Determination of optical nonlinearities in Cu(mpo)2 by Z-scan technique

The optical nonlinearities of Cu(mpo)(2) [formula=C10H8N2CuO2S2] complex have firstly been investigated by using the Z-scan technique with a nanosecond-pulsed Nd:YAG laser at its second harmonic (532 nm) radiation. The nonlinear optical absorption and refraction coefficients of Cu(mpo)(2) have been measured with the different on-axial peak irradiances I-0 at the waist ranging from 0.48 to 5.66 GW/cm(2). The nonlinear transmittance characteristics exhibit the near resonant two-photon absorption (TPA) at 532 nm and are explained by a population redistribution model. The nonlinear absorption originates from the near resonant TPA while the mechanism of the nonlinear refraction is the near resonant TPA transition enhancement. The linear increasing dependences of the optical nonlinearities on the incident irradiance arise from the population redistribution due to the near resonant TPA.