Abstract

A novel dispersion-free autocorrelator (DFA) has been developed to achieve subfemtosecond temporal resolution. Autocorrelation methods are widely used to measure ultrashort pulses because of their high temporal resolution. However, when the pulse duration is reduced to femtosecond region, pulse broadening by optical components occurs, owing to group velocity dispersion (GVD), and this broadening causes error in pulse-duration measurements. Because GVD depends on spectrum width, shorter pulses increase the broadening effect. To eliminate such pulse broadening, each optical component in the autocorrelators must be ultra thin or dispersion-free. Our novel autocorrelator, which is a noncollinear configuration, consists of a focusing concave mirror, an ultrathin pellicle 5 m beam splitter, corner reflectors, and a 100 m KDP crystal to generate the second harmonic of the laser pulses. Each component causes subfemtosecond time broadening for 10 fs pulses at 620 nm. For example, broadening of a 10 fs pulse due to the pellicle is only 10.0004 fs (negligible) while the KDP crystal broadens the 10 fs pulse to 10.21 fs. Using a colliding-pulse mode-locked (CPM) ring dye laser generating 60 fs pulses at 620 nm, the characteristics of DFA have been investigated by comparing them with an ordinary, noncollinear autocorrelator. Various DFA designs, along with their characteristics and GVD effects, will be discussed in detail.

© 1990 Optical Society of America