We have found optical photoinduced second harmonic generation in pyrene molecular crystals photoinduced by intrinsic defects. A correlation between the number of macro-vacancies (defects) measured by positron annihilation and second-order nonlinear optical susceptibilities indicates the appearance of additional non-centrosymmetry in the electron charge density distribution caused by the defects. Simultaneously, changes in the kinetics of phenomena in the picosecond time regime are demonstrated. The latter indicate the essential role of intra- and intermolecular contributions in the observed phenomena.

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In this work, we have studied bismuth telluride (Bi2Te3) thin films on Si(100) and SiO2/Si(100) substrates grown by Hot Wall Epitaxy (HWE) technique. The morphology of the surface was controlled by Atomic Force Microscopy (AFM). Reflection and transmission experiments in the mid‐infrared (MIR) spectral range were performed at room temperature. We have deduced the frequency dependence of the absorption coefficient. The refractive index was determined in the mid‐infrared (MIR) spectral range for these samples and the energy band gap was evaluated.