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Light Detectors

Room Temperature PMT Housing   

ISS photomultiplier tubes housings are compact units designed for both photon counting and frequency-domain data acquisition; they are coupled to the ISS spectrofluorometers through a M28x1 threaded flange. An adapter for coupling the PMT housing to a 10 mm fiber bundle is available.

The housing is designed for side-on photomultiplier tubes (model R928 by Hamamatsu and socket-compatible PMTs). The housing includes the high voltage power supply operating up to 1,200 Volt and requires a ±15 V, DC voltage for operation. In photon counting mode of operation, the PMT housing operates at maximum voltage. In analog mode of operation, the voltage can be changed manually through an external potentiometer positioned on the housing; or, automatically, through the computer. The latter form of control requires a D/A converter circuitry, a standard feature on all the ISS spectrofluorometers.

The frequency response of the housing is up to 700 MHz. In operation, the effective frequency response is determined by the PMT utilized for detection; Selected PMTs Model R928 feature a frequency response up to 600 MHz. The radiofrequency signal is injected through a BNC jack located on the back panel of the PMT.

Cooled PMT Housing   

Cooling the photomultiplier tube, reduces the dark current and increases the dynamic range. ISS offers a cooled photomultiplier tube recommended for use in photon counting detection when a high instrument sensitivity is required. The housing is cooled by a thermoelectric element (Peltier cooling) which allows the temperature to be set as low as -28°C. A flow through cooling device is necessary to remove excess heat from the Peltier element.

Microchannel Plate Detector   

For the detection of light modulated above 500 MHz, a Microchannel Plate Detector (MCP) photomultiplier tube is required. The ISS MCP housing is designed for easy installation on ISS fluorometers. The optical axis is 63.4 mm, and an M28-threaded adapter couples the MCP to the instrument. The compact housing contains the entire electronics for processing of frequency-domain signal, including the high voltage power supply, the power amplifier and the mixer. A -12 Volt input signal is required for operation. The housing is built for the Hamamatsu R2566U MCP although other MCPs are easily accommodated.