Development and experimental demonstration of negative first-order quasi-phase matching in a periodically poled...

We worked on a new scheme of quasi-phase matching (QPM) based on the negative first order of the spatial modulation of the sign of the second-order nonlinearity. Applying this scheme in the case of angular-QPM (AQPM) in a biaxial crystal reveals new directions of propagation for efficient parametric frequency conversion as well as "giant" spectral acceptances. The experimental validation is performed in a periodically poled rubidium-doped KTiOPO₄ biaxial crystal. This new approach naturally extends to other periodically poled uniaxial crystals such as periodically poled LiNbO₃.