A new approximation and a new measurable constraint for slab profile inversion

A new approximation and a new measurable constraint for slab profile inversion is introduced. A comparison is given between the Born, the exact, and the new approximation. The new approximation and constraint can be utilized along with other methods such as the integral equation, the iterative or perturbed Born, and the alternating projection approaches. The latter is considered. The results obtained are superior to those obtained under the Born approximation.