Isopachic method with unpolarized light

An isopachic method with unpolarized light using a Mach–Zehnder interferometer is proposed. In the case of unpolarized light, isopachics are observed not only due to a change in the thickness of the model but also due to induced birefringence. In contrast to the existing methods, the proposed method allows you to study sections of three-dimensional models or flat stressed samples with no thickness variation. A brief theoretical consideration based on the formalism of the coherence matrix is given, as well as the experimentally obtained isopachic field for a model made from high-modulus material. The method is convenient and simple in technical implementation.