I. SEMICONDUCTOR MATERIAL HIGH RESISTIVITYA was grown by the float-zone technique. Its long carrier lifetime ( T > s) enabled it to obtain a high electron-hole plasma density at moderate illumination levels. A 75"-diameter, 1.9-mm-thick slab was cut from the ingot. To decrease surface recombination, both of the flat sides of the slab were finished by chemical-mechanical polishing.
EXPERIMENTAL SETUPTo produce a nonequilibrium plasma, we illuminated the slab with a pulsed xenon lamp through a grating mask (Fig. l), fabricated by printing opaque strips on transparent film, and .entirely transparent to MMW. The incident MMW beam was formed by a horn antenna. The combination of the MMW frequency, 92 GH7, the refractive index of silicon, 3.45, and the slab thickness, 1.9 mm, satisfied the conditions for suppressing Fresnel reflection at normal incidence. The MMW beam that passed through the silicon slab was detected by a GaAs Schottky diode coupled with a second horn antenna. The detector was mounted on a rotating arm to measure the angular distribution of the diffracted beam. The pumping light pulses were monitored using a reference photodiode that detected pumping light reflected from the slab. Both the rectified signal
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