Disclosed herein is a method including: providing a light guiding arrangement (LGA) configured to redirect light, incident thereon in a direction perpendicular to an external surface of the sample, into or onto the sample, such that light impinges on an internal facet of the sample nominally normally thereto; generating a first incident light beam (LB), directed at the external surface normally thereto, and a second incident LB, parallel to the first incident LB and directed at the LGA; obtaining a first returned LB by reflection of the first incident LB off the external surface, and a second returned LB by redirection by the LGA of the second incident LB into or onto the sample, reflection thereof off the internal facet, and inverse redirection by the LGA; measuring an angular deviation between the returned LBs and deducing therefrom an actual inclination angle of the internal facet relative to the external surface.