GB1523604A - Method of measuring the roughness of a surface - Google Patents

Abstract

1523604 Photo-electric measurement of roughners SVENSKA TRAFORSKNINGSINSTITUTET 5 Aug 1975 [5 Aug 1974] 32712/75 Heading G1A The roughness of a surface is measured by illuminating it with a parallel light beam at a given angle of incidence and determining (a) the amount of light reflected at an angle equal to the angle of incidence, or (b) the amount of light which is polarized perpendicular to the plane of incidence and which is reflected at an angle equal to the angle of incidence, and (c) the amount of reflected light which is polarized parallel to the plane of incidence; the roughness is found from the ratio of (a) or (b) to (c). In Fig 1 the surface 1 of a sheet of paper to be investigated is illuminated with a laser beam, which may be polarized. Light reflected at the angle of incidence, which is preferably within 10 degrees of Brewsters angle, passes to photodiode 4 via a polarizer 3. This polarizer is moved to and fro so as to select alternately the polarized light (c) above, and either all light or light polarized normal to the incidence plane depending on whether circuit 6 is to form the ratio with signal (a) or with (b). A polarizing beam-splitter may be used with two photodiodes to produce signals (b) and (c), Fig. 2 (not shown), or two photodiodes and polarizers may be used to produce these signals, with (c) being measured at an angle other than the angle of incidence, Fig. 3 (not shown).