Counter-propagating parametric interaction with phonon-polaritons in periodically poled KTiOPO₄.

Strongly enhanced backward stimulated polariton scattering (BSPS) is demonstrated in periodically-poled KTiOPO₄ (KTP) crystals with a high power-conversion efficiency up to 70%. We study the physical mechanism of such counter-propagating parametric interaction with phonon-polaritons in χ⁽²⁾ modulated structures. BSPS is a three-wave mixing that is distinguished from backward stimulated Raman scattering (BSRS), while a strong absorption at large polariton wave-vectors can still make BSPS display certain characteristics of BSRS such as self-compression of the Stokes pulse. We also compare BSPS with counter-propagating parametric oscillation in the near- and mid-infrared range, providing an estimation of the fabrication error margin to expect the outcome of their competition in the same device.