Suppression of stimulated phonon emission in ruby by a magnetic-field gradient

It is demonstrated that a magnetic-field gradient can suppress amplified stimulated emission of phonons taking place within the Zeeman-split E-bar(²E) doublet of Cr³⁺ in 700 ppm ruby. The doublet is initially inverted by selective pulsed optical pumping. The field gradient produces a gradient in the transition frequency, thereby reducing the gain of the amplifying medium. The experiments are described with rate equations in which the gain is accounted for by the interaction length over which the phonons remain at resonance.