Dispersion Scan Frequency Resolved Optical Gating For Evaluation of Pulse Chirp Variation

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.