Investigation of Near Two-Photon Resonance Optical Nonlinearities in Ni(Ac)[sub 2][N-(8-Quinolyl) Pyridine-2-Carboxamide] · 4H[sub 2]O by the Z-Scan Technique.

We describe a modified Z-scan technique for the case when nonlinear refraction is accompanied by nonlinear absorption to separately evaluate the nonlinear refraction and the nonlinear absorption by performing straightforward measurements with the aperture removed. We divide the closed aperture (S < 1) normalized Z-scan by a scan with an open aperture (S = 1). With nanosecond scale at a 532 nm wavelength, we first measured the nonlinear optical absorption and refraction coefficients of a solution of Ni(Ac)[SUB2][N-(8-quinolyl) pyridine-2-carboxamide] 4H[SUB2]O by using the modified Z-scan technique. The nonlinear absorption originates from the near resonant two-photon absorption while the mechanism of the nonlinear refraction is the near resonant two-photon absorption transition enhancement. The linear increasing dependences of the optical nonlinearities on the incident irradiance arise from the population redistribution due to the near resonant two-photon absorption. [ABSTRACT FROM AUTHOR]