The use of polarization in the piezospectroscopic determination of the residual stresses in polycrystalline alumina films

Experiments are described in which the R-line luminescence spectra from the thermally grown oxide formed by high temperature oxidation are recorded as a function of uniaxial strain and under different polarization conditions. The data obtained are used to calibrate both the piezospectroscopic effect and the effect of polarization when an external strain is superimposed upon a residual stress field. Although the incident polarization of the light used to excite the luminescence affects the total emission intensity, it does not affect the polarization of the luminescence signal. However, the ratio of the areas of the R2 and R1 luminescence peaks is dependent on both the stress and the orientation of the polarization of the optics used to collect the spectra relative to the applied stress direction. This provides the basis for determining the principal stress directions in a polycrystalline film. No effect of polarization was observed on the frequencies of the R2 and R1 lines.