Abstract

We introduce an index matching technique which exploits the waveguiding properties of sapphire fibers, reduces the stray light level, and allows for the enhancement of Raman scattering signal- noise ratio. Raman scattering of sapphire fibers was conducted at room temperature using the 476.5 argon laser line. Red shifts were observed under tensile stress for both A_1g and E_g phonon modes. The stress-induced Raman shifts for the A_1g modes are in good agreement with the theoretical calculations. The deformation potential constants used in these calculations were obtained from the literature of bulk sapphire measurement under compressive uniaxial stress. However, the E_g modes shift to lower energy much faster than the calculated values. The behavior of the E_g modes under tensile stress is not fully understood and may be due to the restricted dimension effects. Since the surface effects are 2-D, they should only influence the E_g modes. Tensile stress tends to stretch the surface and relax the surface compression. Thus, a larger red frequency shift of the phonon modes may be expected compared with the bulk samples.

© 1989 Optical Society of America