System for generating a signal representative of the profile of a surface moving relative to the system

A system (1) for generating at least one signal representative of the profile of an outer surface (22) of a medium (21) having a median plane (23) and having a relative speed V with respect to the system in a direction U, comprising:

• a first light source (2) able to emit a first light beam, the first light beam being a Gaussian beam of coherent and monochromatic light, a wavelength λ1 of which is adapted to optical absorption characteristics of the medium (21), along a first optical path (11);
• a first sensor (3) able to evaluate effects of electromagnetic interference between a portion of the first light beam and a portion of the first light beam backscattered from the outer surface (22) of the medium (21) of the first light beam, and delivering a first electrical signal;
• a means (2′, 4) for generating at least one second light beam, the at least one second light beam being a Gaussian beam of coherent and monochromatic light of wavelength λ2 adapted to the optical absorption characteristics of the medium (21) along a second optical path (12);
• a second sensor (3′) located on the second optical path (12) able to evaluate effects of electromagnetic interference between a portion of the second light beam and a portion of the second light beam backscattered from the outer surface (22) of the medium (21), and delivering a second electrical signal;
• at least one first focusing lens (5, 6) located on the first and/or the second optical path (11, 12) for focusing all or part of a corresponding light beam at a focusing distance f and defining an upstream optical path (11′, 12′);
• and
• a means (4′, 7) for routing the at least one second light beam able to redirect at least a portion of the second optical path (12′) in the same direction as a portion of the first optical path (11′),
• wherein the two optical paths (11′, 12′) are coplanar,
• wherein the wavelengths of the first and second light beams have the same sensitivity to the optical reflectivity characteristics of the outer surface (22) of the medium (21),
• wherein a combination of the focusing distance (f1, f2) and the optical path (11′, 12′) for each light beam defines two distinct geometric points d1 and d2 corresponding to a focal point of each light beam,
• wherein a distance between the geometric points d1 and d2 is greater than a greatest Rayleigh length of the first and second light beams, and
• wherein direction vectors of the first and second optical paths (11′, 12′) define an angle θ less than 3 degrees.