(color online) ((a) and (b)) Time-frequency distributions of the electron dipole acceleration throughout recombination spanning 820 a.u.–1050 a.u. in the G case and in the U case, respectively. (c) Dependence of harmonic order on ionization time (circles) and emission time (dots) of the electron in the multicycle laser field. The laser parameters are the same as those in Fig. 2. ((d) and (e)) Evolving relative phase differences in the corresponding ionization time for the G case and the U case, respectively.