Resonant Rayleigh scattering from excitons in CdxZn1−xTe:ZnTe quantum wells: measurement of homogeneous linewidths

The technique of resonant Rayleigh scattering is used to determine the homogeneous linewidth across the inhomogeneously broadened exciton resonance in a Cd_0.25Zn_0.75Te/ZnTe multiple quantum well structure. An order of magnitude increase of the Rayleigh scattering signal over background is observed on tuning a narrow-band laser through the exciton resonance at low temperatures. Spectral and temporal measurements show the effect to be a true scattering process rather than luminescence. The interface and alloy fluctuations in the quantum well give rise to spatial fluctuations in the dielectric response of the system while the large exciton resonance causes strong enhancement of scattering. The homogeneous linewidth was calculated across the exciton resonance. The technique is compared with the dephasing and hole-burning techniques more commonly used in homogeneous linewidth measurements.     

A Rapid Method for Determination of Changes in Shape of Comminuted Particles Using a Laser Diffractometer

The size distributions of carefully screened √2 size fractions of ground materials were determined using a Microtrac laser diffractometer. The size distributions were fitted to the empirical function P(x) = 1/[1 + (x₅₀/x)^λ] where P(x) is cumulative mass fraction less than Microtrac size, x. The standard deviation of λ for a 50 second test time was approximately 0.5, so that seventeen test times give a mean with an estimated error within ± 0.25 (95% confidence level). Values of λ were 5.44, 4.82, 4.40 for a coal ground under different conditions, indicating statistically different shape distributions; the average value for mica was 2.91 owing to the high aspect ratio of the particles. The ratio of x₅₀ to the geometric mean sieve size was 1.2 for the coal and 0.70 for mica.