High sensitivity autocorrelation using Light Emitting Diode

Pico- and femto-second pulses are becoming powerful tools in chemistry, biology, medicine, and industry. High price for auto-correlators, nonlinear crystals and their low quantum efficiency of Second Harmonic Generation in Near Infrared region have encouraged the search of alternative approaches. It has been demonstrated recently that Si and GaAsP photodiodes and CdS photoconductive cell [1] and even unbiased Light Emitting Diodes (LED) [2] can replace nonlinear crystals and photodetectors in autocorrelators for characterisation of powerful ultrashort laser pulses. Specially fabricated waveguide structures have provided much higher sensitivity due to longer length of interaction [3,4]. However, waveguide configuration suffers from low coupling efficiency into waveguide and reduction of temporal resolution due to dispersion.