Low-bulk interferometric sensor
The present invention relates to an objective ( 3 ) for a confocal system ( 1 ) of spectral interferometric measurement, comprising: —a source hole ( 14 ); —a second beam splitter ( 12 ) having a partially reflective face ( 12 a ), —a first beam splitter ( 10 ) having a face which is configured to form a reference surface ( 6 ) and being located between the source hole ( 14 ) and the second beam splitter ( 12 ); and—lenses ( 11, 13 ). The first and second beam splitters are positioned in the objective ( 3 ) such that an optical distance (d ref ) between the reference surface ( 6 ) and the partially reflective surface ( 12 a ) is substantially equal to an optical distance (d m ) between the partially reflective surface ( 12 a ) and a focal plane of the objective ( 3 ).
1 . An objective for a confocal system for spectral interferometric measurement comprising:
a source hole;
a first beam splitter having a face configured to form a reference surface, wherein the first beam splitter comprises at least one of the following elements: an assembly formed of a lens and a partially reflective plate, a lens having a face devoid of anti-reflective treatment, and an assembly comprising a mirror attached and fixed to a lens, an area of the mirror being less than an area of the lens;
a second beam splitter having a partially reflective face, the second beam splitter being positioned downstream of the first beam splitter such that the first beam splitter is located between the source hole and the second beam splitter and that an optical distance between the reference surface and the partially reflective surface is substantially equal to an optical distance between the partially reflective surface and a focal plane of the objective; and
a first lens positioned between the first beam splitter and the second beam splitter and a second lens positioned downstream of the second beam splitter, an optical distance between the first lens and the second beam splitter being equal to an optical distance between the second beam splitter and the second lens;
wherein the first beam splitter, the second beam splitter, the first lens and the second lens are coaxial such that optical axes of the first beam splitter, of the second beam splitter, the first lens and the second lens are coincident.
2 . The objective according to claim 1 , wherein optical characteristics of the first lens and of the second lens are identical.
3 . The objective according to claim 2 , wherein the distance between the first lens and the second beam splitter is equal to the distance between the second beam splitter and the second lens.
4 . The objective according to claim 1 , further comprising a mirror mounted downstream of the first beam splitter, the second beam splitter and the first and second lenses, the mirror being inclined with respect to the optical axis of the first and second lenses in order to bend a light beam that it receives from the first and second lenses.
5 . The objective according to claim 1 , wherein the first beam splitter is divergent and the first lens is convergent.
6 . The objective according to claim 1 , wherein the source hole also forms a filtering hole of the objective.
7 . A confocal system for spectral interferometric measurement comprising a light source and an objective according to claim 1 , wherein the light source is connected to the source hole.
8 . The system according to claim 7 , wherein the light source is polychromatic.
9 . The system according to claim 7 further comprising a processing unit connected to the objective, the processing unit being configured to characterise a surface of a sample based on recombined light beams reflected on the surface of the sample and on the reference surface.
10 . The system according to claim 9 , wherein the processing unit comprises a spectrograph connected to the objective via an optical fibre.
11 . The objective according to claim 1 , wherein the focal distance of the first lens and of the second lens are identical.
12 . The objective according to claim 1 , wherein the first beam splitter is convergent and the first lens is divergent.
13 . The confocal system according to claim 7 , wherein the light source is connected to the source hole by an optical fibre.