Species-Independent Femtosecond Localized Electric Field Measurement

We present an optical measurement method using a femtosecond laser for nonintrusive measurements of electric field strength and orientation in virtually any gas or gas mixture via second-harmonic generation. This simple method takes advantage of the asymmetry in polarizability induced by an applied electric field, which enables the otherwise forbidden second-harmonic generation in any centrosymmetric or homogeneous media. The use of a femtosecond laser source permits high intensities without avalanche breakdown and leads to the measurement of electric field strength down to approximately 100 V/cm in air with submillimeter spatial resolution governed by the confocal parameter and femtosecond temporal resolution governed by the laser-pulse duration.