Evidence for the Role of Rotons in the Stimulated Emission of Phonons in Liquid 4He

When two high intensity pulses of excitations are injected into liquid 4He a strong non-linear interaction occurs which produces a large signal. We propose that rotons from the first pulse form relatively long lived surface rotons on the bolometer and these are stimulated to decay into phonons by rotons in the second pulse. The interaction signal is strongly dependent on the liquid 4He pressure and is αexp (-Δr(P)/kTe) which is evidence that rotons are involved.