Measurement of third order susceptibility by nonresonant nondegenerate four wave mixing in polymer embedded cadmium sulfide quantum dot systems

We report clear evidence of third order nonlinearity χ(3) in polymer embedded cadmium sulfide quantum dot system as a result of nonresonant nondegenerate four frequency mixing. We notice thickness dependent enhancement of nonlinear absorption with increase in incident intensity of light. Two pump beams (λ = 1064 nm) were oppositely directed into the sample and to receive phase conjugated signal, a probe beam was focused at the point of intersection on the sample. In the conditions satisfying self diffraction phenomena, we have measured change in refractive index as a function of incident power. We have observed very high value of third order susceptibility (χ(3) ∼ 10−7 e.s.u.) and predict figure of merit as high as ∼1.9 for the thinnest quantum dot sample (0.54 μm). Nonlinear susceptibility drops by nearly 10 times for the thickest sample (1.211 μm) due to considerable suppression in nonlinear absorption.