A new optical method for measuring the diameter of transparent filaments has been developed. It is based on determining the dimension of a sharp shadow image of the filament on a photo-detector. The influence of transmitted light is diminished by spatial filtering. The resolution is better than 1% for diameters down to 10 μm.
G. C. Dubbeldam,
"Laser Shadow Method For Measuring The Diameter Of A Transparent Filament", Proc. SPIE 0599, Optics in Engineering Measurement, (16 July 1986); doi: 10.1117/12.952402; https://doi.org/10.1117/12.952402