S-1 photocathode response linearity and dynamic range with picosecond 1.06 micron laser pulses

Lawrence Livermore Laboratory developed a semiautomatic test set for making linearity measurements of ICTs (image converter tubes) and photodiodes. This test set, using a 36-ps laser pulse at 1.06 microns, provided much-needed information on the operating characteristics of these components for picosecond research applications. These measurements provided evidence that an ICT must have greater than 5/micro a/w sensitivity to ensure its output-input linearity. Also, the photoelectric current range of a photodiode can be considerably greater than its linear limit when the unit is saturated. In this study, 44-mm photodiodes with a linear photoelectric current range limit of 60 A were found to produce from 200 to 600 A when saturated. Likewise, saturated 20- and 10-mm photodiodes produced currents three to seven times their normal linear limits (14 to 20 A for the 20-mm diodes and 7 A for the 10-mm diodes). Finally, all of these current limits are roughly proportional to diode bias.