Relaxation of impurities in a nonresonant field and phonon amplification

Abstract

It is shown that the distribution of weakly coupled impurities over the energy levels in a relatively weak field is altered substantially if the field frequency is in one of the absorption sidebands. Depending on the relationship between the impurity, field, and phonon frequencies, the impurity can be cooled or heated strongly, and the level population can also be inverted. If the field frequency is greater than the impurity frequency, then phonon magnification occurs at the difference frequency in a definite field range. Analogously, by inducing a decay into magnons by a longitudinal or transverse field, the impurity spin distribution in ferromagnets can be changed and magnon amplification obtained. Absorption of the nonresonant radiation is saturated as the field increases.