Parametric Decay of Obliquely Incident Radiation

An electromagnetic wave obliquely incident on an inhomogeneous plasma has a resonance near ${\omega }_0={\omega }_{\mathrm{pe}}\mathrm{}\left(x\right)\mathrm{}$. It is shown that temporally growing modes exist for parametric decay into ion-acoustic and electron-plasma waves in the vicinity of this resonance in spite of the density gradient. For typical laser fusion parameters the maximum growth rate is comparable to the ion-acoustic frequency. The mechanism can contribute to significant power absorption.