  We show that simple models of scalar-field dark energy leave a generic
enhancement in the weak-lensing power spectrum when compared to the LCDM
prediction. In particular, we calculate the linear-scale enhancement in the
convergence (or cosmic-shear) power spectrum for two best-fit models of
scalar-field dark energy, namely, the Ratra-Peebles and SUGRA-type
quintessence. Our calculations are based on linear perturbation theory, using
gauge-invariant variables with carefully defined adiabatic initial conditions.
We find that geometric effects enhance the lensing power spectrum on a broad
range of scales, whilst the clustering of dark energy gives rise to additional
power on large scales. The dark-energy power spectrum for these models are also
explicitly obtained. On degree scales, the total enhancement may be as large as
30-40% for sources at redshift ~1. We argue that there are realistic prospects
for detecting such an enhancement using the next generation of large
telescopes.
