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Nakanishi, Ryuzo; Oba, Hironori; Saeki, Morihisa; Wakaida, Ikuo; Tanabe, Rie*; Ito, Yoshiro*
Optics Express (Internet), 29(4), p.5205 - 5212, 2021/02
Times Cited Count：13 Percentile：83.13(Optics)Laser-induced breakdown spectroscopy (LIBS) combined with liquid jets was applied to the detection of trace sodium (Na) in aqueous solutions. The sensitivities of two types of liquid jets were compared: a liquid cylindrical jet with a diameter of 500 
m and a liquid sheet jet with a thickness of 20 m. Compared with the cylindrical jet, the liquid sheet jet effectively reduced the splash from the laser-irradiated surface and produced long-lived luminous plasma. The limit of detection (LOD) of Na was determined to be 0.57 g/L for the sheet jet and 10.5 g/L for the cylindrical jet. The LOD obtained for the sheet jet was comparable to those obtained for commercially available inductively coupled plasma emission spectrometers.
O
ceramic thin diskMaruyama, Momoko; Okada, Hajime; Ochi, Yoshihiro; Nagashima, Keisuke
Optics Express (Internet), 24(2), p.1685 - 1692, 2016/01
Times Cited Count：5 Percentile：30.58(Optics)We have developed a 1 kHz regenerative amplifier using an Yb:YO ceramic thin disk as the gain medium. Furthermore, the thermal conductivity and heat generation property of Yb: YO ceramic were investigated. In the developed regenerative amplifier, a laser beam is bounced off the thin disk six times in each round trip. The output energy is over 2 mJ, spectral bandwidth is 1.8 nm at FWHM, and pulse duration after pulse compression is 0.9 ps.
Oks, E.*; Dalimier, E.*; Faenov, A.*; Pikuz, T.*; Fukuda, Yuji; Andreev, A.*; Koga, J. K.; Sakaki, Hironao; Kotaki, Hideyuki; Pirozhkov, A. S.; et al.
Optics Express (Internet), 23(25), p.31991 - 32005, 2015/12
Times Cited Count：7 Percentile：38.91(Optics)We present experiments dealing with a femtosecond laser-driven cluster-based plasma, where by analyzing the nonlinear phenomenon of satellites of spectral lines of Ar XVII, we revealed the nonlinear phenomenon of the generation of the second harmonic of the laser frequency. For performing this analysis we developed new results in the theory of satellites of spectral lines. From such lineshape analysis we found, in particular, that the efficiency of converting the short (40 fs) intense (3
10
W/cm
) incident laser light into the second harmonic was 2%. This result is in the excellent agreement with the 2-Dimensional Particle-In-Cell (2D PIC) simulation that we also performed. There is also an order of magnitude agreement between the thresholds for the SHG found from the line shape analysis and from the 2D PIC simulations.
Ochi, Yoshihiro; Nagashima, Keisuke; Maruyama, Momoko; Tsubouchi, Masaaki; Yoshida, Fumiko; Kono, Nanase; Mori, Michiaki; Sugiyama, Akira
Optics Express (Internet), 23(11), p.15057 - 15064, 2015/06
Times Cited Count：25 Percentile：78.65(Optics)We have developed a 1 kHz repetition picosecond laser system dedicated for intense terahertz (THz) pulse generation. The system comprises a chirped pulse amplification laser equipped with a Yb:YAG thin-disk amplifier. At room temperature, the Yb:YAG thin-disk regenerative amplifier provides pulses having energy of over 10 mJ and spectral bandwidth of 1.2 nm. The pulse duration achieved after passage through a diffraction grating pair compressor was 1.3 ps. By employing this picosecond laser as a pump source, THz pulses having a peak frequency of 0.3 THz and 4 J of energy were generated by means of optical rectification in an Mg-doped LiNbO crystal.
Itakura, Ryuji; Kumada, Takayuki; Nakano, Motoyoshi*; Akagi, Hiroshi
Optics Express (Internet), 23(9), p.10914 - 10924, 2015/05
Times Cited Count：16 Percentile：65.37(Optics)We propose and experimentally demonstrate a method for characterizing vacuum ultraviolet (VUV) pulses based on time-resolved reflection spectroscopy of fused silica pumped by an intense laser pulse. Plasma mirror reflection is used as an ultrafast optical switch, which enables us to measure frequency-resolved optical gating (FROG) traces. The VUV temporal waveform can be retrieved from the measured FROG trace using principal component generalized projections algorithm with modification. The temporal profile of the plasma mirror reflectivity is also extracted simultaneously.
Oba, Hironori; Saeki, Morihisa; Wakaida, Ikuo; Tanabe, Rie*; Ito, Yoshiro*
Optics Express (Internet), 22(20), p.24478 - 24490, 2014/10
Times Cited Count：17 Percentile：66.56(Optics)For aqueous-solution-based elemental analysis, we used a thin liquid sheet (m-scale thickness) in laser-induced breakdown spectroscopy with nanosecond laser pulses. Laser-induced plasma is emitted by focusing a pulsed Nd:YAG laser (1064 nm) on a 5- to 80-m-thick liquid sheet in air. To optimize the conditions for detecting elements, we studied how the signal-to-background ratio (SBR) for H
Balmer and Na-neutral emission lines depends on the liquid-sheet thickness. The SBR of the H Balmer and Na-neutral lines was maximized for a sheet thickness of 
20 m at the laser energy of 100 mJ. The hydrodynamics of liquid flow induced by the laser pulse was analyzed by laser flash shadowgraph imaging. Time-resolved observation of the hydrodynamics and plasma emission suggests that the dependence of the SBR on the liquid-sheet thickness is correlated with the volume of flowing liquid that interacts with the laser pulses.
Kondo, Masato*; Tsubouchi, Masaaki
Optics Express (Internet), 22(12), p.14135 - 14147, 2014/06
Times Cited Count：18 Percentile：66.56(Optics)We investigated liquid-sheet jets with controllable thickness for application to terahertz (THz) spectroscopy. Slit-type and colliding-jet nozzles were used to generate optically flat liquid jets. The thickness of the liquid sheet was determined precisely by spectral interference and THz time-domain-spectroscopy methods. By adjusting the collision angle of the colliding-jet nozzle, we could control the thickness of the liquid sheet from 50 to 120 m.
-raysKosuge, Atsushi; Mori, Michiaki; Okada, Hajime; Hajima, Ryoichi; Nagashima, Keisuke
Optics Express (Internet), 22(6), p.6613 - 6619, 2014/03
Times Cited Count：2 Percentile：13.46(Optics)Nowadays, generation of energy-tunable, monochromatic -rays is needed to establish a nondestructive assay method of nuclear fuel materials. The -rays are generated by collision of laser photons stored in a cavity and relativistic electrons. We propose a configuration of an enhancement cavity capable of performing polarization control fabricated by a combination of a four-mirror ring cavity with a small spot inside a cavity and a three-mirror of reflective optics as an image inverter for polarization-selectable -rays. The image inverter introduces a phase shift of specific polarization which can be used to generate an error signal to lock an optical cavity at a resonance condition.
Yogo, Akifumi; Kondo, Kiminori; Mori, Michiaki; Kiriyama, Hiromitsu; Ogura, Koichi; Shimomura, Takuya; Inoue, Norihiro*; Fukuda, Yuji; Sakaki, Hironao; Jinno, Satoshi; et al.
Optics Express (Internet), 22(2), p.2060 - 2069, 2014/01
Times Cited Count：10 Percentile：49.33(Optics)Khumaeni, A.; Tampo, Motonobu; Akaoka, Katsuaki; Miyabe, Masabumi; Wakaida, Ikuo
Optics Express (Internet), 21(24), p.29755 - 29768, 2013/12
Times Cited Count：51 Percentile：91.11(Optics)Intensified microwave coupled by a loop antenna (diameter of 3 mm) has been employed to enhance the laser-induced breakdown spectroscopy (LIBS) emission. In this method, a laser plasma was induced on GdO sample at a reduced pressure by focusing a pulsed Nd:YAG laser (532 nm, 10 ns, 5 mJ) at a local point, at which electromagnetic field was produced by introducing microwave radiation using loop antenna. The plasma emission was significantly enhanced by absorbing the microwave radiation, resulting in high-temperature plasma and long-lifetime plasma emission. By using this method, the enhancement of Gd lines was up to 32 times, depending upon the emission lines observed. A linear calibration curve of Ca contained in the GdO sample was made. The detection limit of Ca was approximately 2 mg/kg. This present method is very useful for identification of trace elements in nuclear fuel and radioactive materials.
Daido, Hiroyuki; Suzuki, Yoji; Kawachi, Tetsuya; Fukuda, Takeshi*; Nakagiri, Toshio; Kaku, Masanori*; Kubodera, Masakazu*
Optics Express (Internet), 21(23), p.28182 - 28188, 2013/11
Times Cited Count：1 Percentile：7.09(Optics)We describe the direct measurement of actual transmittance of sodium samples with thickness of a 2 mm and 3 mm in a spectral range 
115 nm, resulting in 50% transmittance of 3 mm thick solid and liquid sodium samples including transmission of a pair of the windows at the wavelength of 120 nm, giving an extinction coefficient of 10
to 10
which represents the sodium with a few cm thickness to be partially transparent for this wavelength. To confirm the measurement, we perform simple imaging experiments by the ultra-violet light passing through a 8 mm-thick sodium sample to illuminate a mesh as an object, resulting in obtaining a clear image.
clusters formed in a supersonic expansion of a gas mixtureJinno, Satoshi; Fukuda, Yuji; Sakaki, Hironao; Yogo, Akifumi; Kanasaki, Masato; Kondo, Kiminori; Faenov, A. Ya.*; Skobelev, I. Yu.*; Pikuz, T.; Boldarev, A. S.*; et al.
Optics Express (Internet), 21(18), p.20656 - 20674, 2013/09
Times Cited Count：22 Percentile：73.17(Optics)A detailed mathematical model is presented for a submicron-sized cluster formation in a binary gas mixture flowing through a three-staged conical nozzle. In order to experimentally confirm this model, the cluster sizes have been evaluated using the Mie scattering method, which is to measure the angular distribution of light scattered from targets. The mean sizes of CO clusters produced in the gas mixtures of CO(30%)/H(70%) and CO(10%)/He(90%) are estimated to be 0.28
0.03 m and 0.260.04 m, respectively. In addition, total gas density profiles measured with an interferometer were found to be agreed with the numerical modeling within a factor of two. The dryness (
ratio) in the targets was found to support the numerical modeling. Thus, our mathematical model of cluster formation was proved to be reliable enough for the binary gas mixture by the experimental results.
Nagashima, Keisuke; Kosuge, Atsushi; Ochi, Yoshihiro; Tanaka, Momoko
Optics Express (Internet), 21(16), p.18640 - 18645, 2013/07
Times Cited Count：14 Percentile：59.39(Optics)A novel method for increasing diffraction efficiency of transmission gratings is proposed. In this method, dielectric multilayers are inserted between a grating region and a substrate. These multilayers work as an anti-reflection coating for the transmission grating. It is presented that a grating with 1740 grooves/mm has the diffraction efficiency over 99% using this anti-reflection coating.
Tsubouchi, Masaaki; Kumada, Takayuki
Optics Express (Internet), 20(27), p.28500 - 28506, 2012/12
Times Cited Count：5 Percentile：28.04(Optics)A high-efficiency etalon operated in the terahertz (THz) frequency region has been proposed to generate a THz pulse train. To achieve high-conversion efficiency to the pulse train, an optical shutter is employed in this etalon. The etalon is composed of a silicon (Si) plate as an input coupler and an indium-tin-oxide (ITO)-coated glass plate as an output coupler. After THz light is introduced into the etalon through the Si plate, the optical shutter pulse irradiates the Si surface to generate a photoconductive layer that acts as a highly reflective mirror for THz light. A THz pulse train and its comb-shaped spectrum have been realized by the use of the proposed etalon with the optical shutter. A finesse F of 9.04 was achieved at the spectral range of 75 GHz in this etalon.
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：19 Percentile：64.97(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.
Iwayama, Hiroshi*; Nagasono, Mitsuru*; Harries, J.; Shigemasa, Eiji*
Optics Express (Internet), 20(21), p.23174 - 23179, 2012/10
Times Cited Count：15 Percentile：59.41(Optics)Ikeda, Shiro*; Kono, Hidetoshi
Optics Express (Internet), 20(4), p.3375 - 3387, 2012/02
Times Cited Count：10 Percentile：46.91(Optics)Pikuz, T.; Faenov, A.*; Fukuda, Yuji; Kando, Masaki; Bolton, P.; Mitorfanov, A.*; Vinogradov, A.*; Nagasono, Mitsuru*; Ohashi, Haruhiko*; Yabashi, Makina*; et al.
Optics Express (Internet), 20(4), p.3424 - 3433, 2012/02
Times Cited Count：27 Percentile：76.85(Optics)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：19 Percentile：66.78(Optics)
line emission from Mo and Ag plate were experimentally studied by using ultra-high intensity, clean femtosecond laser pulses. Absolutely yield of 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 yields were obtained for both Mo and Ag with higher contrast ratios and high irradiance. The conversion efficiencies of 4.28 10
/sr for Mo and 4.84 10/sr for Ag, the highest values ever obtained, have been demonstarted with the contrast ratio of 10
to 10
.
Togashi, Tadashi*; Takahashi, Eiji*; Midorikawa, Katsumi*; Aoyama, Makoto; Yamakawa, Koichi; Sato, Takahiro*; Iwasaki, Atsushi*; Owada, Shigeki*; Okino, Tomoya*; Yamanouchi, Kaoru*; et al.
Optics Express (Internet), 19(1), p.317 - 324, 2011/01
Times Cited Count：96 Percentile：96.45(Optics)The 13th harmonic of a Ti:sapphire (Ti:S) laser in the plateau region was injected as a seeding source to a 250-MeV free-electron-laser (FEL) amplifier. When the amplification conditions were fulfilled, strong enhancement of the radiation intensity by a factor of 650 was observed. The random and uncontrollable spikes, which appeared in the spectra of the Self-Amplified Spontaneous Emission (SASE) based FEL radiation without the seeding source, were found to be suppressed drastically to form to a narrow-band, single peak profile at 61.2 nm. The properties of the seeded FEL radiation were well reproduced by numerical simulations. We discuss the future precept of the seeded FEL scheme to the shorter wavelength region.
