N & K Extraction from Spectra

If the n & k values of the layer materials used in a process to produce an optical thin film coating are not adequately known, the resulting products will not agree with the designs. This problem can be overcome by depositing a single layer of each of the materials of interest on an appropriately prepared substrate, measuring the spectral results in %T versus wavelength (or wavenumber), and using these spectra to find the n & k values which fit the spectral results. These n & k values can then be used in the designs to better represent what is expected from the deposition process. The process of extracting the n & k values from the spectra is not always easy for every coating operation to perform for themselves, or they may want a second opinion on the n & k values. We offer this service for a reasonable fee per n & k value extraction.

Data Needed for Reasonable Index Extraction

Spectrophotometer Make and Model

100% transmittance (%T) spectrum over the intended range of spectral measurements with no sample in the beam.

0% transmittance spectrum over the range of spectral measurements with an opaque sample in the beam.

%T spectrum over the range of spectral measurements with uncoated substrate in the beam.

%T spectrum over the range of spectral measurements with coated substrate in the beam.

Measured or estimated coating thickness, and how measured or estimated.


Dielectric layers must be thick enough to provide at least 3 extrema (max or min) in the spectral range measured.

Metallic and Cermet layers must also include reflectance (%R) spectra at near normal incidence (<10°) of:

1) the uncoated substrate,
2) no sample (0%R),
3) the %R from the coated side,
and 4) the %R from the uncoated side.
(Such metallic films may not exhibit the extrema of dielectric layers.)

Fee Per Extraction:

One Extraction of n and k represents one layer from the spectra supplied as listed above.

The Introductory Offer to the first ten (10) extractions purchased is: $150 per for a Dielectric layer and $250 per for a Metallic or Cermet layer.

Prepayment in advance is required by Credit Card, Check, or Wire Transfer.


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