Ultra-short pulse characterization using a reference laser pulse

We propose a novel and simple technique to determine the temporal profile of ultra-short laser pulses uniquely from a measured auto-correlation spectrum. It involves forming a sequence of two laser pulses spaced by a time delay tau, the first one being the pulse to be characterized and the second one a reference pulse. This sequence is sent through any device that measures the Fourier transform (FT) magnitude of the sequence's temporal profile, such as a classical optical auto-correlator. This FT magnitude is then processed analytically using a novel algorithm to retrieve the temporal profile of the sample pulse unambiguously. The reference pulse can be either an unchirped symmetric pulse or any pulse with a known profile. This requirement does not constitute a limitation because once the temporal profile of a given pulse has been characterized by this technique, even though it may not be an unchirped symmetric pulse, this pulse can be used as the reference pulse to determine the profile of any other ultra-short pulse. Compared to other measurement techniques, such as frequency-resolved optical gating, our technique is much faster and simpler, in terms of both experimental and computational complexity. Simulations also show that the profile recovery is quite accurate even in the presence of strong noise on the measured FT magnitude.