Characterization of airborne fibers via Fraunhofer theory: Examination of the validity of Fraunhofer theory using the exact scattering theory MMP

Owing to the health hazard of respirable airborne fibers, there is great in terest in detectors able to monitor fibers online. This paper features such an optical fiber detector which is based on Fraunhofer theory for the esti mation of fiber size. Because Fraunhofer theory is not an exact theory and does not take into account the three-dimensional shape of fibers and their material properties, comparative computations with an exact theory, the mul tiple multipole method (MMP), a variant of the generalized multipole techni que, were performed. For small fiber diameters these simulations showed dif ferences between diffraction patterns calculated via Fraunhofer theory and scattering patterns computed with MMR The differences were strongly depende nt on the optical properties of the fiber material.