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A series of methacrylic styrylquinoline polymers have been synthesized and characterized by spectroscopic and nonlinear optical (NLO) investigations. The NLO properties of studied polymer compounds in the form of thin films prepared by a spin coating method have been investigated by means of second and third harmonic generation via Maker fringe setup with a laser source at 1064 nm and a pulse duration of 30 ps. The results show strong second harmonic signal dependence on polarization configurations. This second harmonic generation (SHG) response was enhanced by UV-irradiation at 366 nm and doping by ZnO nanoparticles (NPs) (100 nm), while the opposite effect was achieved for a third harmonic generation experiment. Thus, values of second and third order nonlinear susceptibilities were determined by theoretical calculations based on comparative models. The remarkable NLO results presented in this paper expose potential optoelectronic and photonic applications.

Optical nonlinearities in three-level asymmetric semiconductor quantum wells (QW) are analyzed (optical rectification, second harmonic generation (SHG)). The influence of permanent dipole moments on SHG conversion efficiency for various QW structures is investigated. It is found that as the pump photon wavelength increases so does the relative importance of the permanent dipole moments, provided the QW is resonant.

Strained silicon is a versatile new type of material, which has found application in microelectronics and integrated optics in the last years. Unlike ordinary silicon, it does not possess a centrosymmetric lattice structure. This allows for stimulation of nonlinear optical processes that involve second-order nonlinear susceptibility. Here, the dependence of the nonlinear susceptibility on the applied strain by means of reflected second-harmonic generation is investigated. This surface-sensitive technique is suitable for the investigation of bulk silicon strained by a layer of thermal oxide. The obtained relation between applied stress and susceptibility enhancement is compared to theoretical prediction based on an analytical model for the deformed silicon orbital. The knowledge of the stress-susceptibility dependence can be used to develop suitable photonic devices that benefit from second-order nonlinear processes in silicon.

Bu çalışmada, asimetrik kuantum kuyu yapılarının lineer olmayan optik özellikleri teorik olarak incelenmiştir. Bunun için, farklı sınırlandırıcı potansiyellere sahip kuantum kuyu yapılar göz önüne alınmıştır. Bu yapıların elektronik ve lineer olmayan optik özellikleri analitik ve nümerik olarak çalışılmıştır. İkinci ve üçüncü mertebe nonlineer optiksel özellikler yoğunluk matris formalizmi kullanılarak hesaplanmıştır. Hesaplanan optiksel süreçler şunlardır: Optiksel doğrultma, ikinci harmonik üretimi, üçüncü harmonik üretimi, nonlineer soğurma katsayısı ve şiddete bağlı kırılma indisi. Hesaplamalarda, kuyu genişliği, bariyer yüksekliği, sınırlandırıcı potansiyel frekansı ve elektrik alan gibi parametrelerin ve eksitonun etkileri de araştırılmıştır., In this study, the nonlinear optical properties of asymmetric quantum well structures are investigated theoretically. For this purpose, the quantum well structures having different confining potentials are taken into consideration. The electronic and the nonlinear optical properties of these structures are studied analytically and numerically. Second and third order nonlinear optical properties are calculated using the density matrix formalism. The calculated optical processes include optical rectification, second harmonic generation, third harmonic generation, nonlinear absorption coefficient and the intensity-dependent refractive index. In our calculations, the effects of the exciton and the parameters such as well width, barrier height, confining potential frequency and electric field are also investigated.