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.

Terahertz Vortex Beam as a Spectroscopic Probe of Magnetic Excitations

“…The experimental temperature dependencies of the LF and KK excitations in Dy-IG ( Fig. 3) are similar to that for antiferromagnetic resonances, or magnons at ⃗ k ¼ 0, in the magnetically ordered system with several interacting spins [39][40][41]. Interaction of the LF and KK modes in Dy-IG with vortex optical beams is the main focus of our experiments.…”

Spectral signatures of spin–phonon and electron–phonon interactions in multiferroic iron borates

“…Samples with dimensions up to 5x5x10 mm were oriented using the crystal morphology and optical (2 -300 K). FIR ellipsometry measurements were also performed, using self-made ellipsometer on the U4IR beamline of the National Synchrotron Light Source, Brookhaven National Laboratory, USA [26]. Raman measurements were performed in a backscattering configuration, as described in Ref.…”

Fano Resonances in the Infrared Spectra of Phonons in HyperkagomeNa3Ir3O8

“…Experimental details can be found in Refs. [30,31]. The complex dielectric functionεðωÞ ¼ ε 1 ðωÞ þ iε 2 ðωÞ and the related optical conductivity σ 1 ðωÞ ¼ ωε 2 ðωÞ=ð4πÞ were determined by direct inversion of the Fresnel equations from the ellipsometric parameters ΨðωÞ and ΔðωÞ.…”