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Freezing the carrier-envelope phase of few-cycle light pulses about a focus.

We study the effects of dispersive media and structures on the carrier-envelope phase (CEP) shift of focused few-cycles pulses. For phase-sensitive interactions with matter requiring focusing in vacuum, the variation of the CEP through the focal region can be significantly slow down by inserting a dispersive slab of adequate thickness between the focusing system and the focus. The focal CEP shift can also be slow down in experiments requiring focusing in a dispersive medium by a suitable choice of the dispersive propagation distance up to the focus.