Comment on "Normalization of quasinormal modes in leaky optical cavities and plasmonic resonators"

Recently, Kristensen, Ge, and Hughes [Phys. Rev. A92, 053810 (2015)] have compared three different methods for normalization of quasinormal modes in open optical systems and concluded that they all provide the same result. We show here that this conclusion is incorrect and illustrate that the normalization of P. T. Kristensen et al., Opt. Lett. 37, 1649 (2012), is divergent for any optical mode having a finite quality factor, and that the Silver-Muller radiation condition is not fulfilled for quasinormal modes.