Distributed feedback of a thin‐film optical guided mode has been produced by a periodic perturbation of the guide height. Using photoresist and ion‐milling techniques, gratings with a period of ∼0.2 &mgr; and a peak‐to‐peak height of ∼0.1 &mgr; have been formed on fused silica substrates. A film of polyurethane doped with Rhodamine 6G pumped by an N2laser formed the gain medium. Data presented on the oscillation threshold of several lasers are in agreement with calculated feedback parameters. This technique is capable of producing high‐resolution gratings in durable materials which can provide feedback in low‐gain laser media.