3/2 omega(0) radiation from the laser-driven two-plasmon decay instabilityin an inhomogeneous plasma

We present the results of the first reduced model simulations of the nonlin ear development of the two-plasmon decay instability in an inhomogeneous pl asma, including properties of the : harmonic emission. A sharp increase in radiation and Langmuir turbulence fluctuation levels occurs above a thresho ld laser intensity that depends on initial fluctuation levels. We study the competition between the linear propagation of Langmuir waves in the densit y gradient and the nonlinear saturation due to the Langmuir decay instabili ty. The secondary decay Langmuir waves can provide the dominant source of t he radiation and are essential to explain experiments.