Ryosuke Nishi

Potential High-Spatial Resolution In-Situ Imaging of Soft X-Ray Laser Pulses With ZnO Crystal

We show that a hydrothermal method-grown ZnO is a potential material of an imaging device for soft X-ray laser diagnostics. The beam profile of a soft X-ray laser was evaluated by characterizing the exciton emission patterns of ZnO. The single shot image of emission patterns is clear enough to monitor the evolution of the beam radius around the focal point. By plotting the emission pattern radii at each position, the beam profile of the Ni-like Ag ion plasma laser was estimated from the waist radii as 29 μm and 21 μm in the horizontal and vertical axis, respectively. The divergence angle was estimated to be around 7.2 mrad and 11 mrad in the horizontal and vertical axis, respectively. The beam quality evaluated from the M2 factor was 47 along the horizontal axis and 50 along the vertical axis. Spatial resolution of the magnifier was estimated to be 6 μm and is expected to improve by optimizing the optics of the magnifier and using a telescope. Our results would enhance the use of ZnO as a high-spatial resolution in-situ imaging device that would play a crucial role in the development and application of soft X-ray light sources.

Evaluation of Soft X-ray Laser with In situ Imaging Device of High Spatial Resolution ZnO Scintillator

We demonstrate the potential of a hydrothermal method-grown ZnO as a high-spatial resolution imaging device for in-situ soft X-ray laser diagnostics by characterizing the exciton emission patterns. By plotting the emission pattern radii at each position, we estimated the evolution of the beam radius around the focal point. The beam profile of the Ni-like Ag ion plasma laser was estimated from the waist radii as 29 and 21 ?m, the divergence angle as 7.2 and 11 mrad and the M2 factor as 47 and 50 in the horizontal- and vertical-axis, respectively. Spatial resolution of the magnifier was estimated to be 6 ?m and is expected to improve by optimizing the optics of the magnifier and using a telescope. Our results would enhance the use of ZnO as an imaging device that would play a crucial role in the development and application of soft X-ray light sources.

Vacuum Ultraviolet Fluorescence Spectroscopy of Nd3+:LaF3 Using Femtosecond Extreme Ultraviolet Free Electron Laser

Time-resolved vacuum ultraviolet (VUV) fluorescence was observed from a Czochralski method-grown Nd3+:LaF3 crystal excited by 61 nm femtosecond pulses from the extreme ultraviolet free-electron laser (EUV-FEL). The 172 nm fluorescence peak exhibited double exponential fluorescence decay with slow and fast decay components of 6.7 and 1.9 ns, respectively. The spectral profile is similar to those previously reported, but the double exponential nature has never been attained using conventional short-wavelength pulsed lasers. Our results demonstrate the importance of the EUV-FEL for short-wavelength spectroscopy, not just for rare-earth-doped fluorides but also for wide-band-gap semiconductors such as AlGaN.

Spatial Resolution Evaluation of ZnO Scintillator as an In-situ Imaging Device in EUV Region

We captured single shot images of ZnO emission patterns originating from excitation with the EUV laser at Japan Atomic Energy Agency (JAEA). The EUV laser was focused to a spot size of 1 μm on the ZnO crystal by a Fresnel Zone Plate (FZP). The FZP was shifted along the propagation direction of the EUV beam, essentially changing the spot size at the ZnO surface. The emission pattern was detected by a magnifier. The waist radii were determined from the fitting curve as 5.0 μm along the horizontal axis and 4.7 μm along the vertical axis. We also evaluated the spatial resolution of the magnifier, which consists of a Schwarzschild mirror, two lenses and a camera lens to be about 4 μm. These results suggest that the ZnO crystal has sub-micron spatial resolution when used as an in-situ imaging device for the diagnostics of EUV/X-ray sources.

Electronic states of trivalent praseodymium ion doped in 20Al(PO 3)3-80LiF glass

We investigate the photoluminescence (PL) and photoluminescence excitation (PLE) spectra of 20Al(PO3)3–80LiF+Pr glass (APLF+Pr) and Pr3+-doped LiCaAlF6 crystal (Pr:LiCAF) in order to determine the electronic states of Pr3+ in APLF glass host and to improve APLF+Pr scintillation properties. Ultraviolet (UV) emission bands at around 250 and 340 nm were observed from both materials and these can be ascribed to 4f5d→4f2 transitions in Pr3+. Emission at around 400 nm was also obtained and is principally attributed to 1S0→4f2 transition. Difference in the emission profiles of these two materials was found to be due to the extent of the 5d band and its position relative to the 1S0 state. Increasing the concentration of Pr3+ up to 2 mol % was found to improve UV emission ratio due to the faster cross-relaxation of 4f states. This could improve the quantum efficiency of APLF+Pr as a neutron scintillator for scattered-neutron diagnostics in laser fusion research.

Time-Resolved Pump and Probe Experiment for Wide-Gap Semiconductors Using Free Electron Laser and Synchronously-Operated Femtosecond Laser

Pump–probe technique is an important means of studying the structure and dynamics of a single protein molecule. X-ray free electron lasers (XFELs) such as the Linac Coherent Light Source (LCLS) and SPring-8 Angstrom Compact free electron Laser (SACLA) provide the Angstrom-wavelength, high-intensity femtosecond pulses needed for revealing the structure of a single protein molecule without crystallization and for observing atomic motion during a chemical reaction via pump–probe experiments. In this paper, we demonstrated X-ray pump–optical probe and optical pump–X-ray probe experiments, creating new possibilities for time-resolved EUV spectroscopy of solid targets including wide-gap semiconductors such as gallium nitride.