Imaging piezospectroscopy

A novel instrument is described for obtaining accurate high-resolution residual stress images of aluminum oxide materials, based on the piezospectroscopy of Cr(3+) dopant ions. The instrument employs a charge coupled device camera, a narrow bandpass tunable filter and the use of Tikhonov regularization for reconstruction of the raw spectral data. The experimental accuracy and spectral shift resolution of this method were analyzed with two calibration light sources and with independently measured spectra, and were found to be approximately +/-0.01 nm across the pixel array. This is close to the theoretically obtainable accuracy for the particular filter used, a solid etalon Fabry-Perot filter with a passband of 0.25 nm, based on an analysis with simulated data. The spectral resolution corresponds to a stress resolution, under biaxial stress conditions, of +/-40 MPa.