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Figure: Theoretical spatial resolution (r) achievable for various NAs across the mid-IR wavenumber range for a refractive index through air (n = 1). The conversion to wavelength, in microns, is shown in green on the x-axis.
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For our “hybrid” macro-ATR technique using a Ge hemisphere (n = 4), the resolution is as follows:
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Figure: Theoretical spatial resolution (r) for the two objectives currently used with our “hybrid” macro-ATR technique. Calculation factors in the refractive index of the Ge hemisphere crystal and the doubling back of the light path through the objective.
NOTE: For the macro-ATR technique, the NA of the objective needs to be halved in the Rayleigh equation due to the light returning back through the same objective.