Light Amplification in a Thin Film

Abstract
Light amplification at 6328 Å in a rhodamine‐B‐doped polyurethane thin film is observed. The light‐guiding thin film is pumped transversely with a nitrogen laser. Superradiant light of the dye‐doped film is observed to be guided by the thin film. When a He–Ne light at 6328 Å is coupled into the same thin film along the same path, amplification results. Maximum unsaturated gain on the order of 13 cm−1 was experimentally determined by two different methods in a single‐mode thin‐film light guide with a concentration of 3.3×10−2 mol/liter when wet.