m is an exponent which expresses the shape of a peak function (m = 2 for a Lorentzian); and 1/ξpeak is a peak width at half-maximum manifesting the spatial extent of a scatterer size ξpeak. In principle, the ξpeak and ξOZ parameters, are independent from each other, however in all our fittings they would yield nearidentical values, thus in the final refinement we decided to use a single-variable parameterization in which ξpeak= ξOZ.