Abstract:
The presence of a Langmuir wave in an unmagnetized plasma is shown to allow parametric decay of
an electromagnetic wave into two electromagnetic waves, which is otherwise not allowed due to
wave number mismatch. The decay occurs at plasma densities below one ninth the critical density
and the decay waves propagate at finite angles to the pump laser. Above the threshold, the growth
rate scales linearly with the amplitude of the Langmuir wave and the amplitude of the pump
electromagnetic wave. The frequency x of the lower frequency decay wave increases with the angle
its propagation vector makes with that of the pump. The growth rate, however, decreases with x.
