Frequency-resolved optical gating (FROG) has become an established method of assessing the amplitude and phase profiles of ultrashort laser pulses. Second-harmonic-generation (SHG) FROG is the most widely used version, because it is relatively simple to set up and operate. However, for some complex pulse shapes it tends to produce false results. Here we discuss the reconstruction of multiple-pulse structures, a situation in which SHG FROG frequently fails. We suggest a modification of the standard procedure and demonstrate that the rate of false results is significantly reduced. We also discuss reconstruction in the presence of noise. A procedure for obtaining error bars is given; these error bars allow us to gauge the quality of the reconstruction. (C) 2015 Optical Society of America
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