Polarimetric z‐Scan Study of Nonlinear Chirooptic Properties of Chiral Polyfluorene

Chiral photonics is an emerging field which deals with enantioselective light–matter interactions, offering numerous exciting applications. Two main approaches to enhancing enantioselective interactions are currently under extensive study: 1) structuring light itself, and 2) developing materials with gigantic optical activity. Both are required to realize the full potential of this emerging field. Here, the intensity‐dependent optical activity of a chiral polyfluorene film that has been studied by using open‐ and closed‐aperture z‐scan techniques with ∼775 nm and ∼160 fs laser pulses is reported. For a film of ∼20 μm thickness, the measured two‐photon absorption coefficients are 1.24 and 1.49 cm GW^‐1, respectively, and the nonlinear refractive indices are 8.74 × 10⁻⁵ and 1.38 × 10⁻⁴ cm² GW^‐1 for right and left circularly polarized laser beams, respectively. The nonlinear optical activity of pure, undoped polyfluorene is the highest reported so far.