Accurate measurement of the optical constants (n,k) requires an absorptive (i.e. transmission) and dispersive (i.e. reflectance) measurement. Ellipsometry is the gold standard for such measurements, particularly on opaque samples where typical techniques fail to provide an absorptive spectrum. However, an alternative to ellipsometry is needed for microscopy because of the inherent range of angles and planes of incidence when focusing to a small spot.
Here we present early images from our complex far-field spectroscopic infrared microscope. An asymmetric interferometer is used to directly measure the infrared reflectance amplitude and absolute phase shift. The complex optical constants can then be extracted without the large uncertainty that arises with a reflectance amplitude measurement alone. Modern QCL sources provide sufficient infrared intensity to realize a type-2 scanning microscope, to achieve a resolution of λ/4 N.A., twice the traditional Abbe limit.
|