Abstract

Second-order autocorrelation of ultrashort laser pulses by using two-photon-induced photocurrent in semiconductors offers several advantages compared with traditionally employed combination of a second harmonic (SH) crystal and a photomultiplier tube. A low-priced commercially available photodiode [1] allows to overcome principal drawbacks of SH-based autocorrelation: limited phase-matching bandwidth and wavelength-dependent sensitivity of the light detector leading to a spectral filtering effect, pulse broadening due to crystal bulk dispersion, low conversion efficiency which decreases with increase of SH bandwidth, high cost and manufacturing problems associated with thin SH crystals. A significant advantage of incorporating a semiconductor photodiode into autocorrelation measurements is that the desired two-photon response and the transformation of light into electric current are combined into a single solid-state 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 from the autocorrelation trace and the pulse spectrum by means of a two-stage iterative algorithm [2]. In this contribution we demonstrate that due to absence of spectral filtering effect and high dynamic range of quadratic response to the incident intensity in a GaAsP photodiode [1], correct retrieval of temporal profile and phase from autocorrelation and spectrum can be achieved for ultrashort laser pulses with bandwidths as large as 130 nm and pulse energies as low as several pJ.

© 1998 IEEE