41 research outputs found
Dynamic Response of a fast near infra-red Mueller matrix ellipsometer
The dynamic response of a near infrared Ferroelectric Liquid Crystal based
Mueller matrix ellipsometer (NIR FLC-MME) is presented. A time dependent
simulation model, using the measured time response of the individual FLCs, is
used to describe the measured temporal response. Furthermore, the impulse
response of the detector and the pre-amplifier is characterized and included in
the simulation model. The measured time-dependent intensity response of the MME
is reproduced in simulations, and it is concluded that the switching time of
the FLCs is the limiting factor for the Mueller matrix measurement time of the
FLC-based MME. Based on measurements and simulations our FLC based NIR-MME
system is estimated to operate at the maximum speed of approximately 16 ms per
Mueller matrix measurement. The FLC-MME may be operated several times faster,
since the switching time of the crystals depends on the individual crystal
being switched, and to what state it is switched. As a demonstration, the
measured temporal response of the Mueller matrix and the retardance of a thick
liquid crystal variable retarder upon changing state is demonstrated.Comment: to be published in Journal of Modern Optics 20 pages, 6 figure
Mueller matrix measurements and modeling pertaining to Spectralon white reflectance standards
The full Mueller matrix for a Spectralon white reflectance standard was measured in the incidence plane, to obtain the polarization state of the scattered light for different angles of illumination. The experimental setup was a Mueller matrix ellipsometer, by which measurements were performed for scattering angles measured relative to the normal of the Spectralon surface from −90° to 90° sampled at every 2.5° for an illumination wavelength of 532 nm. Previously, the polarization of light scattered from Spectralon white reflectance standards was measured only for four of the elements of the Muller matrix. As in previous investigations, the reflection properties of the Spectralon white reflectance standard was found to be close to those of a Lambertian surface for small scattering and illumination angles. At large scattering and illumination angles, all elements of the Mueller matrix were found to deviate from those of a Lambertian surface. A simple empirical model with only two parameters, was developed, and used to simulate the measured results with fairly good accuracy.publishedVersio
Effects of optical activity to Mueller matrix ellipsometry of composed waveplates
Mueller matrix ellipsometry has been used to precisely characterize quartz waveplates for demanding applications in the semiconductor industry and high precision polarimetry. We have found this experimental technique to be beneficial to use because it enables us to obtain absolute and precise measurement of retardation in a wide spectral range, waveplate orientation, and compound waveplate adjustment. In this paper, the necessity of including the optical activity in the Mueller matrix model and data treatment is demonstrated. Particularly, the optical activity of the quartz influences the adjustment of misalignment between the perpendicularly oriented waveplates of the compound biplate. We demonstrate that omitting the optical activity from the model leads to inaccurate values of the misalignment. In addition, the depolarization effects caused by a finite monochromator bandwidth is included in the model. Incorporation of the optical activity to the Mueller matrix model has required a development of rigorous theory based on appropriate constitutive equations. The generalized Yeh's matrix algebra to bianisotropic media has been used for the calculation of the eigenmodes propagation in chiral materials with reduced symmetry. Based on the applied method, the authors have proposed approximated analytical form of the Mueller matrix representing optically active waveplate and biplate and provided discussion on the analytical and numerical limits of the method.Web of Science297104501043
True Circular Dichroism in Optically Active Achiral Metasurfaces and Its Relation to Chiral Near-Fields
Optically active achiral metasurfaces offer a promising way to detect chiral
molecules based on chiroptic methods. The combination of plasmonic enhanced
circular dichroism and reversible optical activity would boost the sensitivity
and provide enantiomerselective surfaces while using a single sensing site. In
this work, we use metasurfaces containing arrays of U-shaped resonators as a
benchmark for analyzing the optical activity of achiral materials. Although the
peculiar optical activity of these metasurfaces has 1 been quite well
described, we present here an experimental and numerical quantitative
determination of the different contributions to the measured optical activity.
In particular, it is shown that linear birefringence and retardance contribute,
but only marginally, to the apparent circular dichroism of the metasurface
associated with the excitation of magnetoelectric modes. We then numerically
demonstrate the peculiar near-field properties of the magneto-electric modes
and explain how these properties could be reflected in the far-field
polarimetric properties in the presence of chiral molecules. This work provides
alternatives for the detection scheme of chiral molecules using plasmonic
resonators.Comment: ACS Applied Optical Materials, 202
Fast and optimal broad-band Stokes/Mueller polarimeter design by the use of a genetic algorithm
A fast multichannel Stokes/Mueller polarimeter with no mechanically moving
parts has been designed to have close to optimal performance from 430-2000 nm
by applying a genetic algorithm. Stokes (Mueller) polarimeters are
characterized by their ability to analyze the full Stokes (Mueller) vector
(matrix) of the incident light. This ability is characterized by the condition
number, , which directly influences the measurement noise in
polarimetric measurements. Due to the spectral dependence of the retardance in
birefringent materials, it is not trivial to design a polarimeter using
dispersive components. We present here both a method to do this optimization
using a genetic algorithm, as well as simulation results. Our results include
fast, broad-band polarimeter designs for spectrographic use, based on 2 and 3
Ferroelectric Liquid Crystals, whose material properties are taken from
measured values. The results promise to reduce the measurement noise
significantly over previous designs, up to a factor of 4.5 for a Mueller
polarimeter, in addition to extending the spectral range.Comment: 10 pages, 6 figures, submitted to Optics Expres
New spark test device for material characterization
An automated spark test system based on combining field emission and spark measurements, exploiting a discharging capacitor is investigated. In particular, the remaining charge on the capacitor is analytically solved assuming the field emitted current to follow the Fowler Nordheim expression. The latter allows for field emission measurements from pA to A currents, and spark detection by complete discharge of the capacitor. The measurement theory and experiments on Cu and W are discussed