In this work، the optical properties dependence of Multi-Walled Carbon Nanotubes (MWNT) on concentration was discussed. MWNT samples were prepared in polypyrrole by an electrochemical polymerization of monomers، in the presence of different concentrations of MWNTs، using Sodium Dodecyl-Benzen-Sulfonate (SDBS) as surfactant at room temperature. The nonlinear refractive and nonlinear absorbtion indices were measured using a low power CW laser beam operated at 532 nm using z-scan method. The results show that nonlinear refractive and nonlinear absorbtion indices tend to be increased with increasing the concentration of carbon nanotubes. Optical properties of carbone nanotubes indicate that they are good candidates for nonlinear optical devices.

Introduction: Polymer matrix composites have been thought as insulating materials.Recently, the electrical and optical properties of polymers have been extensively investigated.Polymeric materials with positive nonlinear refractive index are very important in optics.Changes of light-induced refractive index are commonly described by the relationship n=n0+n2I, where n0 is the linear refractive index, I is the intensity of the light and n2 is the nonlinear refractive index coefficient. This phenomenon have considerable effects on the propagation of electromagnetic waves through the medium, which leads to well known effects such as self focusing or defocusing, self phase modulation, self bending and so on.Aim: In this work the effect of RF plasma on the nonlinear optical parameters of red lake doped Polyvinyl Chloride (PVC) polymer film is studied experimentally. Positive nonlinear refractive index of red lake doped PVC and decreasing of this index after RF plasma treatment are two important and interesting phenomena.Materials and Methods: In this experiment red lake doped PVC films are exposed to low pressure RF plasma for 5 to 15 minutes. Different experiments are done to study the effect of RF plasma treatment on the nonlinear optical properties of red lake doped PVC film, include beam broadening measurement, optical limiting measurement and open and closed Zscan experiments.Results: By obtaining the beam profile propagated through treated samples, nonlinear refractive index of red lake doped PVC films is found to be positive. This magnitude is decreased due to plasma treatment. The optical limiting behavior of samples is investigated by measurement of transmission through the sample, which is remained unchanged in comparison with pristine sample. The third order nonlinearity of plasma treated samples is measured using Z-scan method. Experimental results show that real and imaginary parts of nonlinear susceptibility decrease with increasing the time of treatment.Conclusion: Effect of plasma treatment on the nonlinear optical properties of red lake doped commercial PVC film is studied which is a very common way to improve the surface characteristics of polymer films.The nonlinear refractive index and absorption coefficient of this material as well as its third order nonlinear susceptibility are changed where the linear optical parameters of this polymer are remaining unchanged.

In the Fourier domain optical coherence tomography, a picture of the optical thickness (multiplication of the refractive index n in physical thickness d) is obtained; e. g. for the retinal layers, it is used to diagnose many diseases throughout the hospitals in the country. In this work, we introduce a method for a discrete and simultaneous measurement of the refractive index and the physical thickness of multiple layers using Fourier domain optical coherence tomography, without additional information regarding the structure of the sample under investigation. In this method, the only input data are the spectrum of the FD-OCT system and the optical thickness of the sample layers (OPLs), asobtained from Fourier transform of interference spectrum. The results of simulation indicate that the accuracy of the extracted parameters depends on the difference in the refractive index of sample interfaces, because the more the difference in the refractive index, the more the optical reflection index. Furthermore, we show that the accuracy of the extracted parameters is influenced by the accuracy of measuring OPLs. So, we introduce a method to optimize the accuracy of parameters in spite of uncertainty in measuring OPLs. Simulation results show that for transparent biological samples merged into the aqueous media, if sample layers have a refractive index less than 1. 55, these parameters can be extracted with an error less than 0. 001.