The photon counting detector modules of the PDM series are all solid-state instruments designed and manufactured by Micro-Photon-Devices (MPD) of Bolzano, Italy. They have photon detection efficiency of 49% at 550 nm and generate a TTL output pulse per detected photon. With fast-timing option (additional circuit card installed inside the module) they provide better than 50 ps FWHM photon timing resolution (NIM output pulse) for a wide range of detection wavelengths. The excellent photon detection efficiency and superior timing resolution is obtained through the use of epitaxial silicon Single Photon Avalanche Diodes (SPAD) and patented integrated Active Quenching Circuits (iAQC), specifically designed and optimized for time-resolved photon counting applications.

The SPADs are available with a diameter of the active area of 20, 50 and 100 µm. They cover a spectral range from about 400 nm to 900 nm with the highest quantum efficiency in the VIS range around 550 nm. They are extremely robust and can withstand continuous exposition to daylight. Their superior timing makes them a real alternative to photomultiplier tubes for many applications. Especially above 470 nm the temporal response is even comparable to MCP-PMTs and an Instrument Response Function (IRF) around 50 ps can be reached with the PicoHarp 300 along with a suited short pulsed laser. Moreover, the high quantum efficiency make them an ideal detector for single molecule applications, like Fluorescence Correlation Spectroscopy (FCS) or Fluorescence Lifetime Imaging (FLIM), especially as the SPAD output has a stable timing even at count rates exceeding 1 Million counts/sec.