Sensitive remote electric field measurements using water vapor as a molecular probe

A number of molecular processes involving water molecules occur under the influence of electric fields and/or charges. This Letter demonstrates sensitive electric field detection as low as 5.6 V/mm via coherent anti-Stokes Raman scattering, with water molecules acting as probes. Absorption of one of the two incident laser beams by water molecules explains a decrease in the signal intensity with vapor pressure, suggesting that this method has the potential to enable electric field measurement even with an unknown density of water molecules.