大饗 千彰*; Harries, J.; 岩山 洋士*; 川口 健太郎*; 久間 晋*; 宮本 祐樹*; 永園 充*; 中嶋 享*; 中野 逸夫*; 繁政 英治*; et al.
Journal of the Physical Society of Japan, 85(3), p.034301_1 - 034301_10, 2016/03
Previous experimental studies of superradiance (SR) in multi-level systems have been explainable using the predictions of the well-known simple two-level SR model. However our recent study using EUV free-electron laser excitation of helium atoms, where SR was observed at wavelengths of 502 nm, 668 nm, and 728 nm, revealed behaviour which necessitates a full multi-level treatment of the SR development. In this paper, we report simulations of the initial excitation by the FEL pulses, and the subsequent development of multi-level SR. The results of the simulation reproduce the experimental findings, and reveal that competitive SR on two transitions with a common upper level plays an important role in the development of the system.
Harries, J.; 岩山 洋士*; 永園 充*; 富樫 格*; 矢橋 牧名*; 久間 晋*; 中嶋 享*; 宮本 祐樹*; 大饗 千彰*; 笹尾 登*; et al.
Journal of Physics B; Atomic, Molecular and Optical Physics, 48(10), p.105002_1 - 105002_9, 2015/05
We report the observation of superfluorescence at wavelengths (in air) of 501.6 nm, 667.8 nm, and 728.1 nm following the excitation of helium atoms with free-electron laser pulses at wavelengths of 53.7 nm (=3 excitation) and 52.2 nm (=4 excitation). The observed wavelengths of the superfluorescence pulses correspond to 1s3p-1s2s, 1s3d-1s2p, and 1s3s-2p transitions. Observation of superfluorescence on these transitions implies either competing cascade decays, or direct excitation of non-dipole allowed transitions. We have studied the time structure of the emitted pulses using a streak camera, and the results cannot be explained by straightforward considerations using the usual model for two-level superfluorescence.
中嶋 享*; Harries, J.; 岩山 洋士*; 久間 晋*; 宮本 祐樹*; 永園 充*; 大饗 千彰*; 富樫 格*; 矢橋 牧名*; 繁政 英治*; et al.
Journal of the Physical Society of Japan, 84(5), p.054301_1 - 054301_7, 2015/05
In this paper, we report the results of measurements of the intensities and delays of super-radiance decays from excited helium atoms at multiple wavelengths. The experiment was performed using extreme ultraviolet radiation produced by the free electron laser at the SPring-8 Compact SASE Source test accelerator facility as an excitation source. We observed superradiant transitions on the 1s3p1s2s (=502 nm), 1s3d1s2p (=668 nm), and 1s3s1s2p (=728 nm) transitions. The pulse energy of each transition and its delay time were measured as a function of the target helium gas density. Several interesting features of the data, some of which appear to contradict with the predictions of the simple two-level super-radiance theory, are pointed out.
岩山 洋士*; Harries, J.; 繁政 英治*
Physical Review A, 91(2), p.021402_1 - 021402_5, 2015/02
We present extreme-ultraviolet (EUV) fluorescence spectra of Ar clusters irradiated by intense EUV free-electron laser (FEL) pulses focused to intensities of up to 310 W/cm at a wavelength of 51 nm. The spectra reveal fluorescence at wavelengths shorter than that of the incident radiation, which can be assigned to EUV fluorescence lines from excited multiply-charged ions Ar with as high as 6. This demonstrates that charge states as high as 7+ are produced by the FEL irradiation. The cluster size and FEL power dependences of the spectral features suggest that an inhomogeneous distribution of charge within the clusters reduces ionization thresholds at the cluster surface.
寺岡 有殿; 神農 宗徹*; 高岡 毅*; Harries, J.; 岡田 隆太; 岩井 優太郎*; 吉越 章隆; 米田 忠弘*
電気学会論文誌,C, 134(4), p.524 - 525, 2014/04
Surface temperature dependence on the translational energy induced nitridation of Al(111) has been investigated by using synchrotron radiation photoemission spectroscopy. Incubation time for N1s photoemission onset was found to be longer at lower temperatures than 473 K, indicating precursor formation followed by proper nitridation. The major product is the three-fold N atom. The minor four-fold one decreased at higher temperatures. Three step reaction mechanisms, that is, translational energy induced nitridation, precursor formation, and proper nitridation of the precursor states, were presented.
寺岡 有殿; 戸出 真由美*; Harries, J.; 吉越 章隆
電気学会論文誌,C, 134(4), p.473 - 478, 2014/04
The desorption of deuterium molecules from a V(001) surface is limited by deuterium diffusion in the oxide layer. The distribution of desorption temperature can be controlled by varying the oxide layer thickness. The desorption of deuterium molecules existing near the surface shifts towards a higher temperature region over room temperature. The desorption of deuterium molecules dissolving in the bulk could not be controlled because the oxide layer is still degraded near the higher desorption temperature. Whether the deuterium desorption can be controlled by the oxide layer or not is determined by a relationship between oxide degradation temperatures and deuterium desorption temperatures.
Harries, J.; 岩山 洋士*; 沖原 理沙*; 永園 充*; 繁政 英治*
JPS Conference Proceedings (Internet), 1, p.013083_1 - 013083_6, 2014/03
In this article we describe four recent results from "photon-in, photon-out" fluorescence spectroscopy studies using the SPring-8 compact SASE source SCSS. Fluorescence spectroscopy avoids problems due to space charge, and is particularly suited to the highly-intense FEL pulses, since multiple excitations/ionisations occur for each laser shot.
繁政 英治*; 永園 充*; 岩山 洋士*; Harries, J.; 石川 理沙*
Journal of Physics B; Atomic, Molecular and Optical Physics, 46(16), p.164020_1 - 164020_5, 2013/08
Time-resolved extreme-ultraviolet (EUV) fluorescence spectroscopy has been applied to study the multi-photon, single ionization of Ne irradiated by intense EUV-free-electron laser (FEL) pulses at a wavelength of 51 nm. A broad, intense peak at a wavelength of around 46 nm is observed, which is shorter than the incident FEL wavelength. The time-dependence of the fluorescence reveals that the peak has two un-resolved components, which we attribute to the decay of the excited ion states Ne2s(S) and 2p(P)3s(P) at 46.0 nm and 44.6 nm. From the observed intensity ratios and fluorescence lifetimes we conclude that the Ne 2p (P)3s(P) state is populated by two-photon resonance-enhancement, via a 2p3p doubly-excited state of Ne.
Harries, J.; 永園 充*; 岩山 洋士*; 繁政 英治*
Journal of Physics B; Atomic, Molecular and Optical Physics, 46(16), p.164021_1 - 164021_5, 2013/08
Using the third harmonic of the FEL radiation from the SPring-8 compact SASE source SCSS we have studied the effects on SASE (self-amplified stimulated emission) pulses with central wavelengths near 20 nm due to passage through a helium gas cell. The positions of zero ionisation cross-section close to wavelengths corresponding to double-excitations allow operation as an efficient wavelength filter, with effectively 100% transmitted peak intensity until the Doppler-broadening limit is reached. We discuss how the time profile of the SASE pulses is affected, and discuss potential applications.
矢橋 牧名*; 田中 均*; 田中 隆次*; 冨澤 宏光*; 富樫 格*; 永園 充*; 石川 哲也*; Harries, J.; 彦坂 泰正*; 菱川 明栄*; et al.
Journal of Physics B; Atomic, Molecular and Optical Physics, 46(16), p.164001_1 - 164001_19, 2013/08
The concept, design, and performance of Japan's compact FEL facilities, the SPring-8 Compact SASE Source test accelerator (SCSS) and SPring-8 Angstrom Compact free electron LAser (SACLA), and their applications are reviewed. At SCSS, intense, ultrafast FEL pulses at extreme ultraviolet (EUV) wavelengths have been utilized for investigating various multiphoton processes in atoms, molecules and clusters by means of ion and electron spectroscopy. The quantum optical effect superfluorescence has been observed with EUV excitation. A pump-probe technique combining FEL pulses with near infrared laser pulses has been realized to study the ultrafast dynamics of atoms, molecules and clusters in the sub-picosecond regime. At SACLA, deep inner-shell multiphoton ionization by intense X-ray free-electron laser pulses has been investigated. The development of seeded FEL sources for producing transversely and temporally coherent light, as well as the expected impact on advanced science are discussed.
下條 竜夫*; 池上 剛史*; 本間 健二*; Harries, J.; 為則 雄祐*
Journal of Physics B; Atomic, Molecular and Optical Physics, 46(7), p.075102_1 - 075102_9, 2013/04
The novel spectroscopic technique of time-resolved fluorescence-photo-ion coincidence spectroscopy (TFPICO) has been applied to the investigation of the decay processes of 2p inner-shell excited Ar atoms and clusters. For the Ar atom, only that fluorescence accompanying the production of Ar showed a strong dependence on excitation energy. This dependence is discussed in terms of competing Auger decay processes. For Ar clusters, the TFPICO spectra for dimer ions (Ar) revealed long-lifetime fluorescence components which can be attributed to the "third excimer continuum". With this work we demonstrate the usefulness of this technique for investigating the decay processes of inner-shell excited atoms and clusters.
寺岡 有殿; 神農 宗徹*; Harries, J.; 吉越 章隆
Journal of Physics; Conference Series, 417, p.012031_1 - 012031_7, 2013/03
Aluminum can not react with N gas around 473 K, we found the direct nitridation of Al(111) surface at 473 K by using supersonic N molecular beam. We analyzed the thin film by using synchrotron radiation photoemission spectroscopy. At the surface temperature of 473 K, clear uptake of N-1s spectrum was observed depending on the N dose at the incident N energy of 2.0 eV. The N1s photoemission intensity increased almost linearly with increasing N dose. When surface temperature was 373 K, clear uptake of N1s spectrum was also observed at the incident N energy of 2.0 eV. In the case of surface temperature of 300 K, the N-1s photoemission peak was not observed until the N dose of 1.010 molecules/cm. Such large temperature dependence may be attributed to the N atom diffusion into bulk aluminum from the topmost surface because N atoms were observed even in a depth of 1 nm by angle resolved photoemission measurements.
寺岡 有殿; 井上 敬介*; 神農 宗徹*; Harries, J.; 岡田 隆太; 岩井 優太郎*; 高岡 毅*; 吉越 章隆; 米田 忠弘*
第56回日本学術会議材料工学連合講演会講演論文集, p.360 - 361, 2012/10
岩山 洋士*; 永園 充*; Harries, J.; 繁政 英治*
Optics Express (Internet), 20(21), p.23174 - 23179, 2012/10
Extreme ultraviolet (EUV) fluorescence emitted from Ar clusters irradiated by intense EUV free electron laser (FEL) pulses has been investigated. The EUV fluorescence spectra display rich structure at wavelengths shorter than the incident FEL wavelength of 51 nm. The results suggest that multiply-charged ions are produced following the ion-electron recombination processes which occur in the nanoplasma created by multi-photon excitation during the intense EUV-FEL pulses.
Harries, J.; 寺岡 有殿; 戸出 真由美; 吉越 章隆
Applied Physics Express, 5(3), p.031802_1 - 031802_3, 2012/03
Angle-resolved photoelectron spectroscopy is an established technique for obtaining information on the depth-dependence of the concentration of elements within a sample. When synchrotron radiation is used as the X-ray source, the high flux and high energy resolution allow chemical-state specific information to be obtained - an area where the technique has advantages over more quantitative techniques with higher depth resolution. Here we describe the application of the technique at the surface chemistry end-station at BL23SU, SPring-8, where thin films can be analysed in situ. The technique is applied to studying the natural oxide surface layer of VCrTi, a hydrogen-storage material.
永園 充*; Harries, J.; 岩山 洋士*; 富樫 格*; 登野 健介*; 矢橋 牧名*; 仙波 泰徳*; 大橋 治彦*; 石川 哲也*; 繁政 英治*
Physical Review Letters, 107(19), p.193603_1 - 193603_5, 2011/11
We have observed and characterized 501.6 nm collective spontaneous emission (superfluorescence) following 113 excitation of helium atoms by 53.7 nm free-electron laser radiation. Emitted pulse energies of up to 100 nJ (10 photons) are observed, corresponding to a photon number conversion efficiency of up to 10%. We observe the peak intensity to scale as , and the pulse width and delay with respect to the pump pulse to scale as , where is the atom number density. Emitted pulses as short as 1 ps are observed, which corresponds to a rate around 75000 times faster than the spontaneous 1312 decay rate. To our knowledge this is the first observation of superfluorescence following pumping in the extreme ultraviolet wavelength region, and extension of the technique to the generation of EUV and X-ray superfluorescence pulses should be straightforward by using suitable atomic systems and pump wavelengths.
寺岡 有殿; 井上 敬介*; 神農 宗徹*; Harries, J.; 吉越 章隆
第55回日本学術会議材料工学連合講演会講演論文集, p.236 - 237, 2011/10
原子力機構では、超音速分子線と高輝度・高分解能放射光を同時に試料表面に照射して、リアルタイムで表面をその場光電子分光観察する装置を開発し、SPring-8の専用軟X線ビームライン:BL23SUに設置した。質量分析器も併用すれば、表面の化学結合状態の変化と反応生成物の脱離収率を同時にモニタすることもできる。入射分子の運動エネルギーを反応制御パラメータとして、表面反応のダイナミクスにまで立ち入った反応機構の解明が期待できる。Si酸化では、900K以上の温度でO分子線と反応するSi(001)表面を光電子分光観察すると同時に、脱離するSiO分子の収率をモニタすることで、酸化膜形成とエッチングが同時に起こる一見奇妙な表面反応の機構を解明した。アルミニウムはNガスと反応しないが、N分子の運動エネルギーを2eVにまで高めたところ、表面温度が473Kで1nm程度の窒化膜が形成されることを見いだした。Ni酸化では酸素吸着曲線に見られるプラトーがO分子の運動エネルギーに大きく依存して消失することを見いだした。他にTi, Ru, Cuの酸化においてもO分子の運動エネルギー効果が見いだされた。
長岡 伸一*; 福沢 宏宣*; Prmper, G.*; 竹本 真唯*; 高橋 修*; 山口 拓洋*; 垣内 拓大*; 田林 清彦*; 鈴木 功*; Harries, J.; et al.
Journal of Physical Chemistry A, 115(32), p.8822 - 8831, 2011/07
In an aim to create a sharp molecular knife, we have studied site-specific fragmentation caused by Si:2p core photoionization of bridged trihalosilyl-trimethylsilyl molecules in the vapor phase. Highly site-specific bond-dissociation has been found to occur around the core-ionized Si site in some of the molecules studied. The site-specificity in fragmentation and the 2p binding-energy difference between the two Si sites depend in similar ways on the inter-site bridge and the electronegativities of the included halogen atoms. The present experimental and computational results show that for efficient cutting, the following conditions for the two atomic sites to be separated by the knife should be satisfied. First, the sites should be located far from each other and connected by a chain of saturated bonds so that inter-site electron migration can be reduced. Secondly, the chemical environments of the atomic sites should be as different as possible.
Harries, J.; 下條 竜夫*; 本間 健二*; 國分 美希*; Sullivan, J. P.*; Lebech, M.*; 東 善郎*
Journal of Physics B; Atomic, Molecular and Optical Physics, 44(9), p.095101_1 - 095101_7, 2011/05
We have studied the production of long-lived, highly-excited, neutral hydrogen atom fragments following oxygen 1s inner-shell excitation/ionization of gas-phase water molecules using synchrotron radiation. Striking differences to fragment ion and low- neutral H yields are observed close to threshold. To investigate the decay pathways involved the neutral fragments were also detected in coincidence with H, O, O, and OH fragments.