Enhanced third-order nonlinear optical properties of methyl orange dye-doped potassium penta borate octa hydrate (MOPPB) single crystals using CW diode laser for optical limiting applications

We report pure potassium penta borate octa hydrate (PPB) and methyl orange dye-doped potassium penta borate octa hydrate (MOPPB) for optical limiting applications. The crystals were grown by slow evaporation solution growth technique at ambient conditions. The single crystal X-ray diffraction (SXRD) evinces the orthorhombic class of the pristine and MOPPB crystals. Formation of PPB and incorporation of MO dye in PPB was confirmed through Fourier transform infrared (FTIR) study. Calculated hardness number and stiffness constant with Vicker’s Micro hardness study portrays the soft nature of the title crystals. The decrease in bandgap of MOPPB is due to the additional energy levels introduced between the valence band and conduction band which in turn increases the net polarizability of the crystal. Relative second harmonic generation (SHG) efficiency of pure PPB and MOPPB is 0.45 times and 0.40 times that of SHG output of KDP. Z-scan studies shows that both crystals show reverse saturable absorption (RSA) ascribed due to two-photon absorption (TPA) process. MOPPB [β = 1.68 × 10–5 m/W, n2 = 10.2 × 10–12 m2/W, χ(3) = 3.5 × 10–9 m2/V2] possess higher NLO coefficients than pure PPB [β = 0.98 × 10–5 m/W, n2 = 4.62 × 10–12 m2/W, χ(3) = 6.1 × 10–9 m2/V2] which assured the superiority of azo dye incorporation in PPB crystals. Pristine and MOPPB crystals depict the optical limiting (OL) behavior under continuous wave (CW) diode laser irradiation at 785 nm. Thus, the linear and nonlinear properties bestow the MOPPB single crystal as a versed material for OL devices used for the safeguard of optical components from laser damage.