Synchrotron infrared confocal microscope: Application to infrared 3D spectral imaging

The brightness of a synchrotron source coupled to an infrared microscope allows imaging at the so-called diffraction limit. Thus, numerous infrared beamlines around the world have been developed for infrared chemical imaging. Infrared microscopes employ Schwarzschild objectives, which are based on two spherical mirrors centered on a common optical axis. A common drawback of the latter design comes with the central obscuring of the incident beam and the corresponding diffraction effects. However, in this work we are taking advantage of the "shadow" below the primary mirror in order to "vertically" probe our sample and record depth profiling images. We recorded infrared confocal images of liquid water occluded inside a quartz micro-cavity and reconstructed a 3D infrared image based on the OH stretching vibrational bands. Although only a restricted sample size can be analyzed, we demonstrate here the feasibility of a 3D confocal infrared measurement. The chemical profiles have been calculated along the Z-axis of the water inclusion to study its heterogeneity and water-solid interfaces.