An investigation of subnanosecond switching of 119-microm radiation achieved by irradiating high-resistivity silicon wafers with 1.7-ns, 337-nm pulses from a nitrogen laser is presented. The experimental results are compared with a one-dimensional numerical multilayer model, which accounts for the generation, recombination, and diffusion of the free carriers and the resulting change of the far-infrared optical properties of the Si wafer.