Tomohiro Aoto

Absolute Measurement of Baselines up to 403 m Using Heterodyne Temporal Coherence Interferometer with Optical Frequency Comb

A heterodyne interference system is developed for baseline measurement by using an acoustic optical modulator and an optical frequency comb stabilized by a rubidium atomic clock. Temporal coherence interference occurs at discrete spatial positions, when two pulse trains overlap. An optical delay of the interferometer with a piezoelectric transducer is created to determine the peak positions of the interference fringe patterns, and the absolute distance is obtained at a high resolution of several tens of nanometers. The experimental results at baseline distances up to 403.2 m show a high reproducibility of about 6 µm.

Inner-valence states of N2+ and the dissociation dynamics studied by threshold photoelectron spectroscopy and configuration interaction calculation

The N2(+) states lying in the ionization region of 26-45 eV and the dissociation dynamics are investigated by high-resolution threshold photoelectron spectroscopy and threshold photoelectron-photoion coincidence spectroscopy. The threshold photoelectron spectrum exhibits several broad bands as well as sharp peaks. The band features are assigned to the N2(+) states associated with the removal of an inner-valence electron, by a comparison with a configuration interaction calculation. In contrast, most of the sharp peaks on the threshold photoelectron spectrum are allocated to ionic Rydberg states converging to N2(2+). Dissociation products formed from the inner-valence N2(+) states are determined by threshold photoelectron-photoion coincidence spectroscopy. The dissociation dynamics of the inner-valence ionic states is discussed with reference to the potential energy curves calculated.

Dynamics of double photoionization near the Ar 2p threshold investigated by threshold electron?Auger electron coincidence spectroscopy

Threshold electron–Auger electron coincidence spectroscopy measurements were carried out near the Ar 2p thresholds. Such a method allows us, for the first time, to observe the threshold electron yields associated with the selected final states of the Ar2+ ion: 3p4(1D2), 3p4(1S0), 3p4(3P) resulting from the 2p hole Auger decay. All the spectra reveal strong PCI distortion. Comparison with calculations carried out in the framework of a quantum-mechanical PCI model allows us to clarify the mechanisms and the dynamics of threshold electron production. In the 3p4(1D2) and 3p4(1S0) channels, contribution to the threshold electron yield comes essentially from the PCI retardation of slow photoelectrons. In the 3p4(3P) final state channel, an additional process of valence multiplet decay of the 3p4(1D2)6d state plays a role at and below the L2, L3 thresholds.

Operation of a fast polarization-switching source at the Photon Factory

We have been developing a fast polarization-switching source for the vacuum ultraviolet and soft X-ray region at the B15-16 straight section of the 2.5-GeV Photon Factory (PF) storage ring. The source consists of two tandem APPLE-II-type elliptically polarizing undulators (EPUs), namely, U#16-1 and U#16-2, and a fast kicker system. The target frequency of polarization switching is 10 Hz. As the first step, we installed U#16-1 and five identical bump kickers in the PF ring in March 2008. Then, we constructed U#16-2 and installed it in August 2010. The orbit switching operation at 10 Hz, for user experiments, started in January 2012. We describe the details of the operation status of two EPUs and the fast local bump system in this report.

Fast polarization switching in the soft X-ray region at PF BL-16A

Recent development in fast polarization switching at the soft X-ray beamline, BL-16A in the Photon Factory is reported. Two APPLE-II type undulators installed in a tandem configuration enables us to achieve polarization switching between not only two opposite circular polarizations, but also the vertical and horizontal linear polarizations. An energy shift is observed during polarization switching due to a vertical modulation in the electron beam, which has been reduced by properly correcting the electron orbit.

Sub-natural linewidth spectroscopy on core-valence doubly ionized states of OCS

Core–valence doubly ionized states of OCS, which are produced by the Coster–Kronig transitions following the S 2s ionization, have been investigated by using threshold photoelectron-Auger electron coincidence spectroscopy. The sub-natural linewidth regime achieved with this coincidence method enables us to locate the core–valence OCS2+ states, while the corresponding structures are almost smeared out on the S 2s Auger spectrum measured with conventional Auger electron spectroscopy.

Threshold photoelectron spectroscopy on inner-valence ionic states of NO.

The NO(+) states lying in the ionization region of 20-40 eV have been investigated by high-resolution threshold photoelectron spectroscopy and a configuration interaction calculation. Substantial agreement between the structures on the present experimental and theoretical spectra in the 21-27 eV range enables us to assign the relevant inner-valence ionic states unambiguously. The dissociation products from the ion states are measured with threshold photoelectron-photoion coincidence spectroscopy, and the dissociation processes are discussed with reference to the potential energy curves calculated. Sharp peaks are observed in the ionization region of 27.5-35 eV, which are allocated to ionic Rydberg states converging to NO(2+).

Molecular orientation change during adsorption of NO and N2O on Ir(111) observed by real-time wavelength-dispersive x-ray absorption spectroscopy with polarization switching

The molecular orientation of NO and N2O during adsorption on Ir(111) is observed by combining the wavelength-dispersive x-ray absorption spectroscopy with 1 Hz switching between the vertical and horizontal linear polarizations. It is revealed that NO adsorbs keeping its molecular axis at ∼20° from surface normal. In contrast, N2O rapidly adsorbs up to 2/3 of the saturation coverage with an orientation angle of ∼35°, then turns to a slow adsorption phase with larger orientation angles, and gradually reaches its saturation with an average orientation angle of ∼45°. Such a complicated behavior is interpreted by assuming different adsorption sites.

Autoionization of the Ne+ Rydberg states formed via valence photoemission

Autoionization decay from Ne+ Rydberg states has been investigated by using multi-electron spectroscopy at a photon energy of 200.4 eV, where the autoionizing states have been produced through valence photoemission with simultaneous excitation into Rydberg orbitals. The coincidence measurements enable one to resolve individual autoionization lines corresponding to decays from the Ne+ 2p−2(1D)nl, 2p−2(1S)nl, 2s−12p−1(1,3P)nl and 2s−2(1S)nl Rydberg states. The present investigation revealed the autoionization decay features of the Rydberg states: branching ratios, which show strong selectivity towards the Ne2+ final states and asymmetric line shapes in the electron spectra, which have been analysed in terms of the interaction between the discrete state and each continuum. In addition, it is demonstrated that the autoionization decay feature of the Ne+ 2s−12p−1(1P)3p 2S state is characterized by a strong interaction with 2s−12p−1(3P)nl autoionizing states.

Autoionization selectivity of Ne+ Rydberg states converging to Ne2+(1Se)

Indirect double photoionization processes of Ne have been studied in the photon energy range from 65.5 to 68.3 eV by using a threshold-photoelectron−photoelectron coincidence method, where intermediately formed Ne+ states have been defined by the detection of threshold photoelectrons and fast electrons from their autoionizing decay have been analysed in coincidence. The present investigation revealed that each Ne+ Rydberg series converging to Ne2+(1Se) shows notable selectivity in the autoionizing decay to the final Ne2+ states.