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 $100\mathrm{V}/\mathrm{cm}$ in air with submillimeter spatial resolution governed by the confocal parameter and femtosecond temporal resolution governed by the laser-pulse duration.

• Received 11 April 2016

DOI:https://doi.org/10.1103/PhysRevApplied.7.024024