| Abstract: | This paper reports on the applicability and the limitations of reticles as standards in laser diffraction spectroscopy. In comparison with standard materials, reticles carry some advantages with respect to their ease of handling. In contrast, the static features on a reticle cannot faultlessly simulate a real measurement on a moving particle system. The difference becomes visible in the form of speckles superimposed on the diffraction pattern and is dependent on the positions of the features on the reticle. As long as the feature positions are random, the speckles are also randomly distributed over the pattern and the measurement data averaging the intensities over the detector ring areas are only slightly disturbed. However, reticles containing only non-overlapping features contravene the requirement of complete feature position randomness and their diffraction patterns show a dark ring close to the center. The normal evaluation of these diffraction patterns delivers size distributions which are too narrow and shifted to smaller particle sizes. Nevertheless, by defining a reticle specific phase function and by implementing it in the evaluation algorithm, the correct particle size distribution is obtained. Simulations have been performed to investigate reticles with and without overlapping features. |
