Indefinite permittivity in KTP single crystal at infrared frequency

摘要

The polarized reflectivity of potassium titanyl phosphate (KTiOPO _4, KTP) single crystal was measured in infrared frequency with the electronic field of the incident wave polarized parallel and perpendicular, respectively, to the c axis. The permittivity dispersions of KTP single crystal were obtained by the fitting of the reflectivity spectra. The permittivity dispersions indicate that KTP single crystal exhibits five frequency intervals where the crystal exhibits contrary signs between ε_⊥ and ε_(∥). This means, in these frequency intervals, the natural existing crystal exhibits the properties of an indefinite media which is based on the anisotropic lattice vibration. However, these lattice vibrations cause a large loss.