Studies on natural and inducedbirefringence using white light interferometry

Abstract

The effect of thermal annealing on the birefringence of three transparent polymers: polystyrene, polypropylene and cellulose acetate is studied. Thermal annealing at temperatures 80, 60, 40 and 20OC for eachpolymer sampleis applied. The birefringence and its dispersion across the visible region of spectrum for each polymer sample are measured by using the polarized white light interference method. Also, two atomic parameters: the resonance wavelength and the oscillator parameters differenceare deduced. The results show that the magnitude of the linear birefringence and theoscillatorparameters difference decrease whilethe resonance wavelength increases with increasing the temperature of thermal annealing. An interpretation of the experimental results is presented.The birefringence and its dispersion across the visible region of spectrum forthepolymer samplesare measured by using the polarized white light interference method. The effect of stress due to bending on birefringence of a cellulose acetate sheet and it’s dispersion is studied. Bending effect at radii of curvature 0f 2, 3, 4.5, 5.5cm is applied.The results show that the magnitude of the linear birefringence increase with increasing the curvature. There is three techniques to measure birefringence from the bended sheet interferogram. The induced birefringence due to bending shows normal dispersion. Both effects of thermal annealing and bending produce permanent changes which are stored in the sample even if the effect is removed. Birefringence can completely be controlled by adjusting the temperature of thermal annealing or curvature of bending to, respectively, decrease or increase the birefringence. The relative error in finding the birefringence is 1*10-3.