  Accurate knowledge of absorption coefficient of a sample is a prerequisite
for measuring the third order optical nonlinearity of materials, which can be a
serious limitation for unknown samples. We introduce a method, which measures
both the absorption coefficient and the third order optical nonlinearity of
materials with high sensitivity in a single experimental arrangement. We use a
dual-beam pump-probe experiment and conventional single-beam z-scan under
different conditions to achieve this goal. We also demonstrate a
counterintuitive coupling of the non-interacting probe-beam with the pump-beam
in pump-probe z-scan experiment.
