Broadband sum frequency generation via chirped quasi-phase-matching
  An efficient broadband sum frequency generation (SFG) technique using the two collinear optical parametric processes \omega 3=\omega 1+\omega 2 and \omega 4=\omega 1+\omega 3 is proposed. The technique uses chirped quasi-phase-matched gratings, which, in the undepleted pump approximation, make SFG analogous to adiabatic population transfer in three-state systems with crossing energies in quantum physics. If the local modulation period %for aperiodically poled quasi-phase-matching first makes the phase match occur for \omega 3 and then for \omega 4 SFG processes then the energy is converted adiabatically to the \omega 4 field. Efficient SFG of the \omega 4 field is also possible by the opposite direction of the local modulation sweep; then transient SFG of the \omega 3 field is strongly reduced. Most of these features remain valid in the nonlinear regime of depleted pump. 
A. A. Rangelov and N. V. Vitanov
physics.optics quant-ph