  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.
