Diffraction pattern of a pen springHelen ButlerAward: Top 100
School: queensland academy for creative industries This image was produced by a green LED laser diffracting through a small steel spring taken from a ball point pen. The image was photographed on a mat screen six metres from the spring. Diffraction patterns are usually defined in terms of an aperture of a fixed shape. However, an opaque obstacle, such as the spring, will from the same diffraction pattern as an aperture of the same shape according to Babinet's principle. The pen spring, when viewed from the side, has a zig-zag pattern - the wires are angled in two different directions, both the same angle from the vertical axis but in different directions. This leads to a diffraction pattern comprised of two lines, each rotated the same amount in opposite directions from the vertical axis due to the angle of the spiral. It is therefore possible to measure the angle of the spiral from the angle between the two arms of the diffraction pattern by dividing it in half. The narrow double slit diffraction fringes evident in the pattern correspond to the wire diameter and single slit diffraction envelope corresponds to the coil separation/pitch. 
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