  The commonly used methods to characterize ultrafast laser pulses, such as
frequency-resolved optical gating (FROG) and dispersion scan (d-scan), face
problems when they are used on pulses with a chirp varying within the laser
beam or the acquisition time. The presence of such chirp variation can be
identified by a discrepancy between the measured FROG and d-scan traces and
their reconstructed counterparts. Nevertheless, quantification of the variation
from the experimental data is a more complex task. In this work, we examine the
quantification of chirp variation based on three different pulse
characterization techniques. Two commonly used techniques FROG and d-scan are
compared to a new method dispersion scan FROG (D-FROG) that combines the idea
of dispersion scanning with the FROG method. By using the three techniques, we
analyze the chirp variation of pulses generated from NOPA together with pulses
processed by a 4f-pulse shaper without and with SLM-adjusted phase. We evaluate
the performance of the new D-FROG method for the chirp variation estimate and
the improved reconstruction of the measured results. Furthermore, we discuss
the origin of chirp variation in each of the measurements by using fast-scan
autocorrelation traces.
