  Supercontinuum (SC) light source has advanced ultrafast laser spectroscopy in
condensed matter science, biology, physics, and chemistry. Compared to the
frequently used photonic crystal fibers and bulk materials, femtosecond laser
filamentation in gases is damage-immune for supercontinuum generation. A
bottleneck problem is the strong jitters from filament induced self-heating at
kHz repetition rate level. We demonstrate stable kHz supercontinuum generation
directly in air with multiple mJ level pulse energy. This is achieved by
applying an external DC electric field to the air plasma filament through the
effects of plasma wave guiding and Coulomb interaction. Both pointing and
intensity jitters of 1 kHz air filament induced SC light are reduced by more
than 2 fold. This offers the opportunities for stable intense SC generation and
other laser filament based applications in air.
