An optical film having structures that vary in height along their length where the variations have a nominal period of less than forty times the nominal height of the structures is taught. Also provided is a process for reducing electrostatic charge in the production of polyolefins by introducing dinitrogen monoxide into the polymerization medium. Thereby, the flatness of the surface of the silicon oxide film embedded within the isolation groove can be improved over the entire part of the dummy region FA. The process provides both Methane and carbon di oxide conversion more than 90% without any noticeable deactivation till 100 hours between temperature range of 500-800\xb0 C. A stem extends from an end of the first armthe second arm.