Optical parametric amplification and oscillation assisted by   low-frequency stimulated emission
  Optical parametric amplification/oscillation provide a powerful tool for coherent light generation in spectral regions inaccessible to lasers. Parametric gain is based on a frequency {\it down-conversion} process, and thus it can not be realized for signal waves at a frequency $\omega_3$ {\it higher} than the frequency of the pump wave $\omega_1$. In this work we suggest a route toward the realization of {\it up-conversion} optical parametric amplification and oscillation, i.e. amplification of the signal wave by a coherent pump wave of lower frequency, assisted by stimulated emission of the auxiliary idler wave. When the signal field is resonated in an optical cavity, parametric oscillation is obtained. Design parameters for the observation of up-conversion optical parametric oscillation at $\lambda_3=465$ nm are given for a periodically-poled lithium-niobate (PPLN) crystal doped with Nd$^{3+}$ ions. 
Stefano Longhi
physics.optics