A reflecting device of unique characteristics is demonstrated. It is based on a combination of two effects: frustrated total internal reflection and wavefront interference. The device modifies its spatial reflectivity as a function of frequency in a very sensitive way. Experiments showed power reflection changes of 50% within a range of 3 GHz. The device is implemented as an output mirror in a pulsed Nd:YAG laser and significant improvement in the optical quality of the generated beam is observed.