Conical four-wave mixing in sodium vapour excited by femtosecond laser pulses

Abstract

Broadband (sometimes exceeding 1500 cm-1) red-shifted (with respect to the sodium 3S–3P transition frequency) conical emission has been observed with the pump wavelength tuned in the range between 540 and 589 nm. Such broadband emission was attributed to the generation and amplification of light at the Rabi sideband frequencies in the field of intense femtosecond laser pulses. It has been shown that the cone angle of the emitted radiation is determined by the process of four-wave mixing under the conditions of longitudinal (Cherenkov-type) phase matching.