Diffraction on a needle, Photo 1 of 2. A needle is placed in a beam produced by either a Helium-Neon laser operating at 632.8 nm (red, Photo 1) or a Helium-Neon laser operating at 543.4 nm (green, Photo 2). The resulting Fresnel diffraction patterns are observed at the same distance from the needle. Note that the fringe spacing is smaller for the green laser.