Fig. 1
The THz-induced Kerr effect in water and reference liquids. The refinement (red curve) is the sum of two contributions: An instantaneous electronic birefringence (orange curve) and a delayed, molecular birefringence (purple curve). While in the non-polar molecules carbon disulfide (CS2) and benzene (a, b), a positive molecular alignment effect is observed together with a positive electronic response, the polar water molecules in regular (H2O; c) and heavy (D2O; d) water as well as aqueous solutions of sodium iodide (NaI; e, f) reveal a negative molecular orientation effect. The electronic Kerr effect background of the cuvette was subtracted. We also isolate the molecular orientation mechanism of water based on its temperature dependence \(- {\rm{d}}\Delta \phi /{\rm{d}}T\) (purple curve) in a background-free measurement. Error bars correspond to the standard deviation. In c, d, additional dotted curves, offset by −0.03 mrad, correspond to a convolution with a Gaussian σ = 1.4 ps. Error bars represent the standard deviation
