When using an x-ray reflectometer, it is more exact to mention the cathode and line
rather than the wavelength. Eg. CuKa or CuKa1. For this also includes the resolution.
Is it possible to use
wavelength: {value: CuKa}
or
wavelength: {value: 1.54184, unit: angstrom}
without specifying the data type? Or is it better to create an own key like
wavelength: {line: CuKa}