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We present a multicolor multiphoton fluorescence microscope with single-photon counting sensitivity. The system integrates a standard multiphoton fluorescence microscope, an optical grating spectrograph operating in the UV-Vis wavelength region, and a 16-anode photomultiplier tube (PMT). The major technical innovation is in the development of a multichannel photon counting card (mC-PhCC) for direct signal collection from multi-anode PMTs. The electronic design of the mC-PhCC employs a high-throughput, fully-parallel, single-photon counting scheme along with a high-speed electrical or fiber-optical link interface to the data acquisition computer. There is no electronic crosstalk among the detection channels of the mC-PhCC. The collected signal remains linear up to an incident photon rate of 10(8) counts per second. The high-speed data interface offers ample bandwidth for real-time readout: 2 MByte lambda-stacks composed of 16 spectral channels, 256 x 256 pixel image with 12-bit dynamic range can be transferred at 30 frames per second. The modular design of the mC-PhCC can be readily extended to accommodate PMTs of more anodes. Data acquisition from a 64-anode PMT has been verified. As a demonstration of system performance, spectrally resolved images of fluorescent latex spheres and ex-vivo human skin are reported. The multicolor multiphoton microscope is suitable for highly sensitive, real-time, spectrally-resolved three-dimensional imaging in biomedical applications.

In the work presented here we built and evaluated a single-channel neutron detection unit consisting of a ZnS:6 LiF scintillator with embedded WLS fibers readout by a SiPM. The unit has a sensitive volume of 2.4 x 2.8 x 50 mm 3 ; 12 WLS fibers of diameter 0.25 mm are uniformly distributed over this volume and are coupled to a 1 x 1 mm 2 active area SiPM. We report the following performance parameters: neutron detection efficiency ∼ 65 % at 1.2Å, background count rate < 10 −3 Hz, gamma-sensitivity with 60 Co source < 10 −6 , dead time ∼ 20 µs, multi-count ratio < 1 %. All these parameters were achieved up to the SiPM dark count rate of ∼ 2 MHz.We consider such detection unit as an elementary building block for realization of onedimensional multichannel detectors for applications in the neutron scattering experimental technique. The dimensions of the unit and the number of embedded fibers can be varied to meet the specific application requirements. The upper limit of ∼ 2 MHz on the SiPM dark count rate allows to use SiPMs with larger active areas if required.

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Two single channel detection units for thermal neutron detection are investigated in a neutron beam. They consist of two ZnS/ 6 LiF scintillating layers sandwiching an array of WLS fibers. The pattern of this units can be repeated laterally and vertically in order to build up a one dimensional position sensitive multi-channel detector with the needed sensitive surface and with the required neutron absorption probability. The originality of this work arises from the fact that the WLS fibers are read out with SiPMs instead of the traditionally used PMTs or MaPMTs. The signal processing system is based on a photon counting approach. For SiPMs with a dark count rate as high as 0.7 MHz, a trigger efficiency of 80% is achieved together with a system background rate lower than 10 −3 Hz and a dead time of 30 µs. No change of performance is observed for neutron count rates of up to 3.6 kHz.