Patent ID: 7554678

Claim:
A device for measuring the thickness of a transparent sample ( 2 ), said device comprising: a first incident light beam (L 1 ) obliquely incident on a front surface( 8 ) of the transparent sample ( 2 ) at a first incident angle (α 1 ); a second light beam (L 2 ) obliquely incident on said front surface ( 8 ) of the transparent sample ( 2 ) at a second incident angle (α 2 ), the first incident angle (α 1 ) and the second incident angle (α 2 ) differing from each other; a third incident light beam (L 3 ) parallel to the first incident light beam (L 1 ) or paralle to the second incident light beam (L 2 ), said third incident light beam (L 3 ) being directed toward said front surface ( 8 ) of the transparent sample ( 2 ); a first detector ( 11 ) that detects respective reflected light beams (L 1 ′,L 1 ″) produced by partial reflection of the first incident light beam (L 1 ) from said front surface ( 8 ) and from a rear surface ( 13 ) of the transparent sample ( 2 ), that determines corresponding positions of both of said reflected light beams (L 1 ′, L 1 ″), and that determines a spacing between said reflected light beams (L 1 ′, L 1 ″) produced by partial reflection of the first incident light beam (L 1 ) from said front surface and from said rear surface; and a second detector ( 12 ) that detects respective reflected light beams (L 2 ′, L 2 ″) produced by partial reflection of the second incident light beam (L 2 ) from said front surface ( 8 ) and from said rear surface ( 13 ) of the transparent sample ( 2 ), that determines corresponding positions of both of said reflected light beams (L 2 ′, L 2 ″) and a spacing between said reflected light beams (L 2 ′,L 2 ″) produced by partial reflection of the second incident light beam (L 2 ) from said front surface and from said rear surface; wherein one of said first detector ( 11 ) and said second detector ( 12 ) is arranged to detect a reflected light beam (L 3 ′) produced by partial reflection of the third incident light beam (L 3 ) from the transparent sample ( 2 ) and to determine a position of the reflected light beam (L 3 ′) produced by partial reflection of the third incident light beam (L 3 ) from the transparent sample ( 2 ).