The VLT Interferometer - ESO

in Table I for incidence angles 9 equal to 45 and 60 degrees (a quarter
wave retardation corresponds to 90 0 retardation). Also shown in Table I
are the measurements for a silver over chrome coating of interest for
astronomical interferometry3.
Both polarization and retardation vary approximately as 9 3 for small
incidence angles. At visible wavelengths the polarization /retardation
effects are substantial especially when one considers the presence of
a number of these reflections in the beam. At infrared wavelengths the
effects are minor. Since the magnitude of the effects sharply increase
wi th e it is important to keep the incidence angles as small as
possible. More complex multilayer coatings in which the reflectivity is
optimized will reduce the amount of polarization but the retardance will
stay in general high.
3. FORMALISM FOR ANALYZING FRINGE CONTRAST AND PHASE EFFECTS
Sections 3.1 and 3.2 will summarize the part of the Jones calculus
of interest for the current application. Section 3.3 will then derive
the formalisms specific to astronomical interferometry.
3.1 The Jones vector : J
In Jones Calculus the state of polarized light is expressed by a
vector J which has the form:
J =
Aqexp (iEq)
where (p,q) are a set of predefined linear orthogonal coordinates, where
Ap and Aq are the amplitudes of the electromagnetic waves, and where Ep
and Eq are their phases (in radians) .
TABLE II
Jones Vectors for Assumed Incident Polarization States
State Type: Ap Aq Ep Eq
I Linear (0.=0) 1 0 0 0
II Linear (0.=90) 0 1 0 0
III Linear (0.=45) 1.5 1.5 0 0
IV Linear (0.=-45) 1.5 -1.5 0 0
V Right Circular 1.5 1.5 -rr/2 0
VI Left Circular 1.5 1.5 rr/2 0
(1)