الفهرس 
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Abstract
This thesis presents an experimental investigation of the nonlinear optical properties of novel nonlinear optical materials at wide spectral regions of the electromagnetic spectrum from visible to near infrared. Using Z-scan technique, nonlinear optical parameters of solvent (water) and rhodamine 6G dissolved in water have been investigated. The study was done by using femtosecond laser (100 fs) with high repetition rate (80 MHz) in a broad range of wavelengths from 730 nm to 850 nm and at different excitation average power starting from 0.6 W to 1.6 W. The obtained results showed that there is no nonlinearity of water observed at low average powers whatever the wavelength of excitation. But water showed saturable absorption at high laser average powers. The nonlinear absorption coefficient of water was found to be depend on both laser wavelength and incident power.
A transition from saturable absorption to reverse saturable absorption was observed when rhodamine 6G was added to the water. Reverse saturable absorption is related to the existence of two photon absorption in the solution which was sensitive to excitation wavelength, average power even at low powers and rhodamine 6G concentration. The two photon absorption cross section of rhodamine 6G solution was estimated from the nonlinear absorption coefficient and was found to increase with increasing excitation wavelength while decrease with increasing laser average power. It reaches to 666 GM at wavelength of 850 nm which is the highest value ever reported for rhodamine 6G. The obtained results showed that the rhodamine6G solution exhibits a negative nonlinear refractive index that is induced by self-defocusing. A clear increase in the nonlinear refractive index of rhodamine 6G solution has been found with the increase in the concentration of rhodamine 6G in water.
Finally, I-scan technique have been used for the optical limiting study of rhodamine 6G in high power femtosecond laser pulses at constant wavelength of 800 nm. The results shows that rhodamine 6G solution is a good optical limiter and its optical limiting behavior is concentration dependent. The higher concentration of rhodamine 6G solution has better optical limiting characteristics.