Diffraction on a slit. A narrow slit is placed in the path of a laser beam and the resulting diffraction pattern is observed some distance away. Two different Helium-Neon lasers, red (632.8 nm) and green (543.4 nm), are used to illuminate the same slit and the camera to slit distance is fixed. Note the extent of the pattern and the fringe spacing are smaller for shorter wavelength. Also note that in both cases 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.