Dispersion of refractive index and absorption coefficients in flux-grown high-resistivity KTiOPO4 crystals between 0.2-2.5 THz are verified at room temperature by a THz-TDS. Measured dispersion components n x, n y and n z are approximated for the first time in the form of Sellmeier equations. Phase matching for down-conversion into the THz range under a visible and near IR pump is found possible only in the principle XZ plane by s f → f and s f → f types of three-wave interactions. Low frequency THz generation is favorable due to the low absorption coefficient down to 0.2 cm-1, below 0.5 THz.
- nonlinear optical crystals
- phase matching