Development of a multi-pixel photon sensor with single-photon sensitivity

A multi-pixel photon sensor with single-photon sensitivity has been developed, based on a technology of a hybrid photo-detector (HPD) consisting of a photocathode and a multi-pixel avalanche diode (MP-AD). The developed HPD has a proximity focused structure, where a photocathode and an MP-AD are facing each other with a small gap of 2.5 mm. The MP-AD, which has an effective area of 16x16 mm2 composed of 8x8 pixels, has been specially designed for the HPD. The gain of the HPD reaches 5x10^4, sufficiently high to detect single photons with a timing resolution better than 100 ps. Number of photoelectrons up to four can be clearly identified in a pulse-height spectrum as distinct peaks, thanks to the low noise characteristics of the HPD. It is also demonstrated that the HPD can be operated with good performance in a magnetic field as high as 1.5 TComment: 39 pages, 22 figures, submitted to Nucl. Intr. and Meth.

Low-Light Photodetectors for Fluorescence Microscopy

Over the years, fluorescence microscopy has evolved and has become a necessary element of life science studies. Microscopy has elucidated biological processes in live cells and organisms, and also enabled tracking of biomolecules in real time. Development of highly sensitive photodetectors and light sources, in addition to the evolution of various illumination methods and fluorophores, has helped microscopy acquire single-molecule fluorescence sensitivity, enabling single-molecule fluorescence imaging and detection. Low-light photodetectors used in microscopy are classified into two categories: point photodetectors and wide-field photodetectors. Although point photodetectors, notably photomultiplier tubes (PMTs), have been commonly used in laser scanning microscopy (LSM) with a confocal illumination setup, wide-field photodetectors, such as electron-multiplying charge-coupled devices (EMCCDs) and scientific complementary metal-oxide-semiconductor (sCMOS) cameras have been used in fluorescence imaging. This review focuses on the former low-light point photodetectors and presents their fluorescence microscopy applications and recent progress. These photodetectors include conventional PMTs, single photon avalanche diodes (SPADs), hybrid photodetectors (HPDs), in addition to newly emerging photodetectors, such as silicon photomultipliers (SiPMs) (also known as multi-pixel photon counters (MPPCs)) and superconducting nanowire single photon detectors (SSPDs). In particular, this review shows distinctive features of HPD and application of HPD to wide-field single-molecule fluorescence detection

Lossless photon recording of two-color fluorescence correlation spectroscopy for protein dynamics investigations from nanoseconds to milliseconds

Nanosecond-resolved fluorescence correlation spectroscopy (ns-FCS) based on two-color fluorescence detection is a powerful strategy for the investigation of fast dynamics of biological macromolecules labeled with donor and acceptor fluorophores. The standard methods of ns-FCS utilize two single-photon avalanche diodes (SPADs) for the detection of single-color signals (four SPADs for two-color signals) to eliminate the afterpulse artifacts of SPAD at the expense of the efficiency of counting fluorescence photons. In this study, we demonstrated that hybrid photodetectors (HPDs) enable the lossless recording of all the fluorescence photons in ns-FCS based on the minimal system using only two HPDs for the detection of two-color signals. Unexpectedly, HPD was found to show afterpulses at the yield (<10-4) much lower than that of SPADs (~10-2), which could still hamper the correlation measurements. We demonstrated that the simple subtraction procedure could cancel the afterpulse artifacts clearly. The developed system showed the better signal to noise ratio compared to the conventional method for the correlation measurements in the time domain longer than a few nanoseconds. The fast chain dynamics of the B domain of protein A in the unfolded state was observed by the new method

群馬県の古墳研究史における尾崎喜左雄博士の古墳調査の意義

Departmental Bulletin Paper本論では、群馬大学名誉教授である尾崎喜左雄博士（以下、尾崎氏）の古墳調査が100年近く続く群馬県の古墳研究の歴史の中で、どのように寄与したのかについて考察した。 　尾崎氏は、昭和18年に群馬師範学校教授に着任したのち、昭和20年代前半から、昭和40年代半ばまでの間に県内各地で360基以上の古墳の調査を実施しているが、その中から、渋川地域、太田地域、高崎地域における尾崎氏の古墳調査の取り組みについてとりあげ再検証した。 　そして、尾崎氏の古墳調査を時系列で整理し、昭和時代における群馬県の文化財保護史の中に位置づけた。その結果、戦前の帝室博物館、郷土史家や知識人による発掘と昭和40年代後半以降現在まで続く地方自治体等による発掘という２つの異なる古墳調査の体制・動向の間に尾崎氏の古墳調査が位置づけられることが明らかになり、このことが、今日の古墳研究に大いに寄与していることが再確認された