Entropy-based Time-Varying Window Width Selection for Nonlinear type Time-Frequency Analysis

We propose a time-varying optimal window width (TVOWW) selection scheme to optimize the performance of several nonlinear-type time-frequency analyses, including the reassignment method, and the synchrosqueezing transform (SST) and its variations. A window rendering the most concentrated distribution in the time-frequency representation (TFR) is regarded as the optimal window. The TVOWW selection scheme is particularly useful for signals that comprise fast-varying instantaneous frequencies and small spectral gaps. To demonstrate the efficacy of the method, in addition to analyzing a synthetic signal, we study an atomic time-varying dipole moment driven by two-color mid-infrared laser fields in attosecond physics.