Résumé
We measure optically the increase of quadrupolar order ΔS, induced by a stabilizing electric field E, in the nematic liquid crystal 4'-n-pentyl-4-cyanobiphenyl with large positive dielectric anisotropy εa∼10. ΔS shows a linear and a quadratic dependence on E. Both effects are comparable for the largest field E∼3×105 V/cm. The linear variation is interpreted as originating from the quenching of macroscopic orientational fluctuations, while the quadratic contribution is a superposition of the microscopic Kerr effect and of a saturation term due to the macroscopic effect.