Piezospectroscopic imaging with a tunable Fabry-Perot filter and Tikhonov reconstruction.

By combining two well-established techniques--multispectral imaging with a tunable filter and regularized data inversion--a fast and accurate method for measuring, at each pixel of a CCD array, the spectrum emitted by a radiating object is obtained. The method is demonstrated with ruby R(1)- and R(2)-line fluorescence, using a narrowband tilt-tunable Fabry-Perot interference filter for data acquisition. Since the data inversion problem is badly ill conditioned, regularization is essential to obtain meaningful results. The reconstruction is capable of a peak wavelength accuracy of 0.01 nm, sufficient to measure the small wavelength shifts encountered in rubylike materials due to changes in the local crystal lattice stress. Thus, the technique presents a novel approach to piezospectroscopic imaging and offers 2 to 3 orders of magnitude faster mapping of local stress than current techniques.