Irradiation Effect on Piezooptic Dispersion of Li2Ge7O15 Crystals

The ferroelectric single crystals Li2Ge7O15 (LGO) was irradiated by X-ray for one hour. The piezooptic dispersion of the ferroelectric crystal Li2Ge7O15 (both un-irradiated and irradiated) were studied in the visible region of the spectrum at room temperature (298 K). The results show an interesting photoelastic behavior. The piezooptic coefficient C decreases with wavelength in the visible region up to a certain wavelength and then it shows a peak at sodium yellow wavelength and later on the usual reduction is observed. Thus there seems an optical zone in between 5400 and 6200 with an enhanced piezooptical behavior. This enhancement is observed to be very high, as high as 50%, when the crystal (un-irradiated) is stressesd along [001] and observation made along [100]. The height of this region is different for different orientations, though the width seems approximately the same. The peak value increases about 25% when the crystal (irradiated) is stressed along [001] and observation made along [010] and that value decreases about 18% when the crystal (irradiated) is stressed along [001] and observation made along [100]. The height of the peak of this region remains almost same for all other orientation of the crystal (irradiated).