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[Probeman]

The origin of multi-layer x-ray diffractors is discussed in this recent Veritasium video:

https://www.youtube.com/watch?v=MiUHjLxm3V

I was lucky enough to work with Jim Underwood (mentioned in the video) after he moved to LBL and I was starting on the ARL microprobe trying to improve detection of N Ka for Tony Tomsia using custom NiCr/BN multilayers back in the 1990s which he manufactured for me.

On a JEOL instrument N Ka corresponds to a spectrometer position of ~138mm  with this diffractor:

n  ka on NiCrBN (2d=65 A) (Spc=140 mm), is 138.3364 (with refractive index correction, k= 0.016)

Note that the latest CalcZAF now includes the 2d spacing for this calculation output, which is nice for multi-layer diffractors since they can be manufactured in a range of different 2ds.