Fig. 4: Scaling of the diffusion coefficient.

a D(W, L) for \(W=(N+\frac{1}{2}){\lambda }_{0}/2\) is plotted for different values of W/(λ₀/2). The diffusion coefficient may be defined according to Fick’s first law as long as the derivative of energy density within the sample is nearly constant, which is the case down to values of g close to unity. The diffusion coefficient, as given by Eq. (3) and (4), is plotted as dashed curves once g < 1 since u(z) then no longer falls linearly. b The variation of the diffusion coefficient with wavelength for each N is plotted for sample lengths at which the diffusion coefficient in (a) is at its maximum.