Ultra-high-bandwidth polarization interferometry and optimal quadratic phase detection

A novel homodyne interferometer and analysis method are described which use orthogonal polarization components to measure large rapid changes in interferometric phase, in quadrature, in the presence of strong time-dependent attenuation of the scene beam. This approach overcomes the major sources of error associated with homodyne interferometry (sensitivity nulls, ambiguity in the direction of phase change when passing through a sensitivity null, and intolerance to beam power variations) while maintaining its intrinsic simplicity and speed, enabling extremely high-bandwidth, high-dynamic range measurements limited only by available detector technology. Using this technique, electron density in a magnetized plasma shock was measured with unprecedented bandwidth and resolution, revealing short-timescale features not previously observed.