Browsing by Author "Shinohara K"

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    Elastic 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 T
    Numerical 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.
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    Ultrafast 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 K
    Ultrafast 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.