Innovative schemes for satisfying phase-matched and phase-corrected terahertz electro-optic sampling within intrinsically anisotropic non-centrosymmetric crystals

Abstract We report on electro-optic (EO) sampling of terahertz (THz) electric fields using non-centrosymmetric crystals that exhibit anisotropy even in the absence of an external electric field. Such anisotropic EO sampling crystals follow different optical dynamics than EO sampling crystals that are isotropic in the absence of an external electric field, resulting in a departure from the standard phase-matching condition used to describe THz EO sampling. Given these anisotropic EO sampling crystals, we recognize the need for electric field phase-correction and offer different approaches to achieve phase-correction. The theoretical conditions describing perfect phase-matching and perfect phase-correction are derived then experimentally validated for a representative AgGaSe₂ EO sampling crystal. This work offers a treatment methodology for detailing phase-corrected THz EO sampling within anisotropic non-centrosymmetric crystals, broadening the applicability of THz detection in complex media.