Kohei Sakai

Response Time-Shortened Zinc Oxide Scintillator for Accurate Single-Shot Synchronization of Extreme Ultraviolet Free-Electron Laser and Short-Pulse Laser

We report an over one-order-of magnitude improvement in the response time of conventional hydrothermal method-grown zinc oxide (ZnO) scintillator by introducing additional quenching channels via intentional indium ion doping. A 3-ps fluorescence decay time constant is achieved, therefore making it the fastest scintillator operating below 100 nm to date. Using this indium-doped ZnO, relative jitter between extreme ultraviolet free electron laser (EUV-FEL) probe and optical pump pulses is evaluated to be less than 3 ps. Moreover, pulses from these sources can be synchronized with 3-ps accuracy through in-situ observation of relative time difference in single-shot base.

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.

Fabrication of In-Doped ZnO Scintillator Mounted on a Vacuum Flange

High quality In-doped ZnO single crystal was grown using the hydrothermal method. The growth rate for both <;0001>; and <;000-1>; directions is about 80 μm/day. The X-ray rocking curve (XRC) full width at half maximum (FWHM) of the (0002) reflection is 24.2 arcsec. In order to make it possible to use this material as a scintillator for in situ imaging of soft X-ray laser with high spatial resolution, we prepared an In-doped ZnO wafer (9.0 mm x 9.0 mm x 0.75 mm) and mounted it on a vacuum flange. The decay time constant is evaluated to be 120 ps, therefore making it an ideal scintillator for in situ imaging device of soft X-ray laser with high spatial resolution. Furthermore, In-doped ZnO scintillator with such short decay time constant is suitable for high accuracy alignment and synchronization of ultrafast, short wavelength laser sources for pump-and-probe experiments.

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.

Indium-Doped ZnO Scintillator With 3-Ps Response Time for Accurate Synchronization of Optical and X-Ray Free Electron Laser Pulses

Accurate synchronization of pulses from an extreme ultraviolet free electron laser (EUV-FEL) and optical pulses from a Ti:sapphire laser is demonstrated. By using an indium (In)-doped zinc oxide (ZnO) crystal, pulses from these sources can be synchronized with ~ 3 -ps accuracy, an improvement of over three orders of magnitude compared to the widely-used cerium-doped yttrium aluminum garnet (Ce:YAG) scintillator. This dramatic improvement in response time will be valuable for pump-probe experiments using FEL and other ultrafast sources, and is expected to create new possibilities for time-resolved short wavelength spectroscopy.

Note: Light output enhanced fast response and low afterglow 6Li glass scintillator as potential down-scattered neutron diagnostics for inertial confinement fusion.

The characteristics of an APLF80+3Ce scintillator are presented. Its sufficiently fast decay profile, low afterglow, and an improved light output compared to the recently developed APLF80+3Pr, were experimentally demonstrated. This scintillator material holds promise for applications in neutron imaging diagnostics at the energy regions of 0.27 MeV of DD fusion down-scattered neutron peak at the worlds largest inertial confinement fusion facilities such as the National Ignition Facility and the Laser Mégajoule.

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.

Fast-Response and Low-Afterglow Cerium-Doped Lithium 6 Fluoro-Oxide Glass Scintillator for Laser Fusion-Originated Down-Scattered Neutron Detection

Scintillation properties of Ce3+-doped 20Al(PO3)3-80LiF glasses were investigated in order to seek a candidate for down-scattered neutron scintillator in nuclear fusion diagnostics. The decay constant of APLF80 + 3Ce with 5.5 MeV alpha particles from 241Am radioisotope excitation was measured to be 32.1 ns. Moreover, sufficiently low afterglow decay profile and improved light output of APLF80 + 3Ce were experimentally demonstrated.

Fast Fe-Doped ZnO Scintillator for Accurate Synchronization of Femtosecond Pulses from XFEL and Conventional Ultrafast Laser

The luminescence rise time of a Fe-doped ZnO X-ray scintillator was measured to be less than 4 ps. This allows timing control between XFEL pulses and femtosecond lasers to within a few picosecond accuracy.