Abstract
The mid-infrared (mid-IR) anisotropic optical response of a material
probes vibrational fingerprints and absorption bands sensitive to order,
structure and direction dependent stimuli. Such anisotropic properties
play a fundamental role in catalysis, optoelectronic, photonic, polymer
and biomedical research and applications. Infrared dual-comb polarimetry
(IR-DCP) is introduced as a powerful new spectroscopic method for the
analysis of complex dielectric functions and anisotropic samples in the
mid-IR range. IR DCP enables novel hyperspectral and time-resolved
applications far beyond the technical possibilities of classical
Fourier-transform IR (FTIR) approaches. The method unravels
structure–spectra relations at high spectral bandwidth (100 cm–1) and
short integration times of 65 µs, with previously unattainable time
resolutions for spectral IR polarimetric measurements for potential
studies of noncyclic and irreversible processes. The polarimetric
capabilities of IR-DCP are demonstrated by investigating an anisotropic
inhomogeneous free-standing nanofiber scaffold for neural tissue
applications. Polarization sensitive multi-angle dual-comb transmission
amplitude and absolute phase measurements (separately for ss-, pp-, ps-
and sp-polarized light) allow the in-depth probing of the samples’
orientation dependent vibrational absorption properties. Mid-IR
anisotropies can be quickly identified by cross-polarized IR-DCP
polarimetry.