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an-péri ixte d m cy o iffer tha n im exp 50 used for extremely weak pulses, which is one of the main Dorrer et al. Vol. 17, No. 10 /October 2000 /J. Opt. Soc. Am. B 1795reasons for its widespread use in femtosecond spectros-copy. A complete measurement of the electric field thus allowed the transposition of two-dimensional nuclear magnetic resonance to the optical domain,16,17 as well as the time-resolved measurement of photon-echo emissions.18–21 Spectral interferometry has also been used for measuring the linear dispersion of materials,22 for characterizing the complex dielectric function of semi-conductor nanostructures,23 and for discriminating be-tween coherent and incoherent radiation in secondary emission from semiconductor quantum wells.24,25 Fi-nally, spectral interferometry is a key ingredient in a re-cent nonlinear pulse-measurement technique, known as spectral phase interferometry for direct electric field re-construction. This very efficient and noniterative tech-nique makes use of spectral interferences between two frequency-sheared replicas of the unknown pulse.15,26–29 Despite the widespread use of spectral interferometry, there have been few detailed studies up to now on its re-(FFT) algorithms are most efficient when the data points are evenly spaced in the frequency domain. In Section 4 we discuss limitations arising from the finite spectral resolution of the spectrometer, as well as from the use of a detector made of a finite number of pixels. We will show that such effects can be carefully characterized and in most cases corrected for. Finally, we propose in Section 5 an improved FTSI procedure, which relies on the same ex-perimental scheme but involves more careful data pro-cessing