Switching of the radiation frequency in a medium with a quadratic nonlinearity and an optical transistor based on this effect

It is shown that abrupt transfer of radiation power is possible from one frequency to another at the output of a medium with a quadratic nonlinearity when its input is subjected to a small signal at the doubled frequency and the intensity of the signal is altered slightly under phase-matched interaction conditions and also in the case of deviation from such conditions. It is shown that an optical transistor can be constructed on the basis of this effect and that a "giant gain" can be achieved for a weak alternating signal.