Adequate laser focusing and signal acquisition conditions for 3D measurement of electric-field distribution by the E-FISHG method

Electric field measurement using electric-field-induced second-harmonic generation (E-FISHG) has attracted attention because of its non-invasiveness and high spatiotemporal resolution. In the electric field measurement by the E-FISHG method, the applied electric-field profile along the laser path outside the focal spot affects the SHG signal. We have proposed a method of calibrating and inferring the applied electric-field profile from the SHG distribution along the laser path. In our previous research, the successful inference of a relatively simple electric-field profile from a series of SHG signals was demonstrated. To measure more complex electric-field profiles, we apply our method to three cases of electric-field profiles: (1) the profile with different sharpness, (2) the profile with two peaks, and (3) the profile with noise superimposed on the SHG signal. The applied electric-field distribution can be inferred within 10% error by adequately choosing the confocal parameter. We also provide guidelines for the required signal acquisition region and measurement pitch when the approximate shape of the applied electric field is known, which are important for actual measurement.