Observation of strong terahertz field-induced second harmonic generation in plasma filaments

We report the observation of terahertz field-induced second harmonic (TFISH) generation produced by directly mixing an optical probe beam onto femtosecond plasma filaments. The produced TFISH signal is spatially separated from the laser-induced supercontinuum by impinging on the plasma at a noncollinear angle. The conversion efficiency of the fundamental probe beam to its second harmonic (SH) beam is greater than 0.02%, which represents a record in optical probe to TFISH conversion efficiency that is nearly five orders of magnitude larger than previous experiments. We also present the terahertz (THz) spectral buildup of the source along the plasma filament and retrieve coherent terahertz signal measurements. This method of analysis has the potential to provide local electric field strength measurements inside of the filament. (c) 2022 Optica Publishing Group

Automated summary

We observed terahertz field-induced second harmonic (TFISH) generation by directly mixing an optical probe beam onto femtosecond plasma filaments. The TFISH signal is spatially separated from the laser-induced supercontinuum by impinging on the plasma at a noncollinear angle. The efficiency of converting the fundamental probe beam to its second harmonic beam is over 0.02%, representing a significant improvement compared to previous experiments. We also demonstrated the terahertz spectral buildup along the plasma filament and retrieved coherent terahertz signal measurements. This analysis method has the potential to measure local electric field strength inside the filament.