Microwave emission and conductivity of two-color short pulse laser produced plasmas*

Laser plasmas in gases produced by intense, short pulses are sources of microwave and terahertz waves. The amplitude and spectrum of the low-frequency radiation may contain information about the plasma that is inaccessible by existing diagnostic techniques, however work is ongoing to understand the precise generation mechanisms that may connect the characteristics of the radiation to those of the plasma. To better understand the relationship, we present simultaneous measurements of the conductivity and microwave fields radiated by a plasma created using a two-color laser pulse, where the laser fundamental and second harmonic frequencies are coherently superimposed and their relative phase precisely controlled. The electric field waveform determined by the two-color relative phase changes the electron trajectories immediately following ionization, but it is unclear if that change of initial conditions influences the subsequent plasma density, size, or electron momentum transfer collision rate. Our findings enable assessment of the viability of the microwave radiation for use as a non-invasive diagnostic for laser plasmas that are compatible with few existing methods.