Diffraction

Diffraction is a remarkable manifestation of the wave nature of light and can be observed e.g. when ligh impacts on an opaque plate with periodically located holes. Light waves passing through the holes combine (interfere), which results in beautiful patterns on a screen, e.g. a wall, behind the plate. The finer are the holes or another structure on the plate, the larger is the diffraction pattern, and its size also grows with increasing wavelength. This can be seen in the third photograph that shows diffraction patterns created by two lasers with wavelengths of 532 and 650 nm and a two-dimensional grating. The second row of photos shows diffraction on one and two layers of a very fine canvas used for the screen printing technique. The pictures in the fourth row show diffraction on circular openings; the diameter grows from left to right. There is an additional fine structure in these patterns because there was not one, but many opening. In the 6th to 8th rows we can see diffraction on a thin fiber. If the fiber is not perpendicular to the laser beam, the outgoing light propagates along the envelope of a cone, and by meeting a plane wall it creates conic sections - here they are circles, ellipses, and hyperbolas. The bottom pictures show speckles that occur when many waves from a laser beam reflected on a rough surface interfere.