Near field measurements of broadband radio frequency radiation generated from an ultrashort pulsed laser induced plasma in air

The emission of radio frequency (RF) signal from laser induced plasma is a phenomenon which has yet to be experimentally linked to a theoretical model. In an effort to support developing models behind the mechanisms responsible for these RF signals, experimentation was performed obtaining data in the near field surroundings (0.5 cm to 5 cm) of an Ultra Short Pulse Laser (USPL) generated plasma. The plasma was generated by an 800 nm, 50 fs USPL focused at 3 m. A D-dot probe measured the electric field of this plasma in an array of positions both longitudinally along and radially away from the plasma profile. Tests were performed at various energy levels ranging from 50 mJ to 200 mJ. Additionally, an RF horn capable of measuring between 1 GHz to 18 GHz was used to measure far field RF emissions. A microphone array was also implemented to examine the plasma’s acoustical profile. Current theory accounts for the RF emission through a surface wave mechanism driven by the constructive interference of electromagnetic waves near the plasma. Experimental results from the D-dot probe and microphone array were compared to this theoretical model.



DISTRIBUTION A: Approved for public release; distribution is unlimited. Public Affairs release approval #AFRL2023-3068