title: Synchrotron radiation-based far-infrared spectroscopic ellipsometer with full Mueller-matrix capability.
abstract: We developed far-IR spectroscopic ellipsometer at the U4IR beamline of the National Synchrotron Light Source in Brookhaven National Laboratory. This ellipsometer is able to measure both, rotating analyzer and full-Mueller matrix spectra using rotating retarders, and wire-grid linear polarizers. We utilize exceptional brightness of synchrotron radiation in the broad spectral range between about 20 and 4000 cm(-1). Fourier-transform infrared (FT-IR) spectrometer is used for multi-wavelength data acquisition. The sample stage has temperature variation between 4.2 and 450 K, wide range of θ-2θ angular rotation, χ tilt angle adjustment, and X-Y-Z translation. A LabVIEW-based software controls the motors, sample temperature, and FT-IR spectrometer and also allows to run fully automated experiments with pre-programmed measurement schedules. Data analysis is based on Berreman's 4 × 4 propagation matrix formalism to calculate the Mueller matrix parameters of anisotropic samples with magnetic permeability μ ≠ 1. A nonlinear regression of the rotating analyzer ellipsometry and∕or Mueller matrix (MM) spectra, which are usually acquired at variable angles of incidence and sample crystallographic orientations, allows extraction of dielectric constant and magnetic permeability tensors for bulk and thin-film samples. Applications of this ellipsometer setup for multiferroic and ferrimagnetic materials with μ ≠ 1 are illustrated with experimental results and simulations for TbMnO3 and Dy3Fe5O12 single crystals. We demonstrate how magnetic and electric dipoles, such as magnons and phonons, can be distinguished from a single MM measurement without adducing any modeling arguments. The parameters of magnetoelectric components of electromagnon excitations are determined using MM spectra of TbMnO3.
authors: Department of Physics, New Jersey Institute of Technology, Newark, New Jersey 07102, USA. stantar@njit.edu
authors: T N
authors: TN
authors: Stanislavchuk
authors: T D
authors: TD
authors: Kang
authors: P D
authors: PD
authors: Rogers
authors: E C
authors: EC
authors: Standard
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authors: Basistyy
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authors: AM
authors: Kotelyanskii
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authors: G
authors: Nita
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authors: Zhou
authors: G L
authors: GL
authors: Carr
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authors: M
authors: Kotelyanskii
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authors: Sirenko