PRACTICAL ISSUES IN ULTRASHORT-LASER-PULSE MEASUREMENT USING FREQUENCY-RESOLVED OPTICAL GATING

We explore several practical experimental issues in measuring ultrasho rt laser pulses using the technique of frequency-resolved optical gati ng (FROG). We present a simple method for checking the consistency of experimentally measured FROG data with the independently measured spec trum and autocorrelation of the pulse. This method is a powerful way o f discovering systematic errors in FROG experiments. We show how to de termine the optimum sampling rate for FROG and show that this satisfie s the Nyquist criterion for the laser pulse. We explore the low- and h igh-power limits to FROG and determine that femtojoule operation shoul d be possible, while the effects of self-phase modulation limit the hi ghest signal efficiency in FROG to 1%. We also show quantitatively tha t the temporal blurring due to a finite-thickness medium in single-sho t geometries does not strongly limit the FROG technique. We explore th e limiting time-bandwidth values that can be represented on a FROG tra ce of a given size. Finally, we report on a new measure of the FROG er ror that improves convergence in the presence of noise.