Nonlinear Model for Start-Up Phase Pressure Perturbation Spectra from Time-Dependent Optically Smoothed ISI Laser Imprint

The spectrum of early time pressure perturbations, due to optically smoothed induced spatial incoherence (ISI) laser imprint, is computed for a planar target using a forced, dissipative model. The ISI laser deposition is computed using a time-dependent electromagnetic full wave Maxwell code. We find that the pressure spectrum evolves into a power law in which spectral power is transferred from large to smaller scales through a nonlinear cascade process. A nonlinear analytical model is also developed and compared with simulations using the forced, dissipative model. We also compare the model predictions with experimental observations.