Extraordinary time-depended processes in the parametric interaction of counter-propagating waves

Three-wave mixing of ordinary and backward electromagnetic waves in the pulsed regime is investigated. It is shown that opposite direction of phase velocity and energy flux in the backward wave gives rise to extraordinary transient processes in the greatly enhanced optical parametric amplification and frequency-shifting nonlinear reflectivity. The discovered transients resemble time-delayed response of an oscillator on the pulsed excitation in the vicinity of its resonance.