Microwave interactions with laser-generated air plasma filaments and acoustic shocks

We present recent NRL experiments that show long-lived (∼20 microseconds), efficient microwave reflection from an intense laser-air interaction region. This phenomenon is distinct from the short-lived response (∼10ns) that is typically observed for laser-produced air-plasmas and represents a thousand-fold increase in the duration of the reflection. Analysis suggests that the intense laser creates a fully ionized (1019 cm−3), high temperature (∼eV) plasma region in air. Long after the laser pulse has left, the region expands hydrodynamically while maintaining a sufficiently high plasma density (>1013 cm−3) to reflect incoming microwave radiation. To inform the ongoing experiments, we simulate the dynamics of laser-generated air plasmas using the SPARC simulation developed at NRL. SPARC is a three-dimensional, multi-species hydrodynamic simulation with user-defined rate law kinetics. The simulations capture the evolution of the air-plasma and shock waves in the presence of a high-power microwave field.