Ym. Golubev et Gr. Ershov, Zero-noise conversion of the carrier frequency in a resonant zero-inversion medium consisting of three-level atoms, J EXP TH PH, 91(5), 2000, pp. 952-956
It is demonstrated that a three-level medium can be used to convert the car
rier wave frequency without decreasing the signal/noise ratio. (C) 2000 MAI
K "Nauka/ Interperiodica".