Test of the Effect of Edge Parameters on Small-Angle Fresnel Diffraction of Light at a Straight Edge

Abstract

Precision photometric measurements of the optical Fresnel diffraction pattern produced by a straight edge were made on eight edges of various materials and with various edge cross sections to ascertain the effect of these parameters on the pattern. For unpolarized light at a wavelength of 5461 Å, approximately 600 fringes were detected and measured in each pattern, and 800 fringes were detected in some of the patterns. The theoretical position of the geometric shadow (I/I₀ = 0.25) is verified to an angular accuracy of 1 × 10⁻⁴ deg. The light intensity distribution was scanned at a constant speed and detected by a 1P21 photomultiplier tube cooled to dry-ice temperature. The distance between the light source and the photometer was 52 m, and the edge was placed 20 m from the source. A simple technique for automatic compensation for fluctuations of the primary light source is also described. Accuracy of approximately 0.2% in the intensity measurements and of 0.03% in fringe position far from the shadow boundary is claimed. To within the accuracy of the experiment, the intensity distribution for all eight edges agreed throughout the complete pattern, but there is a slight variation in fringe position from the simple scalar theory.