Special enhanced silver mirror coatings were designed and fabricated to minimize the polarization introduced by a three-mirror
off-axis high-accuracy telescope. A system diattenuation of approximately 1% in the VIS-NIR was achieved by
both reducing the diattenuation from each mirror individually and by balancing the diattenuations introduced by the
three mirrors over the spectral range. This process of low-polarization engineering involves minimizing system
polarization introduced by surface geometry, thin film coatings and birefringent elements, and measuring the system. In
this report we will outline a methodology to minimize instrumental polarization aberrations, with an emphasis on
achieving low diattenuation in the MSPI camera, given its off-axis geometry and coating design constraints imposed by
the space-based application. This polarization balancing technique for mirror coatings can be applied to astrophysics
applications.
Biaxial ellipsometry is a technique that measures the dielectric tensor and thickness of a biaxial substrate, single-layer
thin film, or multi-layer structure. The dielectric tensor of a biaxial material consists of the real and imaginary parts of
the three orthogonal principal indices (nx+ ikx, ny+ iky and nz + ikz) and three Euler angles (Θ, Φ, Δ) to describe its
orientation. The method utilized in this work measures an angle-of-incidence Mueller matrix from a Mueller matrix
imaging polarimeter equipped with a pair of microscope objectives with low polarization aberrations. The dielectric
tensors for multilayer samples are determined from multi-spectral angle-of-incidence Mueller matrix images in either a
transmission or reflection mode using an appropriate dispersion model. Given approximate a priori knowledge of the
dielectric tensor and film thickness, a Jones matrix image is first calculated by solving Maxwell's equations at each
surface which is then transformed into a Mueller matrix image. An optimization algorithm then finds the best fit
dielectric tensor based on matching the measured and calculated angle-of-incidence Mueller matrix images. One use for
this application is to more accurately determine the dielectric tensors of biaxial films used in liquid crystal displays.
Polarization-sensitive optical systems include those requiring very accurate irradiance measurements and those where
polarization is the intended measurement. Low-polarization optical system design is the process of minimizing system
polarization introduced by surface geometry, thin film coatings and birefringent elements, and measuring system
components to verify polarization performance. The complicated, multi-step, iterative low polarization optical system
design process requires initial system design, witness sample fabrication and measurement, reverse engineering of
fabricated coatings and coating redesign, end-to-end system polarization aberration analysis, and system measurement
and calibration. Most of this process will be spent iterating between design and measurement phases until a final design
is reached that can be fabricated and calibrated to perform within the desired system tolerances. This work discusses
low polarization optical system design using a three-mirror off-axis camera as an example.
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