title: Exact eigenstates for a class of models describing two-mode multiphoton processes.
abstract: We present an efficient approach to studying the spectra and eigenstates for nonlinear models describing multiphoton processes. We obtain the exact explicit analytical expressions of all the energy spectra and eigenstates in terms of a parameter for a class of models describing two-mode multiphoton processes. The parameter is shown to be determined by the roots of a simple polynomial.