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Nonlinear optical materials play important roles in optics and photonics. In order to improve the performance of these materials, in this paper, we tried to find effective methods for controlling the nonlinear responses of thiazine dyes. Our experimental results indicate that molecular linear properties, media polarity, concentration and excitation beam properties with different contributions play significant roles on the saturable and reverse saturable absorption characteristics of thiazine dyes. In real, competition between these effective parameters leads to appearance of various third order nonlinear responses. Although by excitation wavelengths near the absorption peaks and at high powers, dye molecules tend to indicate reverse saturable absorption characteristics in polar protic solvents by increasing the concentration, saturable absorption characteristics were observed in polar aprotic solvents. Furthermore, the samples displayed the same behaviors in different solvent media at low powers and for excitation wavelengths far from absorption peaks. Therefore, by controlling the nonlinear responses of thiazine dyes, these materials can indicate both saturable and reverse saturable absorption characteristics that increase their applications in optics and photonics devices. [ABSTRACT FROM AUTHOR]

The naturally occurring yellow-orange curcumin with wide applications in medical, biological and chemical phenomena have drawn considerable attention during the last years. The properties of molecular surrounding media can modify its various characteristics. In this paper, tautomerism of curcumin was investigated in the wide variety groups of solvents. In this case, photo-physical properties of curcumin in enol, diketone and deprotonated forms were investigated separately in polar and low polar solvents at room temperature by spectroscopic and theoretical techniques. Moreover, the most probable excitations of possible forms of curcumin in different solvent media were investigated by time-dependent density functional theory. Our results indicated that photo-physical behaviors of these forms depend strongly on the solvent polarity. In order to investigate the interactional behaviors of various forms of curcumin, we used the concept of linear salvation energy relationship proposed by Kamlet and Taft. Furthermore, according to the obtained results, the excited state dipole moments of various forms of curcumin with different resonance structures are higher than those in the ground state that increase the probability of charge transfer mechanism. [ABSTRACT FROM AUTHOR]

Molecular surrounding environment is one of the important factors that can modify nonlinear properties of materials. For precise investigation, in this paper, single beam Z-scan technique was used for measuring the third order nonlinear responses of Basic Blue 55 molecules in different solvent media. Reverse saturable absorption and self-defocusing characteristics were found to be highly dependent on molecular surrounding media properties. Moreover, from these experimental results the contribution of various intermolecular interactions on the third order nonlinear responses of Basic blue 55 molecules was determined. Our results show that strong hydrogen bonds between dye molecules and their surrounding medium have dominant role in increasing the nonlinear coefficients. So, by a quantitative studying, the precise investigation of nonlinear responses of dye solutions will be facilitated. [ABSTRACT FROM AUTHOR]

• Chiral dopants modify physical properties of a nematic liquid crystal. • Iregular nonlinear optical behaviors were observed by doping chiral dopants. • High polarizability and Kerr constant were obtained for 4% of chiral dopants. Liquid crystals with high electro-optical responses play significant roles in optics and photonics. Providing a simple method for increasing the electro-optical behaviors of liquid crystals can be considered one of the most important and challenging research areas. In this work, left-handed chiral dopants and temperature effects on the electro-optical properties of pure and doped nematic liquid crystals with different percentages of chiral dopants were investigated. Despite decreasing the Kerr constant by increasing the percentage of chiral dopants, and temperature, the maximum values were observed for 4% of chiral dopants near the transition temperature. In this case, the value of Kerr constant is approximately 20 times that of a pure liquid crystal sample. This interesting result can be related to the changes in molecular polarizability due to molecular interactions. Hence, doped liquid crystals with high and controllable responses can be a good candidate for designing optoelectronic devices. [ABSTRACT FROM AUTHOR]

• There is linear relationship between order parameter and pitch length. • PSCLCs indicate a iregular transmission features. • NLCs play important roles on the PSCLs optical behaviors. Polymer stabilized cholesteric liquid crystals (PSCLCs) with unique characteristics play important roles in optics and photonics. In this case, temperature induced effects can modify their function in various phenomena. In this work, optical responses of PSCLCs were studied at different temperatures and temperature dependent properties of prepared PSCLC were successfully equationalized. According to the experimental results, there are good linear relationship between calculated pitch lengths and temperature. Moreover, the experimental results indicate that nematic liquid crystal (NLC) temperature dependent characteristics play important roles on the PSCLCs pitch length. In this case, quantitatively investigation of relationship between pitch length and LC order parameter provide new method for calculation of pitch length. Therefore, the calculation of pitch length based on NLC order parameter can facilitate the studies on PSCLCs. [ABSTRACT FROM AUTHOR]