Parametric amplification of acoustic surface waves on CdS

We report some experimental results on the parametric interaction of codirected s.a.w. in photoconducting CdS. This interaction takes place through the 2nd-order electric field associated with the bunching of carriers. Below threshold conditions, we directly observed both parametric attenuation and amplification with a 30 dB dynamic range. At the highest electric level of the pump available on our apparatus, 16 dBm, the parametric gain is about 10 dB. Beyond the threshold conditions, we observed only a parametric attenuation.