Measurement of Mechanical Deformations Induced by Enhanced Electromagnetic Stress on a Parallel Metallic-Plate System.

We measured the electromagnetic stress-induced local strain distribution on a centimeter-sized parallelplate metallic resonant unit illuminated with microwave radiation. Using a fiber interferometer, we found that the strain changes sign across the resonant unit, in agreement with theoretical predictions that the attractive electric and repulsive magnetic forces act at different locations. The enhancement of the corresponding maximum local electromagnetic stress is stronger than the enhancement of the net force, reaching a factor of > 600 compared to the ordinary radiation pressure.