1.9 picosecond optical temporal analyzer using 1.2 picosecond photodetector and gate

The authors report on a novel photoconductive-type detector with a response time of 1.2 ps. This is the fastest photodetector to date. It is based on low-temperature-grown GaAs and uses interdigitated electrodes of 0.2 mu m spacing to match the carrier transit time to the carrier lifetime. The responsivity is 0.1 A/W. The detector can be driven to an on-state resistance of a few of ohms, with the response time increasing to only 1.5 ps. The photodetector can therefore also function as a picosecond photogate. The two components have been combined to form an all-semiconductor optical temporal analyzer. The system response time is 1.9 ps, with a minimum detectable average power of 500 pW. The technique is jitter-free, permitting long integration times. Ultraweak picosecond fluorescence and scattering experiments, as well as other ultrafast phenomena can be time-resolved using this relatively simple tool.<>