Figure 4: Schemes of stationary and induced impurity absorption spectra formation and of the optical transitions, explaining -DLSS: regime of laser modulation of TSA by photoionization, at the absence of TPA-generation . (a) and (d). At small intensity, “dark” filling of the compensated donors, only the band of photoneutralization is observed. (b) and (e) At the intensities of probe light, breaking a dark-filling of DL’s, photoionization band appears. (f) Changes of TSA spectra as a result of laser modulation. (c) and (g) Induced absorption spectrum.