A pointwise separation algorithm to separate plasma density and thickness in two-beam interferometry

The conventional two-beam interferometry adopts only one expression about plasma density and thickness because only fringe shift is recognized from the recorded fringes. Therefore, the prior hypotheses that the plasma is thickness-uniform or circular symmetry have to be introduced to separate them, which limits the applied range and accuracy of the conventional method. This paper found that the laser beam will be deflected if the thickness changes, leading the recorded fringes to be defocused. As a result, a new expression relying on recognizing the defocus parameter of the recorded fringes is derived, and a pointwise separation algorithm to separate density and thickness is proposed based on the two expressions. Compared to the conventional algorithms, the new algorithm requires no hypotheses and thus has a wider applied range.