## A.1 The IMD optical constant database

The IMD optical constant database is located in the directory called `nk.dir`, in the `imd` directory. Optical constant files are designated by a '`.nk`' extension, and are ASCII files containing three columns of numbers: wavelength (in angstroms), n, and k. Comment lines (beginning with a semicolon) may precede the data.

Each 'nk' file in `nk.dir` corresponds to one material, although there is usually more than one nk file for any given material. The naming convention I have adopted for nk files is `Material_reference.nk`. For example, the file `Si_palik.nk` corresponds to the optical constants for silicon, taken from the optical constant handbook by Palik [18]; the file `Si_llnl_cxro.nk` corresponds to other data for silicon, in this case data in the X-ray region compiled from the LLNL and CXRO atomic scattering factors (see section A.3 below.) Source reference information is usually included as a comment at the beginning of the file. In addition to these source-specific files, for every material I have created compilation files that cover as wide a range in wavelength as possible. The compilation files include no reference in the name. For example, the file `Si.nk` is a compilation of the data from `Si_llnl_cxro.nk` and `Si_palik.nk`, and spans the range from 0.124 angstroms to 3.33e6 angstroms.

To use a specific file for a given material, enter the full name of the file (excluding the `.nk` extension) in the Material fields in the relevant `ambient`, `layer`, or `substrate` widgets (be sure that the Optical constants file name button is checked, rather than the `Composition and density` button.). For example, to use the data for silver published by Hagemann, et al, specify `Ag_hagemann`, instead of just plain `Ag`.

The nk files contained in the `nk.dir` directory are listed in the file called `AAACATALOG.TXT`, which is also located in `nk.dir`. This file is displayed when you select `Materials/Optical Constants -> Browse Optical Constants Database` from the IMD menu bar.

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