The use of a Shack–Hartmann wave front sensor for electron density characterization of high density plasmas

This article examines the use of a Shack–Hartmann wave front sensor to accurately measure the line-integrated electron density gradient formed in laser-produced and Z-pinch plasma experiments. The minimum discernable line-integrated density gradient is derived for the Shack–Hartmann wave front sensor, as well as its range of applicability. A laboratory comparison between a Shack–Hartmann wave front sensor and a Twyman–Green interferometer is also presented. For this comparison, a liquid-crystal spatial-light modulator is used to introduce a spatially varying phase onto both of the wave front sensors, simulating a phase profile that could occur when a probe passes through a plasma. The phase change measured by the Shack–Hartmann sensor is then compared directly with the Twyman–Green interferometer. In this article, the merits associated with the use of a Shack–Hartmann sensor are discussed. These include a wide dynamic range, high optical efficiency, broadband or low coherence length light capability, experimental simplicity, two-dimensional gradient determination, and multiplexing capability.