Abstract
For triple resonances into a spin multiplet of a dilute paramagnetic solid, when the spectroscopic bridge (SB) conditions are fulfilled, high-efficiency microwave frequency conversions [1], or phase sensitive amplifications [2] have recently been predicted. Unlike the optical case. [3]. the efficiency of these processes is expected to reach the maximum value, when the coherent mixing of the three quasimonochromatie fields (the parametric process) is negligible [4].