Here are the description of ior file as found with the SOPRA database:
A full ior file (or complex ior file) stores the index of refraction (N) and absorption or extinction coefficient (K) for each wavelenght. It is an ASCII file that follows this specification :
The first number indicates the spectral unit (1 = eV, 2 = µm, 3 = cm-1, 4 = nm )
<spectral_unit> <spectral_range> <spectral_range> <number_of_intervals>
1 1.5 6 90
this file provide the n and k values for water at energies ranging from 1.5 to 6 eV for 90 intervals (hence it contains 91 n and k values). The measured k values being very low are rounded down to 0.
Note that the unit part (first number) has been omitted in the Maxwell manual, though some ior use another unit than eV (1) and seem to work ok nevertheless.
Any n/k dataset reasonably complete in the visible spectrum can be used to make an ior file. It may need some interpolation to have even intervals. I found that Findgraph software ( http://www.findgraph.com/
) is convenient to get an interpolated dataset. I haven't tryied it yet, but it seems that you can even retrieve a dataset from a scanned curve.
The journey's FAR from over
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