Infrared spectroscopy: New frontiers both near and far

Until very recently, the conventional optical resolution limits for far-field infrared (IR) imaging were ~5-10 µm, given the 2-25 µm wavelengths and the typical optics of mid-IR microscopes. In 2011, the diffraction limit for far-field IR was achieved with synchrotron source light, high numerical aperture (NA) optics, and a focal plane array detector. Comparable capability for thermal-source IR microscopes is now commercially available. Single-wavelength scanning, with quantum cascade lasers, and fast, full spectrum imaging, with focal plane array detectors, permit collection of infrared images on samples with dimensions on the order of centimeters, within minutes. Near-field IR techniques embody a conceptual paradigm shift, preserving the analytical power of IR spectroscopy, while breaking the diffraction limit constraints for a 100-fold improvement in spatial resolution. Exploration of the chemistry of materials at micrometer and nanometer scales leads to a better macroscopic perspective, as illustrated here with examples from our ongoing research in materials, environmental, and biomedical applications.