Measurement of enhanced radiation force on a parallel metallic-plate system in the microwave regime.

We measure the force exerted by microwave radiation on a centimeter-sized parallel-plate metallic resonant unit. By varying the ambient environment, we distinguish carefully between the direct radiation force and the indirect photothermal component. At the microwave resonance, the former is measured quantitatively to be 100 times larger than the conventional radiation force. Furthermore, the enhanced radiation force tends to increase the separation of the plates. Both the direction and the magnitude of the measured force agree well with numerical calculations.