Abstract We investigated the laser performance of ytterbium-doped non-cubic fluorapatite (Ca 10 (PO 4 ) 6 F 2 : FAP) ceramics composed of randomly oriented grains approximately 100 nm in size. Laser operation was evaluated under quasi-continuous-wave (QCW) operation, and a slope efficiency of 20% was achieved even in ceramics with randomly oriented crystal grains. Passively Q-switched pulse-burst operation was also examined using a Cr 4+ :YAG saturable absorber, yielding a pulse width of 1.9 ns and a maximum peak power of 2.5 kW. These results demonstrate the potential of non-cubic ceramic gain media for high-performance laser applications and support their further development for advanced laser technologies.
Abstract Elongated InAs quantum dashes on InP introduce polarization anisotropy that limits polarization-insensitive photonic devices. We evaluate InAs quantum dots grown using a GaAs insertion layer that suppresses dash formation. Room-temperature polarization-resolved photoluminescence shows that the degree of linear polarization (DoLP) decreases from 0.3227 ± 0.0052 for a dash-dominant reference to 0.0382 ± 0.0029 for a dot-dominant sample. Broad-area lasers fabricated from eight stacked dot layers show no statistically significant threshold-current dependence on cavity orientation over 600–1200 µm cavities. These results indicate optically near-isotropic InAs quantum dots on InP grown using the GaAs insertion layer.
Abstract A wavelength-selective retroreflector based on guided-mode resonance (GMR) was proposed for an external cavity mirror of semiconductor lasers. The device, called a focusing cavity-resonator-integrated GMR filter (F-CRIGF), consists of a focusing grating coupler (FGC) integrated in a distributed-Bragg-reflector cavity on a bottom mirror. The F-CRIGF was designed for a 1550-nm-wavelength Gaussian beam whose axis is tilted by 20 degrees from the device’s surface normal. The FGC length and the focal length were 30 μm and 31.2 μm, respectively. A peak retro-reflectance of 68% with a 1.5-nm bandwidth was predicted by two-dimensional finite-difference time-domain simulation.
Abstract Out-of-field neutron dose evaluation is important for radiation protection during boron neutron capture therapy (BNCT). However, no commercial detector is available for measuring the neutron ambient dose equivalent H* outside the irradiation field. Establishing a reliable H* evaluation method is essential for the international standardization of BNCT. In this study, a prototype neutron detector was evaluated using a cyclotron-based epithermal neutron source (C-BENS). The ratio of the measured to calculated H*, based on ICRP Publication 116, ranged from 0.21–0.56 at lateral distances of 10–150 cm from the beam aperture center. This discrepancy is likely due to the difficulty in accurately reproducing the experimental geometry in the Monte Carlo simulation used to calculate the reference H*. These results provide a basis for improving H* evaluation methods and developing standardized radiation protection procedures for BNCT.
Abstract Cultured neuronal networks are promising biological information-processing units for biohybrid systems. While these systems must ultimately work under atmospheric conditions, the neuronal activity is difficult to sustain outside an incubator. Here, by comparing neuronal spheroids with and without collagen, we show that collagen gel embedding enables microelectrode array recording of their spontaneous activity in air. Although the embedding increased the distance between the spheroids and electrodes and thereby reduced the recorded signal amplitude, the collagen-embedded spheroids retained detectable activity for approximately 30 min under atmospheric conditions. In contrast, spheroids without collagen showed a more rapid decline in activity. These findings suggest that collagen gel preserves a hydrated microenvironment around the spheroids and could extend the window for extracellular recording outside an incubator without requiring bulky temperature- and humidity-control systems.
