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.