Characterisation of the intensity dependent refractive index of nonlinear polymers in solution

Abstract

Polymers form, besides semiconductors, a class of interesting optically nonlinear (ONL) materials. The nonresonant nonlinearity of π-conjugated polymer systems can be relatively large and the nonlinear response time is often in the ps-regime, even in the resonant case. We use a Fabry-Perot to determine both the real and imaginary part of the intensity dependent refractive index of ONL polymers in solution. The etalon converts changes in the refractive index and absorption coefficient of the material inside the resonator (the polymer solution) into a transmission change.1 It is useful to characterise the nonlinearity of the material in solution as it may be difficult to grow crystals or spin waveguides of newly developed nonlinear polymer systems. The Fabry-Perot is inserted in a pump-probe type setup, as shown in Fig. 1. The change of the optical parameters is induced by a 527-nm 35-ps pump pulse and detected with a 660-nm 5-ps probe pulse.