“…One could obtain the Lagrangian and define appropriate creation and annihilation operators applying the method introduced in Ref. 41 , which satisfy the harmonic oscillator commutation relations. The Hamiltonian is: where , , , , and R(t) are mode operators, electric displacement operator, vacuum permittivity, medium permittivity, and response function of the medium (which is absent in Drummond’s works 8 , 9 , 59 , 60 and our earlier works 36 , 40 , 41 ), respectively.…”