Optical dephasing of neat liquids and liquid crystals studied by forced light scattering

The dephasing of induced dipole moments in neat liquids is studied for the first time. The use of incoherent light instead of single femtosecond pulses is essential in the forced light scattering experiment to obtain the required pulse repetition rate. The data can be described by an effective inhomogeneous broadening. Neat solvents showed a linewidth ΔG ≈ 66 THz. Isotropic as well as nematic phase 4-n-pentyl-4′-cyanobiphenyl (5CB) has a reduced linewidth (ΔG ≈ 50 THz) as a result of increased ordering. The effective inhomogeneous broadening for the electronic transition of the dye all-trans-β-carotene dissolved in cyclohexane is the same as for the neat solvent. The higher dynamic range in the dye experiment favours a Kubo model (ΔK = 50 THz, τc = 37 fs) rather than an effective inhomogeneous broadening.