The many uses of insects

Michael Berry points out a pretty unexpected & neat application of physics.

In one of his lovely films, David Attenborough showed insects floating on a sunlit pond, and pointed out their curious shadows: unlike more familiar shadows, these underwater ones have bright edges. The reason is that surface tension bends the water near where the insects float, and the light is sharply focused by these curved surfaces. This prompted a systematic study of bright shadows, including the similar ones cast on the bottoms of rivers by little whirlpools on the surface. In these shadows, the light focuses onto a ring. That was in 1983.

The paper was noticed by Michael Gorman, a physicist at Houston. It inspired him to make a plastic lens of unusual shape, whose function is to mimic whirlpools with their ring focusing. He surprised me by announcing that he had patented this construction with the hope of profiting from it. For example, angioplastic surgeons were interested in shining a powerful laser through a tiny version of the lens, at the end of an optical fibre, and with the ring focus bore holes through blocked arteries. (At my time of life, this application is close to my heart.)