The nonlinear optical properties of gold nanoparticles with different densities of particles on indium–tin oxide (ITO) substrates of different origins are investigated. The coherent photoinduced nonlinear optical effect at 1.32 µm reveals a marked dependence on the interparticle distance and density. The decrease of the interparticle distance with the increase of Au nanoparticle density favours the photoinduced optical second harmonic generation. The maximal second-order optical susceptibility attained at a wavelength of 1.32 µm corresponds to the value of about 4.56 pm V−1. The predominant role of the interface between the Au nanoparticles and the ITO substrate is shown.

Studies of the second-order nonlinear optical susceptibilities of six NLOphores bearing di(tri)cyanovinyl acceptor groups linked to (bi)thiophene heterocyclic donor systems were performed for the first time in polymethyl methacrylate (PMMA) matrices with a 1064 nm laser working in the 20 ns time pulse regime. Absorption spectra and DFT calculations were also performed. This multidisciplinary study showed that modulation of the optical (linear and nonlinear) properties can be achieved by increasing the length of the -conjugated heterocyclic system (thiophene vs. bithiophene), the strength of the electron donor groups (HMeO/EtOEt2N) as well as the strength of the electron acceptor moieties (DCV vs.TCV, two vs. three electron withdrawing cyano groups). Due to the relatively high secondorder susceptibilities (0.08 to 6.45 pm/V), the studied push-pull chromophores can be denote as very potent NLOphores.

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