  This article describes a simplified reconstruction algorithm for frequency
resolved optical gating (FROG) measurements of highly (monotonically) chirped
pulses. The FROG traces are calculated using the stationary phase
approximation, significantly reducing the data size and convergence time
compared to discrete Fourier transform based methods. The method is verified
via second harmonic generation FROG simulations and measurements of pulses
centred at 800nm with a bandwidth of 55nm stretched to 32ps at the 1% intensity
level, corresponding to a time-bandwidth product of 830.
