  We studied dependence of dissociative ionization in H2 on carrier-envelope
phase (CEP) of few-cycle (6fs) near-infrared (NIR) laser pulses. For low-energy
channels, we present the first experimental observation of CEP dependence for
total dissociation yield and the highest dwgree of asymmetry reported to date
(40%). The observed modulations in both asymmetry and total yield could be
understood in terms of interference between different n-photon dissociation
pathways - n and (n+1) photon channels for asymmetry, n and (n+2) photon
channels for yield - as suggested by the general theory of CEP effects (Roudnev
and Esry, Phys. Rev. Lett. 99, 220406 (2007), [1]). The yield modulation is
found to be Pi-periodic in CEP, with its phase strongly dependent on fragment
kinetic energy (and reversing its sign within the studied energy range),
indicating that the dissociation does not simply follow the CEP dependence of
maximum electric field, as a naive intuition might suggest. We also find that a
positively chirped pulse can lead to a higher dissociation probability than a
transform limited pulse.
