Mid‐infrared dual‐comb polarimetry of anisotropic samples

Abstract

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 approaches. The method unravels structure–spectra relations at high spectral bandwidth up to 90 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 freestanding 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 quickly be identified by cross‐polarized IR‐DCP polarimetry. Key points A novel dual‐comb laser‐based technique is established for polarization‐dependent mid‐infrared spectroscopy. Independent measurements of spectral s‐ and p‐polarized transmission amplitudes and phases in the μs range. Visualization of the anisotropy of nanofiber scaffolds as used for neural tissue applications.

Keywords

• anisotropy
• dual‐comb spectroscopy
• infrared laser
• mid‐infrared spectroscopy
• nanofiber
• polarimetry