Browsing by Author "Yamanoi K"
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- ItemEffect of Substrate and Thickness on the Photoconductivity of Nanoparticle Titanium Dioxide Thin Film Vacuum Ultraviolet Photoconductive Detector(MDPI (Basel, Switzerland), 2022-01) Cadatal-Raduban M; Kato T; Horiuchi Y; Olejníček J; Kohout M; Yamanoi K; Ono S; Selim F; Wang YVacuum ultraviolet radiation (VUV, from 100 nm to 200 nm wavelength) is indispensable in many applications, but its detection is still challenging. We report the development of a VUV photoconductive detector, based on titanium dioxide (TiO2) nanoparticle thin films. The effect of crystallinity, optical quality, and crystallite size due to film thickness (80 nm, 500 nm, 1000 nm) and type of substrate (silicon Si, quartz SiO2, soda lime glass SLG) was investigated to explore ways of enhancing the photoconductivity of the detector. The TiO2 film deposited on SiO2 substrate with a film thickness of 80 nm exhibited the best photoconductivity, with a photocurrent of 5.35 milli-Amperes and a photosensitivity of 99.99% for a bias voltage of 70 V. The wavelength response of the detector can be adjusted by changing the thickness of the film as the cut-off shifts to a longer wavelength, as the film becomes thicker. The response time of the TiO2 detector is about 5.8 μs and is comparable to the 5.4 μs response time of a diamond UV sensor. The development of the TiO2 nanoparticle thin film detector is expected to contribute to the enhancement of the use of VUV radiation in an increasing number of important technological and scientific applications.
- ItemElastic Scattering Time–Gated Multi–Static Lidar Scheme for Mapping and Identifying Contaminated Atmospheric Droplets(MDPI (Basel, Switzerland), 2023-01) Mui LV; Hung TN; Shinohara K; Yamanoi K; Shimizu T; Sarukura N; Shimadera H; Kondo A; Sumimura Y; Hai BV; Nguyen DV; Minh PH; Trung DV; Cadatal-Raduban M; Minamikawa TNumerical simulations are performed to determine the angular dependence of the MIe scattering cross-section intensities of pure water droplets and pollutants such as contaminated water droplets and black carbon as a function of the wavelength of the incident laser light, complex refractive index, and size of the scatterer. Our results show distinct scattering features when varying the various scattering parameters, thereby allowing the identification of the scattering particle with specific application to the identification of atmospheric pollutants including black carbon. Regardless of the type of scatterer, the scattering intensity is nearly uniform with a slight preference for forward scattering when the size of the particle is within 20% of the incident laser’s wavelength. The scattering patterns start to exhibit distinguishable features when the size parameter equals 1.77, corresponding to an incident laser wavelength of 0.355 μm and a particle radius of 0.1 μm. The patterns then become increasingly unique as the size parameter increases. Based on these calculations, we propose a time-gated lidar scheme consisting of multiple detectors that can rotate through a telescopic angle and be placed equidistantly around the scattering particles to collect the backscattered light and a commercially available Q-switched laser system emitting at tunable laser wavelengths. By using a pulsed laser with 10-ns pulse duration, our scheme could distinguish scattering centers that are at least 3 m apart. Our scheme called MIe Scattering Time-gated multi-Static LIDAR (MISTS–LIDAR) would be capable of identifying the type of atmospheric pollutant and mapping its location with a spatial resolution of a few meters.
- ItemFabrication of disk-shaped, deuterated resorcinol/formaldehyde foam target for laser–plasma experiments(Cambridge University Press in association with Chinese Laser Press, 2021-06-15) Kaneyasu Y; Nagai K; Cadatal-Raduban M; Golovin D; Shokita S; Yogo A; Jitsuno T; Norimatsu T; Yamanoi KResorcinol/formaldehyde (RF) foam resin is an attractive material as a low-density target in high-power laser–plasma experiments because of its fine network structure, transparency in the visible region, and low-Z element (hydrogen, carbon, and oxygen) composition. In this study, we developed disk-shaped RF foam and deuterated RF foam targets with 40–200 µm thickness and approximately 100 mg/cm3 density having a network structure from 100 nm to a few micrometers cell size. By deuteration, the polymerization rate was drastically slowed down owing to kinetic isotope effects. These targets were used in high-power laser experiments where a megaelectronvolt proton beam was successfully generated.
- ItemFabrication of high-concentration Cu-doped deuterated targets for fast ignition experiments(IOP Publishing Ltd on behalf of the International Atomic Energy Agency (IAEA), 2023-01) Ikeda T; Kaneyasu Y; Hosokawa H; Shigemori K; Norimastu T; Cadatal-Raduban M; Nagai K; Kojima S; Abe Y; Miura E; Kitagawa Y; Takemura M; Wang Y; Dun J; Guo S; Asano S; Takizawa R; Fujioka S; Shiraga H; Arikawa Y; Ozaki T; Iwamoto A; Sakagami H; Sawada H; Mori Y; Yamanoi KIn high-energy-density physics, including inertial fusion energy using high-power lasers, doping tracer atoms and deuteration of target materials play an important role in diagnosis. For example, a low-concentration Cu dopant acts as an x-ray source for electron temperature detection while a deuterium dopant acts as a neutron source for fusion reaction detection. However, the simultaneous achievement of Cu doping, a deuterated polymer, mechanical toughness and chemical robustness during the fabrication process is not so simple. In this study, we report the successful fabrication of a Cu-doped deuterated target. The obtained samples were characterized by inductively coupled plasma optical emission spectrometry, differential scanning calorimetry and Fourier transform infrared spectroscopy. Simultaneous measurements of Cu K-shell x-ray emission and beam fusion neutrons were demonstrated using a petawatt laser at Osaka University.
- ItemThe influence of CeF3 on radiation hardness and luminescence properties of Gd2O3-B2O3 glass scintillator(Springer Nature Limited, 2022-06-30) Kaewnuam E; Wantana N; Ruangtaweep Y; Cadatal-Raduban M; Yamanoi K; Kim HJ; Kidkhunthod P; Kaewkhao JThe effect of CeF3 concentration and γ-irradiation on the physical, optical and luminescence properties of Gd2O3-B2O3-CeF3 glasses were studied in this work. Before irradiation, the addition of CeF3 in glass degraded the network connectivity observed from FTIR and possibly created the non-bridging oxygen (NBO) in glass structure. This NBO caused the reduction of Ce3+/Ce4+ ratio in XANES, the red-shift in transmission spectra and the raise of refractive index with addition of CeF3 content. Such red-shift also was influenced by 4f-5d transition of Ce3+ dopant. This ion generated the strongest photoluminescence (PL) and radioluminescence (RL) in 0.3 mol% CeF3-doped glass with nanoseconds decay time. The irradiation with γ-rays damaged the glass structure, broke the chemical bonds, and created color center in the glass network. The non-bridging oxygen hole center (NBOHC), that absorbed photons in the visible light region, caused the darkening, color change and increment of refractive index. These irradiation effects on glass were mitigated by the addition of CeF3 that the electron donation of Ce3+ decreased the number of NBOHC. The Ce3+/Ce4+ ratio in most glasses after irradiation then reduced compared to them before irradiation, resulting to the decrease in PL and RL intensity. Our results confirm that CeF3 can enhance the radiation hardness of glass and the 0.3 mol% CeF3-doped glass is a promising glass scintillator.
- ItemUltrafast UV Luminescence of ZnO Films: Sub-30 ps Decay Time with Suppressed Visible Component(Wiley-VCH GmbH, 2024-05-10) Cadatal-Raduban M; Olejníček J; Hibino K; Maruyama Y; Písaříková A; Shinohara K; Asaka T; Lebedová Volfová L; Kohout M; Jiaqi Z; Akabe Y; Nakajima M; Harrison JA; Hippler R; Sarukura N; Ono S; Hubička Z; Yamanoi KUltrafast sub-100 picosecond luminescence is vital in many applications involving ultrafast events and time-of-flight systems. Materials exhibiting fast luminescence, such as barium fluoride (BaF2) and zinc oxide (ZnO), also suffer from an intrinsically slow nanosecond (ns) to microsecond (µs) luminescence. Here, 2.2 micrometer (µm)- to 5.7 µm-thick undoped ZnO films on soda-lime glass (SLG) substrates without a buffer layer by a hybrid pulsed reactive magnetron sputtering operating in the medium-frequency range (MF magnetron) assisted by an electron cyclotron wave resonance (ECWR) plasma is deposited. The undoped ZnO films exhibited superior optical properties characterized by intense ultraviolet (UV) luminescence, unprecedented ultrafast decay times, and for the case of MF+ECWR-deposited films, suppressed defect-related visible luminescence. The 2.2 µm-thick MF-deposited film exhibited the fastest 9-ps decay time at room temperature. The impressive properties of the films are attributed to the use of advanced deposition technology with properly tuned plasma parameters, especially a high degree of dissociation of molecular oxygen together with an increased proportion of activated zinc particles, leading to a higher deposition rate, better crystallinity, fewer defects, and a lower proportion of oxygen vacancies. These films will pave the way toward the development of time-of-flight detectors, high-resolution nuclear imaging cameras, and high-rate ultrafast timing devices.
