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Sum frequency generation between a Ti:Sapphire beam and white light continuum is performed to obtain spectral information from GaAs(001). The experimental difficulties are analyzed and possible solutions and extensions to the technique proposed. The phase of second harmonic generation (SHG) is measured using a frequency domain technique. Phase shifts in GaAs under azimuthal rotation are observed and explained. The phase of the surface second order susceptibility tensor elements of Si is measured. For the first time SHG phase from Si/SiO2 and Si/SiO2/Hf-silicate is measured with a temporal resolution better than one second. Si/SiO2/Hf(1−x)SixO2 stack structures are studied using rotational anisotropic, spectroscopic, and time dependent SHG. It is found that the signal is affected by Si content (x) and by annealing history of the samples. The results show that SHG is sensitive to the phase separation of the silicates bulk due to spinodal decomposition. A heuristic model based on Hf-O-Si polarizable units that explains the observed trends is presented.