Sensitive detection of electric field-induced second harmonic signals.

We demonstrate sensitive electric field measurements by coherent homodyne amplification of the electric field induced second harmonic generation (E-FISH) technique. In the process of E-FISH, an applied electric field breaks the centrosymmetry of an otherwise homogeneous medium, in turn promoting the generation of the second harmonic frequency of an incident field. Due to weak third-order hyperpolarizability and the requirement of an applied field to break the symmetry, the E-FISH technique has been mainly used to study high fields, also requiring a strong optical field and sensitive detection.