Diffraction on a slit, Photo 2 of 3. A narrow slit is placed in the path of a laser beam and the resulting diffraction pattern is observed some distance away. In this series the camera to slit distance is fixed. Photo 1 and Photo 2 use two different Helium-Neon lasers, red (632.8 nm) and green (543.4 nm), illuminating the same slit. Note the extent of the pattern and the fringe spacing are smaller for shorter wavelength. Photo 3 uses the same red laser as Photo 1, but the slit width is narrower. Note the wider pattern and the increased fringe spacing in Photo 3 compared to Photo 1. Also note that in all photos the central lobe is oversaturated that allows to see the outer structure more prominently. This is a classic demonstration of the wave nature of the light.