Origins of the Kerr Effect in Organic Materials: Correct Experimental Assessment by Z-Scan Method

As the demand for higher bandwidth telecommunication systems grows, new technological approaches for information and communication technologies are necessary. As the existing electro-optical telecommunication system is reaching its limits great attention is given to the possibility to implement an all-optical system. For such a system to be realized, one of the most essential aspects is nonlinear optical (NLO) materials that can mediate the interaction of photons. At this moment the main bottleneck for all-optical telecommunication system implementation is lack of materials with necessary NLO properties – a high Kerr and Two-photon absorption efficiency.

This work presents an outline for a correct approach to Kerr effect studies. A nonlinear optical property characterization of a wide spectrum of novel organic materials that have not been previously studied is presented in this work as well. By employing the Z-scan method with polarization-resolved and laser pulse repetition rate dependent measurements the thermo-optical effect was separated from the Kerr effect. At the same time polarization-resolved measurements allow to parcel out electronic and molecular reorientation contribution to the Kerr effect. A comparison of experimentally obtained Kerr coefficient values to values calculated by Gaussian 09 with inbuilt density functional theory model shows up a significant underestimation of effect by Quantum Chemical modelling. The magnitude of this discrepancy grows in correlation with the two-photon absorption cross-section.


  1. Separation of Kerr and thermo-optical contributions to refractive index changes by the Z-scan method can be done by polarisation and pulse repetition rate dependent measurements.
  2. To correctly separate the electronic and the nuclear contributions to the Kerr coefficient for organic chromophores dissolved in solvents polarisation-resolved measurements must be used.
  3. When using Quantum Chemical calculations for predicting Kerr effect values for organic chromophores, molecular reorientation contribution can be calculated accurately from values of linear polarizability while a significant error for electronic contribution arises due to disregard of two-photon contribution.