Determination of in-depth probe response function using spectral perturbation methods.

Two calibration methods, besides the conventional defocus method, have been presented to determine the in-depth probe response function (i.e., the function characterizing the spectral intensity distribution within the probe volume along the sample in-depth direction) in photostimulated spectroscopy. One method is based on “perturbing” the detected spectral probe of a selected band by varying the aperture of a confocal pinhole placed in the light path to the spectrometer; the other method is based on perturbing the spectral position of a selected band using an applied (equibiaxial) linear stress field, superimposed on the sample by means of a biaxial bending jig. Using the R1 band of a sapphire film, the validity of these two methods for determining the in-depth probe response function, and their reciprocal consistency are demonstrated. The calibration methods, which allow one to maintain unchanged the position of the focal plane within the sample, appear to work well for determining the in-depth probe response function of films, coatings, or highly transparent thin plates, where the laser probe size is close to the sample thickness, and thus, the defocus method is hardly applicable. [ABSTRACT FROM AUTHOR]