Amplitude and Phase Characterisation of Femtosecond Pulses in a Photodiode-Based Autocorrelator

Abstract

Second-order autocorrelation of ultrashort laser pulses by using two-photon-induced photocurrent in semiconductors offers several advantages compared with baditionally employed combination of a second harmonic (SH) cytal and B photomultiplier tube. A low-priced commercially available photodiode [I] sllows to overcome principal drawback of SH-based amcomelation: limited phaos matching bandwidth and wavelength.dependent sensitivity of the light detector leading to B spectral filtering effect, pulse brmdening due to crystal bulk dispersion, low conversion efficiency which decrease9 with increase of SH bandwidth, high cost and manufacturing problems associated with thin SH crystals. A siaificant advantage of incorporating a semiconductor photodiode into autocorrel&tioa measurements iE that the desired two-photon reoponre and ihe transformation of light into electric current are combined into a single nolid-stste device. It has been shown recently that for the vast majority of practically realisable pulses the complete phase and amplitude information could be rapidly recovered fmm the autocorrelation trace and the pulse spectrum by means of a two-stage iteratiw algorithm [Z]. In this convihurion we demonstrate that due to absence of spectrsl filtering effect and high dynamic range of quadratic response to the incident intensity in a GaAsP photodiode [I], correct retrieval of temporal profile and phase from autocorrelation and spectrum cm be