ABSTRACT
This chapter is devoted to diffraction-based instrumentation, and starts with a description of Gaussian beams propagation, for designing alignment and level-check instruments for construction work, terrain leveling, and consumer applications. To check the beam spot position, photodiodes like quadrant photodiode and position-sensing are treated. By the diffraction pattern generated by a laser beam, a wire-diameter sensor is developed, and extended to measurement of diameter distribution, such as used in particle-size analyzers for industry and biology. Methods for inversion of scattering data to diameter distribution like LSM (least square method), iterative and Chahine's methods are discussed. In addition to the Low-Angle Elastic Light Scattering (LAELS), other kind of analysis are considered, like the Spectral Extinction Aerosol Sizing (SEAS) and the Dynamical Scattering Size Analyzer (DSSA), the base for covering the diameter measurement range 10 nm to 3 mm.
