Resonant four-wave frequency mixing in the cw regime in sodium vapor

An experimental investigation was made of resonant nonlinear four-wave frequency mixing processes involving cw laser radiation in sodium vapor. It was found that, in spite of an increase in absorption, the use of resonant atomic nonlinearities can substantially improve the frequency conversion efficiency in the cw regime. The results of the measurements were compared with the theoretical conclusions. Ultraviolet radiation was generated at the sum frequency (λ_s = 268 nm) with the proportionality factor C=W_s/W₁W₂W₃≈2W^–2