Measurement of interferometric autocorrelations: comment.

Conventional Michelson interferometers that are widely used for autocorrelation of ultrashort optical pulses are incapable of producing two identical replicas of an optical pulse, hence yielding a correct autocorrelation signal. The problem is acute when one records the interferometric autocorrelation of pulses consisting of just a few optical cycles. With the use of sub-10-fs pulses we demonstrate asymmetric autocorrelation traces recorded with a conventional Michelson interferometer, refer to previously reported results that exhibit the same deficiency, and elucidate the origin of the problem. A simple modification of the conventional interferometer configuration yields the correct fringe-resolved autocorrelation trace.