Abstract Tunable mid-infrared radiation in the range of 2. 06– 12\, m was generated in air via loosely focused two-color femtosecond laser pulses. The emission spectra and beam profiles confirm its origin as four-wave difference-frequency mixing in a low-density air plasma filament. Near phase-matching due to low air dispersion opens possibilities for efficient energy conversion at high powers.
Vaičaitis et al. (Wed,) studied this question.