Detection of laser pulse asymmetry by three-photon fluorescence

It is shown that the well known loss of asymmetry information in single time delay (STD), three-photon fluorescence (3PF) measurements of short laser pulses can be recovered by splitting the main beam into two parts with distinctly nonequal intensities before recombining them in the fluorescent media. A mathematical formulation is presented which relates the ability to recover asymmetry information with the loss of contrast brought about by the use of nonequal intensities, where both depend upon the temporal position along the pulse. The characteristics of the asymmetry detectability are affected by the degree of mode locking of the laser pulse. A numerical simulation confirms the results.