What has been the conventional method for measuring or characterizing laser pulses?
Autocorrelation was the first technique used to measure the intensity vs. time of an ultrashort laser pulse. Invented in the 1960s, autocorrelation uses a laser pulse to measure itself, splitting the pulse into two, variably delaying one with respect to the other, and spatially overlapping them in some instantaneously responding nonlinear optical medium. Since their introduction, autocorrelators have had severe limitations: at best, they yield a poor measure of a laser pulse’s width, and, worse, they say nothing at all about the pulse’s phase or spatiotemporal distortions. Moreover, autocorrelators are complex, difficult to set up, and no algorithm exists for retrieving the pulse intensity or any other information from an autocorrelation.
