Patent Document ID: 4571082
Application ID: 06495431
Patent Status: 1

Claim One:
1. An interference refractometer comprising beam splitting means arranged to divide an incident beam of electromagnetic radiation into first and second spaced parallel partial beams having components of substantially equal intensity in two orthogonal directions of radiation, reflection means spaced from the beam splitting means and arranged to reflect said first partial beam along its path to said reflection means and said second partial beam along a parallel path, a test device positioned between the beam splitting means and the reflection means so that said first partial beam will traverse a path of known length therein, phase shifting means arranged to introduce a phase shift of substantially 90 degrees between radiation polarised in two orthogonal directions in one of the two partial beams, a polarising beam splitter arranged to receive from the beam splitting means radiation having components of substantially equal intensity derived from the first and second partial beams, first and second radiation sensing means each arranged to receive from the polarising beam splitter radiation polarised at one of said two orthogonal directions, third radiating sensing means arranged to receive from the beam splitting means radiation derived only from the second partial beam and signal subtraction means for extracting a signal derived from the third sensing means from each of the first and second sensing means.