For many years, photon multiplier tubes (PMTs) were the gold standard for confocal optical systems. They are known for a very wide dynamic range and robustness. Semiconductor sensors, the avalanche photo diodes (APDs) were introduced for photon counting applications. They offer good parameters for correlation and time measurements, but lack dynamic range.
Recently, a new generation of detectors was introduced in confocal microscopes, the hybrid detectors (HyDs). These sensors combine the benefits of vaccum tube technology with the benefits of semiconductor avalanche technology. And in fact, they are true hybrids of both technologies.
This article reviews the important parameters of the three different sensor-approaches and compares their applicability for a series of biomedical measurement methods in order to find out, which sensor type is suited best for which type of application.