Reflected light microscopy captured this beautiful digital image that features a combination of salt crystals and cells on an electron microscope specimen grid. The display of color on the surface of the salt crystals is due to interference patterns from surface reflections.

Salt Crystals and Cells Specimen: Salt Crystals and Cells on EM Grid Technique: Reflected Light Microscopy

An important characteristic of light waves is their ability, under certain circumstances, to interfere with one another. Most people observe some type of optical interference every day, but do not realize what is occurring to produce this phenomenon. One of the best examples of interference is demonstrated by the light reflected from a film of oil floating on water. The dynamic interplay of colors derives from simultaneous reflection of light from both the inside and outside surfaces of the bubble.

The two surfaces are very close together (they are only a few micrometers thick) and light reflected from the inner surface interferes both constructively and destructively with light reflected from the outer surface. This is because light reflected from the inner surface of the bubble must travel further than light reflected from the outer surface. When the waves reflected from the inner and outer surface combine they will interfere with each other, removing or reinforcing some parts of white light by destructive or constructive interference. The result is a beautiful display of color. If the extra distance traveled by the inner light waves is exactly the wavelength of the outer light waves, then they will recombine constructively and bright colors of those wavelengths will be produced. In places where the waves are out of step, destructive interference will occur, canceling the reflected light (and the color).