Signal-induced fluorescence in photomultipliers in differential absorption lidar systems

Signal-induced bias (SIB) superimposed on the tail of lidar signals detected by photomultiplier tubes (PMT's) has long been recognized as significant interference in lidar data retrieval. Analysis of the data from a lidar transmitting in the horizontal direction revealed that SIB is a well-shaped pulse and is thus called a signal-induced pulse (SIP). The SIP starts near the end of the signal and has an exponentially decaying tail. The decay time constant is negatively correlated with the pulse rise time. The origins of afterpulses discussed in the literature could not explain the cause of the SIP. This research leads to the hypothesis that the SIP is the fluorescence emitted from the PMT wall that is impinged by ions in the PMT. A model was developed, and the results show good agreement with the data. This model is applied to remove SIP's during processing of data from an ozone-profiling lidar.