Tree-wave mixing of ordinary and backward electromagnetic waves:   extraordinary transients
  Three-wave mixing of ordinary and backward electromagnetic waves in pulsed regime is investigated in the metamaterials, which enable co-existence and phase matching of such waves. It is shown that opposite direction of phase velocity and energy flux in backward waves gives rise to extraordinary transient processes in greatly enhanced optical parametric amplification and in frequency up or down shifting nonlinear reflectivity. The discovered transients resemble slowed response of an oscillator on pulsed excitation in the vicinity of its resonance 
Vitaly V. Slabko, Alexander K. Popov, Viktor A. Tkachenko, and Sergey   A. Myslivets
physics.optics