We have realized a high-detection-efficiency photon number resolving detector at an operating wavelength of about 850 nm. The detector consists of a titanium superconducting transition edge sensor in an optical cavity, which is directly coupled to an optical fiber using an approximately 300-nm gap. The gap reduces the sensitive area and heat capacity of the device, leading to high photon number resolution of 0.42 eV without sacrificing detection efficiency or signal response speed. Wavelength dependent efficiency in fiber-coupled devices, which is due to optical interference between the fiber and the device, is also decreased to less than 1% in this configuration. The overall system detection efficiency is 98%±1% at wavelengths of around 850 nm, which is the highest value ever reported in this wavelength range.

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Microtextured polydimethylsiloxane sheets exhibit an exceptionally low reflectance of ≲0.0005 across the entire thermal infrared wavelengths while maintaining high resilience.

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We developed a calorimeter for determining absolute terahertz (THz) power. The calorimeter is based on a DC substitution method using an isothermal temperature-control technique. A neutral-density optical filter glass was used as a volume absorber, and its THz absorption was evaluated by a time-domain spectrometer. Highly sensitive measurement of the absolute THz power was experimentally achieved in the range from the submicrowatt to microwatt level at room temperature. Power measurement of a continuous-wave THz source using a photomixer was demonstrated. This calorimeter is expected to demonstrate the traceability of THz power at a submicrowatt level.

The geometric locations of ion traversals in mammalian cells constitute important information in the study of heavy ion-induced biological effects. We employed a contact microscopy technique, which was developed for boron imaging in boron neutron capture therapy to the irradiation mammalian cells by low-energy heavy ions. This method enables the simultaneous visualization of mammalian cells as a relief on a plastic track detector, CR-39, and the etch pits which indicate the positions of ion traversals. This technique provides visual geometric information about the cells and ion traversal, without any specially designed devices or microscopes. Only common laboratory equipment, such as a conventional optical microscope, a UV lamp, and commercially available CR-39 is required. To validate this method, CHO-K1 and HeLa cells were cultured on the CR-39 surface and then irradiated with low-energy Ar and Ne ions, respectively. The positions of induced DNA double strand breaks were detected as gamma-H2AX fluorescent spots, which coincided with the positions of the etch pits in the cell relief image.

Spectral supralinearity of silicon photodiodes in visible light was investigated. The experimental spectral supralinearity results were compared with the calculation results using a device simulator, PC1D that includes the front surface recombination parameters, and these comparison results were in reasonable agreement for a silicon photodiode. These comparison results show that supralinearity in visible light clearly occurs with a front surface charge density of more than 10¹² cm^-2 and the included parameters are adequate for quantitatively predicting the internal quantum efficiency of silicon photodiodes.