV induced the DNA double strand breaks in living cells.
Inogamov, N. A.*; Zhakhovsky, V. V.*; Hasegawa, Noboru; Nishikino, Masaharu; Yamagiwa, Mitsuru; Ishino, Masahiko; Agranat, M. B.*; Ashitkov, S. I.*; Faenov, A. Y.*; Khokhlov, V. A.*; et al.
Applied Physics B, 119(3), p.413 - 419, 2015/06
Kumada, Takayuki; Akagi, Hiroshi; Itakura, Ryuji; Otobe, Tomohito; Nishikino, Masaharu; Yokoyama, Atsushi
Applied Physics Letters, 106(22), p.221605_1 - 221605_5, 2015/06
The dynamics of femtosecond laser ablation of transparent polymers were examined using time-resolved reflectivity. When these polymers were irradiated by a pump pulse with fluence above the ablation threshold of 0.8-2.0 J/cm, we observed the oscillation of the reflectivity caused by the interference between the reflected probe pulses from the sample surface and the thin layer due to the non-thermal photomechanical effects of spallation. As the fluence of the pump pulse increased, the separation velocity of the thin layer increased from 6 km/s to an asymptotic value of 11 km/s. It is suggested that the velocities are determined by shock-wave velocities of the photo-excited layer.
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
Nishikino, Masaharu; Hasegawa, Noboru; Tomita, Takuro*; Eyama, Tsuyoshi*; Kakimoto, Naoya*; Onishi, Naofumi*; Ito, Atsushi*; Baba, Motoyoshi*; Minami, Yasuo*; Kawachi, Tetsuya; et al.
Reza Gakkai Dai-471-Kai Kenkyukai Hokoku; Tanhacho Ryoshi Bimu Hassei To Sono Oyo, p.9 - 12, 2014/12
no abstracts in English
Ishino, Masahiko; Hasegawa, Noboru; Nishikino, Masaharu; Pikuz, T. A.*; Skobelev, I. Y.*; Faenov, A.*; Inogamov, N. A.*; Kawachi, Tetsuya; Yamagiwa, Mitsuru
Journal of Applied Physics, 116(18), p.183302_1 - 183302_6, 2014/11
We investigated the optical emission from the ablating surfaces induced by the irradiations of soft X-ray laser (SXRL) pulses with the aim of estimation of the maximum electron temperature. No emission signal in the spectral range of 400-800 nm could be observed despite the formation of damage structures on the target surfaces. Hence, we estimated an upper limit for the electron temperature of 0.4-0.7 eV for the process duration of 100-1000 ps. Our results imply that the ablation and/or surface modification by the SXRL is not accompanied by plasma formation but is induced by thermo-mechanical pressure, which is so called a spallative ablation. This spallative ablation process occurs in the low electron temperature region of a non-equilibrium state of warm dense matter.
Arita, Ren*; Nakazato, Tomoharu*; Shimizu, Toshihiko*; Yamanoi, Kohei*; Empizo, M.*; Hori, Tatsuhiro*; Fukuda, Kazuhito*; Minami, Yuki*; Sarukura, Nobuhiko*; Maruyama, Momoko; et al.
Optical Materials, 36(12), p.2012 - 2015, 2014/10
A single shot image of a ZnO crystal excited by the EUV laser of Kansai Photon Science Institute was captured. The evaluated EUV beam waist radii from the ZnO emission pattern along the horizontal and vertical axes are 5.0 and 4.7m, respectively. The expected focal spot size of EUV laser and the spatial resolution of the magnifier (including the Schwarzschild objectives and lenses) are however 1 and 4m, respectively. The discrepancy on the spatial resolutions is attributed to exciton diffusion. We estimated the ZnO exciton diffusion length from the effective decay time which is shortened by exciton-exciton collision quenching and which is dependence on excitation energy density. Our results indicate that the short lifetime of ZnO is required to improve the spatial resolution.
Kawachi, Tetsuya; Nishikino, Masaharu; Daido, Hiroyuki
Purazuma, Kaku Yugo Gakkai-Shi, 90(9), P. 579, 2014/09
no abstracts in English