The Edge of the Rainbow

Ordinary light is made up of light of many different colors. You can see these colors if you bounce the light of a thin film on a highly reflective surface. Oil slicks show this effect where you see a whole spectrum of colors that result from the light reflecting of the surface of the oil and whatever is underneath.

Here, a thin polymer film is receding across a highly reflective silicon substrate leaving behind small droplets in its wake. The different colors tell you the thickness of the film; and, as you can see, it changes as you go across the film. The droplets form because the polymer doesn't like the surface and tries to bead up, just like water on a nonstick pan.

Irene Tsai, University of Massachusetts Amherst