Crystallite-Size Distribution Signatures from Nonlinear Harmonic Spectral Data of Polycrystalline Materials

Abstract

There is a practical desire to characterize grain-size distribution in zinc-blend samples in-situ, instead of cross-sectioning a sample to view the microstructure under a microscope as is currently done, due to the significant affect of grain size on optical properties. This work discovered that high-frequency modulations on higher-order harmonic peaks generated from zinc-blend samples are unique to the set of grains traversed by the beam, not a result of random noise. From this fact, correlations between spectral modulations as the beam translated horizontally through the sample were calculated. However, a high level of noise in the correlations prevented precise grain size information from being obtained via this method. Finally, it was shown that peaks in the spectral modulation of a translated beam corresponded to individual grains. Modulation peak widths were therefore extracted and log-normal probability density functions were fit to histograms of the width size distributions. Average peak widths calculated from this method showed good correlation to the average grain sizes observed when the samples were cross-sectioned. Therefore, with sufficient calibration, this method shows much promise for determing grain size distribution in-situ from an input laser beam.