Low temperature phase barium borate: A new optical limiter in continuous wave and nano pulsed regime

• Low temperature phase barium borate were prepared by hydrothermal technique.
• In ns laser regime, nonlinearity due to effective 2PA process was observed.
• Under CW laser excitation, material shows self-defocusing nonlinearity.
• γ-BBO exhibits better limiting behavior.

Low temperature phase barium borate was synthesized by hydrothermal method. XRD analysis confirms the formation of γ-BBO or hydrated barium polyborate (Ba3B6O9(OH)6) which crystallizes in monoclinic system in the P2/c space group. The molecular structure analysis shows the presence of dominant BO4 unit and the hydrated nature of material. γ-BBO exhibits sharp absorption edge at 202 nm and highly transparency in the UV–Visible–NIR region. The peak at 347 nm in the emission spectrum is due to the presence of self-trapped exciton. The third order nonlinear optical properties and limiting behavior of low temperature barium borate in both pulsed and continuous wave regime were studied. The effective 2PA absorption coefficient of γ-BBO under ns pulse excitation is estimated to be 0.38 × 10−10 m/W. The nonlinear absorption coefficient, refractive index and optical susceptibility of the material in cw regime were found to be in the order of 10−5 m W−1, 10−12 m2 W−1, 10−6 esu respectively. In both regimes, low temperature phase barium borate exhibits better optical limiting properties than high temperature phase β-BBO.