“…For example, in the previous measurements on optimally-doped (OD) YBa 2 Cu 3 O 7-δ (YBCO) samples, the observed sign of time-resolved differential reflectivity (ΔR/R) was reported to be either positive or negative. 9,11,25,26 This fundamental discrepancy was attributed to the dependence of ΔR/R on several factors including laser power, 15,23 wavelength, 25,27 polarization, 25,28 and repetition rate 24,29 . Furthermore, in a recent effort to uncover the transient optical signatures of the pseudogap (PG) phase, [11][12][13][14]28,[30][31][32] and elucidate a possible relationship between the PG state and SC state in OD YBCO [31][32] , the PG phase was either identified as a weak transient feature 11,30 or found to be completely absent from the spectra.…”