The theoretical basis of the physical mesomechanical approach of strength physics is described. Based on a fundamental principle of physics known as local symmetry, this approach is capable of describing deformation and fracture comprehensively, and applicable to any scale level. It is thus useful to describe strength physics at the nano/microscopic without relying on phenomenology. An optical interferometric technique capable of resolving displacement at sub-nanometer level is introduced. Being capable of quantitative measurement, this technique is useful for characterization of material strength at the nano/microscopic level.