\begin{equation} \frac{\partial |\widetilde{H}|^{2}}{\partial \omega} = \frac{-1/k^{2}2\left(\displaystyle -2\frac{\omega}{\omega_{0}^2}\right)\left(\displaystyle 1-\left(\frac{\omega}{\omega_{0}}\right)^{2}\right)} {\left[\displaystyle \left(1-\left(\frac{\omega}{\omega_{0}}\right)^{2}\right)^{2}+\eta^{2}\right]^2} \end{equation}