The detection of the smallest amounts of light is gaining in importance in medical technology and diagnostics. In principle, photon multipliers (PMTs) would be suitable for this type of application; however, they are disadvantageously sensitive to magnetic fields. In addition, they require a high operating voltage.
Avalanche photodiodes (APDs) are thus ideal for photon counting. The components of the SAP500 series are based on a “reach through” structure featuring excellent quantum efficiency, extremely low noise, and low dark current.
The SAP500 series, which possesses an active area of 500 µm, can be operated in linear mode at VR < VBR, reaching an internal gain of 250 or more. In order to detect individual photons, this series is operated in Geiger mode. The APD is then operated at a voltage above the breakdown voltage, VR > VBR.
The new SAP500 series is, hence, particularly suitable for applications in which the weakest light signals, down to the individual photons, have to be quantified and timely resolved. Examples of this include LIDAR, spectroscopy, fluorescence measurements, or photon counting.
Compared to photon multipliers, the less expensive APDs have the following advantages: compact design, insensitivity to magnetic fields, robustness, longer lifetime, very good time resolution, lower operating voltage.
The SAP500 comes in a hermetically-sealed TO-46 housing. Versions with a single-stage thermoelectric cooler (in a TO-37 housing) or a two-stage TEC (in a TO-8 housing) are also available.
