Electric field polarity determination using amplitude and phase measurements of electric-field-induced second...

We demonstrate a technique that simultaneously determines electric field polarity and reconstructs its spatial profile by measuring both the phase and intensity of the electric-field-induced second-harmonic (E-FISH) signal. Although phase measurements using interferometric techniques have been proposed for polarity detection, the influence of the electric field's spatial profile on the E-FISH phase needs to be carefully considered. We show that electric fields with symmetric, even-function spatial distributions and the same polarity can produce a π-phase shift depending on their shape, indicating that phase information alone is insufficient and that intensity information must also be incorporated. By combining both phase and intensity, our method achieves accurate polarity identification and electric field profile reconstruction, with an accuracy of up to 91.3%.