Broadband Microwave Emission from Laser Plasmas Generated in Water Droplets

A high-power ultrashort laser pulse focused in air generates a plasma that radiates broadband electromagnetic waves. The transient current source responsible for the radiation remains an open area of study. A laser plasma is generated in the presence of water droplets produced by a humidifier to investigate the physics governing the amplification of radiation at microwave frequencies in comparison to radiation quantities created by laser plasmas generated in air. A microwave horn is used to measure the radial pattern of radio frequencies (RF) from 2 to 13.6 GHz produced by the laser plasma. The extinction coefficient of the water vapor-based fog is determined by the transmittance of continuous wave lasers through the interaction region. Our research demonstrates a relationship between the density of the water droplets and the laser plasma radiation mechanism.