Third Order Optical Nonlinearity with Far Field Diffraction Rings

Abstract

An experimental work has been done to study the third order optical nonlinearity of 2,5- dimethylaniline (DMA). The nonlinear phase shift and the nonlinear refractive index of DMA were estimated using the Far Field Diffraction Ring Technique. Due to the low transparency of DMA, it was dissolved in methanol. The nonlinear refractive index of DMA was measured for five different concentrations (V/V) of DMA dissolved in methanol using the Far Field Diffraction Ring Technique. Three different wavelengths 457 nm, 488 nm and 514 nm of a continuous wave (CW) Ar-ion laser were used with varying incident powers. The nonlinear phase shift of 2, 5- dimethylaniline (DMA) was calculated, counting the number of diffraction rings in the far field region. The number of diffraction rings depends on the incident laser power, sample concentration, distance of the sample from the lens, and the wavelength of the laser beam. The number of diffraction rings increases with increasing laser power and is the highest for the most intense laser power, for all three wavelengths. The number of diffraction rings is also highest for the highest sample concentration (V/V) for the same experimental settings. It is also found that the number of diffraction rings increases with the distance of the sample from a biconvex lens and the diffraction rings are highest at the focal plane of the biconvex lens used in the experiment. The above observations are true for all three laser wavelengths (457 nm, 488 nm and 514 nm) and among the three laser wavelengths; diffraction rings were highest for the laser wavelength 514 nm for the same experimental condition. The nonlinear phase shift of DMA was found to be negative for all five concentrations (V/V) and all three wavelengths, which indicates that the sign of the optical nonlinearity for DMA is negative. The measured order of the nonlinear refractive index, using the Far Field Diffraction Ring Technique, is found to be the order of 10-6cm2/W.