Third-order nonlinear optical response of magnesium sulfite hexahydrate

The third-order optical susceptibility of magnesium sulfite hexahydrate (MgSO₃.6H₂O) single crystal is experimentally studied by nonlinear laser spectroscopy. Third-harmonic generation (THG) and two-photon absorption (TPA) in this crystal are examined within the 600 - 1500 nm range by picosecond optical parametric oscillator (OPO). Some important characteristics of the crystal such as the THG efficiency, the value of the cubic susceptibility χ⁽³⁾, the dispersion of the third-order nonlinearity and the nonlinear refractive index (n₂), are determined.