The PDM SPAD photon counting detector series are all solid-state instruments that detect light from 375 nm to 1000 nm wavelength range. They have a peak photon detection efficiency of 49% at 550 nm and generate a TTL output pulse per detected photon. Standard TTL pulses provide better than 250 ps timing resolution. Anyway, they also generate an additional output pulse, according to the NIM standard, able to provide better than 50 ps FWHM photon timing resolution.
The excellent photon detection efficiency and superior timing resolution is obtained through the use of custom epitaxial silicon Single Photon Avalanche Diodes (SPAD), an Active Quenching Circuits (AQC), specifically designed and optimized for photon counting applications which generates the positive TTL pulses, and a fast timing circuit board, always installed in PDM modules, which generates the negative NIM pulses. The SPAD is thermoelectrically (TEC) cooled and its temperature controlled, ensuring stabilized performance despite ambient temperature changes.
Thanks to the use of an AQC, it is also possible to gate on or off the detector. The PDM GATE IN input is thus very useful for switching on the detector only during specific time windows for better noise rejection and increased signal-to-noise ratio. The GATE IN input is very useful also to be used as an interlock input whenever the user wants to switch off the detector if an event occurs. The PDM GATE IN input is also not designed to be used as a fast-gated module. In the scientific literature, a fast-gated detector is a detector than can be switched from the OFF state to the ON state very precisely and in very short periods of times, with falling or rising times in the order of few hundreds of ps. In this case the MPD FastGATED SPAD should be purchased. The PDM GATE IN input, indeed, is not designed to accept high repetition external trigger signals and should be used to gate ON or OFF the SPAD with minimum gate ON or GATE OFF times in the orders of few tens of microseconds or longer.
The PDM maximum saturated count rate is the reverse of the deadtime, and it is 12-13 Mc/s. Of course, in order to avoid non-linearity errors in counting applications, a maximum count rate of at least four or five times smaller than the saturation level is recommended. The module is fully protected against light overload.
The PDM series is available with two optical interfaces: a free space optical window and a fibre connectorised version that guarantees > 80% coupling efficiency with selected fibres.