A study on the linear and nonlinear optical properties of Li and NH4 doped potassium pentaborate crystals

In this letter, we report on the linear and nonlinear optical investigations of 5 mol% of Li, NH4 doped potassium pentaborate (KB5) crystal. Doping concentration was quantified by the EDAX and ICP analysis. The enhancement of transparency in the doped crystals was recorded in UV-vis-NIR spectra. Optical band gap of the pure and doped crystals was also calculated. The optical nonlinearity of the grown crystals was confirmed by Second Harmonic Generation (SHG) test which shows that the dopants in the KB5 crystal enhanced the SHG efficiency of that material. The third order nonlinearity was studied by Z- scan technique using 632.8 nm He-Ne laser. The values of nonlinear absorption coefficient (β) and nonlinear refractive index (n2) were calculated. Third order nonlinear susceptibility (χ(3)) of the Li and NH4 doped crystals is 1.0278×10−3 esu and 0.7744×10−3 esu respectively which is higher than that of pure KB5 (0.6770×10−3 esu).