Irradiation Effect on Piezooptic Dispersion of Li₂Ge₇O₁₅ Crystals

Abstract

The ferroelectric single crystals Li ₂ Ge ₇ O ₁₅ (LGO) was irradiated by X-ray for one hour. The piezooptic dispersion of the ferroelectric crystal Li ₂ Ge ₇ O ₁₅ (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_λ 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 Å and 6200 Å 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).

Keywords:

• Ferroelectrics
• optical properties
• X-irradiation
• nonlinear optics

Acknowledgment

One of the authors (A. K. B) is thankful to the Government of India for providing the research fellowship under Indian Council for Cultural Relations (ICCR).