Hyperspectral mapping of anisotropy†
Anisotropy of absorbance (dichroism) and birefringence limits spatial resolution, sensitivity during quantitative detection of trace analytes, as well as spectral imaging in the near-IR and mid-IR spectral ranges. Here we show hyperspectral imaging capable of determining retardance and absorbance due to small changes in the real and imaginary parts of the refractive index ∼Δn and ∼Δκ at each single point of a measurement at diffraction limited resolution. This single-beam technique allows the retrieval of the phase and amplitude information by virtue of a twice different angular dependence of Δn and Δκ on the sample orientation angle. It has potential applications in analytical science, multi-dimensional optical memory devices, and forensic/defense/sensor fields.