Ultrabroadband Mid-Infrared Supercontinuum Generation at 5 kHz by Electric Field Assisted Two-Color Filamentation in Air

We demonstrate the stabilization of mid-infrared (MIR) supercontinuum pulses generated by two-color filamentation through the application of a static DC electric field. By applying a strong electric field to the laser filament using a Rogowski electrode, we observed significant improvements in both pulse intensity and pointing stability at high positive voltages. Specifically, the instability of the intensity was reduced from $\sim$3.5% to $\sim$1.3%, while the instability of the beam pointing along the vertical axis – the direction of the applied field – was also reduced from $\sim$0.020 mrad to $\sim$0.005 mrad. These enhancements are attributed to the spatial separation of ions and electrons within the plasma, which suppresses recombination and subsequent thermal-induced refractive index fluctuations. The improved pulse characteristics were successfully inherited by upconverted MIR spectra, with the integrated spectral stability improving from $\sim$6.0% to $\sim$3.3%. Finally, we demonstrate that these stabilized pulses greatly suppress noise in MIR hyperspectral imaging via sum-frequency generation in a thin GaSe film, resulting in significantly enhanced image quality.