Experimental observation of rainbow scattering by a coated cylinder: twin primary rainbows and thin-film interference

We experimentally examine the primary rainbow created by the illumination o f a coated cylinder. We present a simple technique for varying the coating thickness over a wide range of values, and we see evidence for two differen t scattering regimes. In one, where the coating thickness is large, twin ra inbows are produced. In the second, where the coating is thin enough to act as a thin film, a single rainbow is produced whose intensity varies period ically as the coating thickness varies. We find good agreement with previou s theoretical predictions. (C) 2001 Optical Society of America.