There are two important points in this paper. The first is a measure of surface scatter. Typically this would be specified as a scatterance or total integrated scatter (TIS). Instead, the measure here is based on an angle limited measurement with a nonstandard calibration. The surface scatter phase function and the solid angle of the temperature sensor must be known in order to get the TIS. For Rayleigh scatter, which the λ-4 dependence of the intercept indicates (surface absorption should be linear in frequency), the phase function is known. If the solid angle can be determined and calibration established, then a more useful scatter metric can be derived. The Rayleigh scattering interpretation of the zero-path intercept point is supported by a λ-4 dependence in these experiments and we look forward to further investigations. This is an interesting development that could be very useful for low loss material characterization.
The second point is that the measured absorption coefficient fits a weak absorption tail model and is one order of magnitude below values reported in the Handbook of Optical Constants for diamond. This is an important statement on the progress that has been made on optical quality synthetic diamond. Measurements like this need to be made on a wide range of window materials and we look forward to future publications from this group.
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