Microwave-to-optical frequency conversion based on the Lamb shift

We consider the microwave-to-optical frequency conversion based on the Lamb shift, fine structure and forbidden transitions. The theory of such a conversion is developed and the efficiency of the microwave-to-optical frequency conversion is calculated. We show that the ratio of the peak power of the induced optical emission to the power of the incident microwave, for a hydrogen atom, can reach 1000000.