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Journal Articles

Observation of surface modification of multi-layered mirror induced by soft X-ray laser pulse

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.

Journal Articles

Construction of a magnetic bottle spectrometer and its application to pulse duration measurement of X-ray laser using a pump-probe method

Namba, Shinichi*; Hasegawa, Noboru; Kishimoto, Maki; Nishikino, Masaharu; Ishino, Masahiko; Kawachi, Tetsuya

AIP Advances (Internet), 5(11), p.117101_1 - 117101_10, 2015/11

 Times Cited Count:0 Percentile:100(Nanoscience & Nanotechnology)

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.

Journal Articles

Low electron temperature in ablating materials formed by picosecond soft X-ray laser pulses

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

 Times Cited Count:1 Percentile:36.32

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.

Journal Articles

Observation of dynamics and modification of solid surface using a picosecond soft X-ray laser

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

Journal Articles

Soft X-ray laser observation of femtosecond-laser-driven ablation of tungsten

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

 Times Cited Count:1 Percentile:90.58(Optics)

Journal Articles

Hydrodynamics driven by ultrashort laser pulse; Simulations and the optical pump - X-ray probe experiment

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

 Times Cited Count:6 Percentile:55.3(Optics)

Journal Articles

Applications of multilayered gratings to synchrotron light sources; New horizon of diffraction grating monochromators in the keV region

Koike, Masato; Imazono, Takashi; Ishino, Masahiko

X-sen Bunseki No Shimpo, 46, p.159 - 166, 2015/03

The demand for the physical-properties research using powerful light sources, such as synchrotron radiation and soft-X-rays laser light, is increasing. When promoting such research, it is required to develop efficient soft-X-ray spectrometers suitable for absorption, emission, and fluorescence which are appeared in an energy rage of 1-8 keV. We describe the development of laminar type diffraction gratings which enhance diffraction efficiency remarkably by use of soft-X-ray multilayers instead of single metal layers.

Journal Articles

Very low electron temperature in warm dense matter formed by focused picosecond soft X-ray laser pulses

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

 Times Cited Count:7 Percentile:60.58(Physics, Applied)

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.

Journal Articles

Surface nano-structuring produced by spallation of metal irradiated by an ultrashort laser pulse

Inogamov, N. A.*; Zhakhovsky, V. V.*; Ashitkov, S. I.*; Emirov, Y. N.*; Faenov, A. Y.*; Pikuz, T. A.*; Ishino, Masahiko; Kando, Masaki; Hasegawa, Noboru; Nishikino, Masaharu; et al.

Journal of Physics; Conference Series, 500(11), p.112070_1 - 112070_6, 2014/05

 Times Cited Count:18 Percentile:0.88

The mechanism of formation and geometry of surface structures are discussed for the case of single pulse acting on a well-polished metal surface. We demonstrate that the complex surface nano-structures are formed after laser irradiation due to the thermomechanical spallation of ultrathin surface layer of melt. Spallation is accompanied by a strong foaming of melt followed by breaking of the foam. After several nanoseconds the foam remnants freeze up with formation of complex nano-structures on a target surface.

Journal Articles

Development of soft X-ray microscopy using Fresnel zone plate for observation of laser-induce surface dynamics

Nishikino, Masaharu; Baba, Motoyoshi*; Suemoto, Toru; Hasegawa, Noboru; Ishino, Masahiko; Kaihori, Takeshi; Kawachi, Tetsuya; Yamagiwa, Mitsuru

X-Ray Lasers 2012; Springer Proceedings in Physics, Vol.147, p.199 - 202, 2014/00

 Times Cited Count:0 Percentile:100

The dynamical processes of the laser-induced surface modifications such as laser ablation come to attract much attention for the micro processing by the ultra-short laser pulse. It is difficult to observe these phenomena directly, because they are non-repetitive, unrepeatable, and occur very rapidly (pico-second) in a very small (micron) area. In order to observe the detailed laser-ablation process, we have developed the proto-type reflected soft X-ray microscopy using the Fresnel zone plate. The experimental setup and spatial resolution of the X-ray microscopy will be presented.

Journal Articles

Nano-meter size modification of metal surfaces induced by soft X-ray laser single pulse

Ishino, Masahiko; Faenov, A.*; Tanaka, Momoko; Pikuz, T.; Tamotsu, Satoshi*; Hasegawa, Noboru; Nishikino, Masaharu; Starikov, S. V.*; Stegailov, V. V.*; Norman, G.*; et al.

X-Ray Lasers 2012; Springer Proceedings in Physics, Vol.147, p.121 - 124, 2014/00

 Times Cited Count:0 Percentile:100

Journal Articles

Observation of the laser-induced surface dynamics using the single-shot soft X-ray laser probe

Hasegawa, Noboru; Ochi, Yoshihiro; Kawachi, Tetsuya; Nishikino, Masaharu; Ishino, Masahiko; Imazono, Takashi; Kaihori, Takeshi; Morita, Toshimasa; Sasaki, Akira; Terakawa, Kota*; et al.

X-Ray Lasers 2012; Springer Proceedings in Physics, Vol.147, p.117 - 120, 2014/00

 Times Cited Count:0 Percentile:100

We have developed the femto-second laser pump and soft X-ray laser probe system in order to observe the dynamical processes of the femto-second laser ablation. By using this system, we succeed to obtain the temporal evolution of the soft X-ray reflectivity from the laser induced Pt surface. The results lead that the rate of decrease in the reflectivity of the probe beam has a non-linear relation with the pump laser fluence.

Journal Articles

Measurement of femtosecond laser ablation by soft X-ray laser interferometory and reflective imaging

Nishikino, Masaharu; Hasegawa, Noboru; Ishino, Masahiko; Yamagiwa, Mitsuru; Kawachi, Tetsuya; Minami, Yasuo*; Terakawa, Kota*; Takei, Ryota*; Baba, Motoyoshi*; Suemoto, Toru; et al.

JAEA-Conf 2013-001, p.16 - 19, 2013/09

The dynamics of the femtosecond laser ablation is still not clear at the early stage. Several studies on the time-resolved imaging of femtosecond laser ablation process have been performed on various materials. In this study, we have demonstrated a pump and probe imaging of the metal surface morphology during the femtosecond laser ablation by using the laser-driven plasma induced soft X-ray laser (SXRL) as a probe beam. The pumping laser used for ablation was a Ti:Sapphire laser system based on chirped pulse amplification. The pump beam had a Gaussian profile and the focal spot size on the metal surface was about 70 micron at FWHM. The dependence for the pump laser fluence of the ablation surface expansion and the surface condition (roughness and density gradient) were observed from the soft X-ray interferogram and reflective image, respectively.

Journal Articles

Nano-meter scale modifications on material surfaces induced by soft X-ray laser pulse irradiations

Ishino, Masahiko; Faenov, A.*; Tanaka, Momoko; Tamotsu, Satoshi*; Pikuz, T.; Hasegawa, Noboru; Nishikino, Masaharu; Inogamov, N.*; Skobelev, I.*; Fortov, V.*; et al.

Proceedings of SPIE, Vol.8849, p.88490F_1 - 88490F_8, 2013/09

 Times Cited Count:2 Percentile:20.97

Journal Articles

Observation and theory of X-ray mirages

Magnitskiy, S.*; Nagorskiy, N.*; Faenov, A.*; Pikuz, T.; Tanaka, Momoko; Ishino, Masahiko; Nishikino, Masaharu; Fukuda, Yuji; Kando, Masaki; Kawachi, Tetsuya; et al.

Nature Communications (Internet), 4, p.1936_1 - 1936_7, 2013/06

 Times Cited Count:5 Percentile:70.77(Multidisciplinary Sciences)

Advent of plasma-based transient collisional excitation X-ray lasers allowed us to realize compact coherent X-ray sources, thus opening the way to a wide range of applications. Here we report the observation of unexpected concentric rings in the far-field beam profile at the output of a two-stage plasma-based X-ray laser developed in Japan Atomic Energy Agency, which can be considered as the first manifestation of a mirage phenomenon in X-rays. We have developed a method of solving the Maxwell-Bloch equations, which has allowed to find that the observed phenomenon is due to the emergence in the plasma-amplifier of X-ray mirage in the form of the phase matched coherent virtual point source. The obtained results bring a new insight into physical nature of amplification of X-ray radiation in laser-induced plasma amplifiers and open new opportunities for X-ray plasma diagnostics and extreme UV lithography.

Journal Articles

Observations of surface modifications induced by the multiple pulse irradiation using a soft picosecond X-ray laser beam

Ishino, Masahiko; Faenov, A. Ya.*; Tanaka, Momoko; Tamotsu, Satoshi*; Hasegawa, Noboru; Nishikino, Masaharu; Pikuz, T.; Kaihori, Takeshi*; Kawachi, Tetsuya

Applied Physics A, 110(1), p.179 - 188, 2013/01

 Times Cited Count:23 Percentile:24.45(Materials Science, Multidisciplinary)

Journal Articles

Experimental verification of femtosecond laser ablation schemes by time-resolved soft X-ray reflective imaging

Tomita, Takuro*; Yamamoto, Minoru*; Hasegawa, Noboru; Terakawa, Kota*; Minami, Yasuo*; Nishikino, Masaharu; Ishino, Masahiko; Kaihori, Takeshi*; Ochi, Yoshihiro; Kawachi, Tetsuya; et al.

Optics Express (Internet), 20(28), p.29329 - 29337, 2012/12

 Times Cited Count:18 Percentile:28.31(Optics)

Pump and probe reflective imaging using a soft X-ray laser probe was applied to the observation of the early stage of femtosecond laser ablation process on platinum. In strongly excited area, drastic and fast reflectivity drop was observed. In moderately excited area, the decay of the reflectivity is slower than that in the strongly excited area, and the reflectivity reaches its minimum at t = 160 ps. In weakly excited area, laser-induced reflectivity change was not observed. These results give the critical information about the femtosecond laser ablation.

Journal Articles

Interaction of soft X-ray laser pulse radiation with aluminum surface; Nano-meter size surface modification

Ishino, Masahiko; Faenov, A.*; Tanaka, Momoko; Hasegawa, Noboru; Nishikino, Masaharu; Tamotsu, Satoshi*; Pikuz, S.*; Inogamov, N. A.*; Zhakhovsky, V. V.*; Skobelev, I.*; et al.

AIP Conference Proceedings 1465, p.236 - 240, 2012/07

 Times Cited Count:2 Percentile:30.79

We irradiated the focusing soft X-ray laser pulses having a wavelength of 13.9 nm and the duration of 7 ps to aluminum surface. After the irradiation process, the irradiated surface was observed with a scanning electron microscope. The surface modifications caused by soft X-ray laser single pulse exposure were clearly seen. In addition, it was found that the conical structures having around 100 nm in diameters were formed in the shallow features. The nano-meter size modified surface structures on aluminum induced by the soft X-ray laser pulse is interesting as the newly surface structure. Hence, the soft X-ray laser beam would be a candidate for a tool of micromachining. We also provide a thermomechanical modeling of the soft X-ray laser interaction with aluminum briefly to explain the surface modification.

Journal Articles

Development of single shot soft X-ray contact microscopy system for nano-scale dynamics measurement of living biological specimen

Kishimoto, Maki; Kado, Masataka; Ishino, Masahiko; Tamotsu, Satoshi*; Yasuda, Keiko*; Shinohara, Kunio*

AIP Conference Proceedings 1465, p.43 - 47, 2012/07

 Times Cited Count:5 Percentile:14.62

We have been developing a picosecond single shot soft X-ray contact microscopy system for observing the nanometer-scale inner structure of the living biological specimen in a hydrated condition. The microscopy system consists of an intense IR pump laser system for generating soft X-rays and X-ray microscope chamber. The pump laser system employs OPCPA technique to generate water-window X-rays effectively. The X-ray microscope chamber is composed of a vacuum chamber, a focusing lens, a metal film target, an in-vacuum type sample holder. The soft X-rays from the laser-induced plasma generated by pump laser pulse illuminates bio-specimens on the PMMA photo resist set in the in-vacuum sample holder. The photo resist is developed and the X-ray transmission imageis read out by AFM. We took X-ray images of hydrated Leydig cells from mouse testicle and demonstrated that the developed X-ray microscopy system has a spatial resolution of about 100 nm.

Journal Articles

Observation of organelle by a laser plasma X-ray microscope

Kado, Masataka; Kishimoto, Maki; Ishino, Masahiko; Tamotsu, Satoshi*; Yasuda, Keiko*; Shinohara, Kunio*

AIP Conference Proceedings 1465, p.246 - 250, 2012/07

 Times Cited Count:4 Percentile:14.62

Contact X-ray microscopy has a potential to image wet biological specimens in natural condition. It is very important to identify obtained features in the X-ray images, since X-ray microscopes have potential to image features that have not been visualized yet. We have proposed to compare the X-ray images of the biological specimens with the fluorescence images and to identify the features found in the X-ray images based on the features found in the fluorescence images. Comparing the X-ray images to the fluorescence images of the set biological cells, fine structures of the mitochondria in the X-ray images have been able to be identified.

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