Determination of Photoelastic Constant Ratio of the Two Components in Ge_xSi_1-x/Si Superlattice

From the intensity ratio of the folded longitudinal acoustic phonons with re-spect to the longitudinal acoustic phonon in a Ge_0.51Si_0.49/Si superlattice (SL),we obtained a photoelastic constant. ratio of 6.6 for Ge_0.51Si_0.49 alloy with re-spect to Si in the SL at wavelength 5145Å, which is 2.6 times greater than that obtainedby He Phys.Rev. B39(1989) 5919 in a Ge_0.51Si_0.49/Si SL.