  Coherent one photon ($2 \omega$) and two photon ($ \omega$) electronic
excitations are studied for graphene sheets and for carbon nanotubes using a
long wavelength theory for the low energy electronic states. For graphene
sheets we find that coherent superposition of these excitations produces a
polar asymmetry in the momentum space distribution of the excited carriers with
an angular dependence which depends on the relative polarization and phases of
the incident fields. For semiconducting nanotubes we find a similar effect
which depends on the square of the semiconducting gap, and we calculate its
frequency dependence.
  We find that the third order nonlinearity which controls the direction of the
photocurrent is robust for semiconducting t ubes and vanishes in the continuum
theory for conducting tubes. We calculate corrections to these results arising
from higher order crystal field effects on the band structure and briefly
discuss some applications of the theory.
