Anisotropy Studied by Polarization-Modulated Fourier Transform Infrared Reflection Difference Microspectroscopy

Abstract

We investigated anisotropic optical behavior in solid-state materials using Fourier transform infrared reflection microspectroscopy in combination with polarization modulation. For a Ca1.8Sr0.2RuO4 crystal with an isotropic optical surface, we found the reflection difference to be very close to zero, independent of the azimuthal angle of the sample. A Ca1.4Sr0.6RuO4 crystal with an anisotropic optical surface, however, exhibited a large anisotropic optical response with a strong angular dependence following a sinusoidal behavior. Furthermore, we examined the spatial distribution of the reflection difference in Bi0.17Ca0.83MnO3+delta using infrared synchrotron radiation and could clearly distinguish microscopic anisotropic domains having different optical axes. These results demonstrate that our experimental scheme can be used as a powerful tool to spectrally and spatially resolve anisotropy of solid-state materials in the mid-infrared region.

Polarization-modulated infrared reflection difference microspectroscopy: Experiment and model

“…The PM instrumental setup and its implementation in infrared reflection difference microspectroscopy are described in detail elsewhere [26,29,30]. In brief, the setup contains a polarizer (Specac, holographic aluminium grid, KRS-5) and a photoelastic modulator (Hinds Instruments, PEM-90 II, ZnSe, 50 kHz) between the spectrometer and the microscope.…”

“…1 The spectra were recorded in about 30 s at a spectral resolution of 4 cm À1 with a 40 Â 40 lm 2 aperture, with the k/2 peak retardation of the photoelastic modulator set for 2000 cm À1 . The spatial resolution in the measurements was found to be adequate to map or distinguish micrometric anisotropic domains with different crystallographic axes in multi-domain crystalline samples [26,27]. The obtained spectra have peculiar spectral shapes, resembling sinusoidal oscillations that decay towards higher wavenumbers and that have multiple arches and nodes.…”

“…3b), which was used to investigate anisotropic properties in more detail. Studying the azimuthal angular dependence of the reflection difference it was possible to distinguish micrometric anisotropic domains with different crystallographic axes in multi-domain crystalline samples and to observe a rotation of the optical axis in Bi 0.3 Ca 0.7 MnO 3+d across a phase transition [26,27]. The values shown in Fig.…”

“…Theoretical treatments [3,13] as well as experimental calibration procedures [10,13,20,23] taking account of these artifacts in PM experiments have been reported. With respect to polarization-modulated infrared reflection difference microspectroscopy, the issue of experimental artifacts was touched on previously [26,27]. In this article, an extended account is given, presenting experimental data along with model calculations and discussing the implications of our results.…”

“…Recently, we implemented an experimental scheme using Fourier transform infrared reflection microspectroscopy in combination with polarization modulation and demonstrated its potential to spectrally and spatially resolve anisotropy of solid-state materials in the mid-infrared region [26]. This technique enabled the local probing of charge and orbital ordering-induced anisotropy of a Bi 0.3 Ca 0.7 MnO 3+d crystal [27].…”