Steady-State Ab Initio Laser Theory for N-level Lasers
  We show that Steady-state Ab initio Laser Theory (SALT) can be applied to find the stationary multimode lasing properties of an N-level laser. This is achieved by mapping the N-level rate equations to an effective two-level model of the type solved by the SALT algorithm. This mapping yields excellent agreement with more computationally demanding N-level time domain solutions for the steady state. 
Alexander Cerjan, Yidong Chong, Li Ge, A. Douglas Stone
physics.optics