Method for characterizing a surface, and device therefor

An imaging device, comprising:

• a light source;
• a collimation system to generate a parallel light beam from a beam emitted by the light source;
• a polarizer to polarize the parallel light beam into polarized light;
• a rotating optical deflector system to reflect the polarized light into a collimated incident light beam;
• an optical prism having an apex angle, an entrance face, an exit face and a base provided with a sensitive film, the prism being characterized by its apex angle and by its refractive index;
• a first afocal optical conjugation system that:
• is located on a side of the entrance face of the prism;
• has a first optical axis that is fixed with respect to the prism and is oriented so that after the collimated incident light beam has passed through the first afocal optical conjugation system, the collimated incident light beam is directed toward the entrance face, is refracted, then strikes the base of the prism where it undergoes total reflection and emerges, after refraction, on the exit face, forming a reflected emergent beam;
• and
• has an orientation and an aperture that are such that the collimated incident light beam refracted on the entrance face illuminates all of at least what is called a useful part of the sensitive film, and undergoes thereon a total reflection when a direction of the collimated incident light beam exiting the first afocal optical conjugation system varies, on either side of the first optical axis, over an angular range of at least 10° in total, the useful part containing active zones whose optical thickness is likely to vary over time;
• a second afocal optical conjugation system that is placed on a side of the exit face of the prism, the second afocal optical conjugation system having a second optical axis, fixed with respect to the prism that is oriented so that, when the collimated incident light beam is parallel to the first optical axis, a second emergent beam parallel to the second optical axis exits the second afocal optical conjugation system;
• a detection system having a plane sensitive surface that is capable of receiving and analyzing the second emergent beam, the plane sensitive surface being perpendicular to the second optical axis;
• wherein:
• the second afocal optical conjugation system has an aperture such that any light emanating from the useful part passes through the aperture when the direction of the collimated incident light beam varies over the angular range;
• the second afocal optical conjugation system is configured such that any light emanating from the useful part illuminates the sensitive surface of the detection system;
• and
• the apex angle and the index of the prism are configured such that, when the direction of the collimated incident light beam is parallel to the optical axis of the first afocal optical conjugation system an intermediate image of the useful part that has passed through the exit face of the prism and that constitutes an object for the second afocal optical conjugation system, is perpendicular to the second optical axis.