A model of three-wave parametric interactions is presented, in both type I and type II noncollinear phase-matching conditions, in which the group velocities of the interacting pulses are suitably linked to each other. We consider hva conditions for group velocities that are significant in the parametric generation/amplification of femtosecond pulses and determine the interaction geometry required to fulfill them in uniaxial crystals, The results are compared with those for collinear phase matching and are used to interpret the behavior of ultrabroadband parametric sources. (C) 1998 Optical Society of America. [References: 13]
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