Submillimeter-wave generation by difference-frequency mixing of ruby laser lines in ZnTe

A submillimeter wave of 0.34-mm wavelength with peak power of ∼10
^-3
watt has been generated in ZnTe by beating the R
1
and R
2
lines of a
Q
-switched ruby laser. As the detector
n
-InSb cooled to 1.7°K was used. The dependence of the beat power upon the angle between incident electric fields and the crystallographic axis was in accordance with the
43m
symmetry. The observed beat power was smaller, by three orders of magnitude, than the calculated one based on the assumption of collinear plane waves. A theory including the effect of input beam divergence inside the crystal gives a beat power fairly close to the measured value. Some results of auxiliary experiments supporting our viewpoint are also given.