The performance characteristics of small‐period electromagnet wigglers of novel design are measured and compared with theoretical expectations. Field measurements for wigglers driven by dc, ac, and short‐pulse current sources are reported. Fields as high as 1 kG have been readily obtained in a double‐sided 3.9‐mm‐period wiggler. These performance capabilities allow the design of high‐power free electron laser oscillators and ‘‘optical klystron’’ amplifiers in the near‐millimeter regime using modest electron beam energies in the range 200–400 keV. Oscillator and amplifier designs for operation at 150 and 300 GHz are presented. The generation of 1.2 MW of 150‐GHz radiation with >50% efficiency is predicted.