Experiments have shown that a single 10-μm-radius laser spot is not able to produce the 90° side-emitted 3/2 harmonic efficiently in a preformed laser plasma. However, with the help of one or two auxiliary laser spots with a size similar to that of the main spot, the side-emitted 3/2 harmonic can frequently be detected when some positional and angular conditions for the auxiliary spots are met. The origin of these phenomena has been analyzed in terms of a proposed reflected laser photon-coupling model.

• Received 29 October 1991

DOI:https://doi.org/10.1103/PhysRevA.46.5123