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}


    wavelength: {value: 1.54184, unit: angstrom}

without specifying the data type? Or is it better to create an own key like

    wavelength: {line: CuKa}