The invention relates to a system for measuring a zone of separation in a substrate. This system (2) for measuring the propagation of a zone C of separation between a first portion (4) and a second portion (5) of at least one substrate (6) comprises: a module (10) for emitting at least two incident beams Fi each of which illuminates a separate point on the substrate (6), the at least two incident beams Fi being able to pass through the first portion (4) and the zone C of separation and meet the second portion (5) in such a way that each of them generates at least one first emergent beam Fe originating from the interface between the first portion (4) and the zone C of separation, and at least one second emergent beam Fe originating from the interface between the zone C of separation and the second portion (5); a detecting module (8) for detecting light intensity values resulting from interference between the first and second emergent beams Fe; and a computer (11) for determining the conditions of the propagation of the zone C of separation.