Highly selective four-wave mixing of low-intensity radiation in a degenerate two-level atomic system

Quasi-degenerate four-wave mixing (FWM) of low-intensity radiation (with an intensity less than 1 mW cm(-2)) was observed for the 5S(1/2)(F = 2)- 5P(3 /2) (F' = 3) transition in an optically transparent Rb-87 vapour under cond itions of electromagnetically induced absorption. The efficiency of frequen cy conversion was no less than 1% with respect to the intensity of pump wav es. Nonlinear FWM is highly selective relative to the frequency detuning of pump waves (the FWM full width at half maximum was less than 50 kHz).