  We obtain a class of adiabatic solutions of Dirac equation for the charged
massless relativistic quasi-particles that arise from the low-energy
excitations \cite{foot-1} in a 2D graphene sheet, interacting with an
electromagnetic field. The analytic solutions obtained are useful for {\it
non-perturbative} investigation of processes in intense laser fields. As a
first example we employ them to predict copious emissions of high order
harmonics by THz lasers interacting with the occupied states of graphinos in
the vicinity of the degenerate Dirac points. The relative intensity of the
emitted harmonics is seen to decrease by only about two orders of magnitude
from the 3rd to the 81st harmonic order, and is characterized by two phenomena
of "revival" and "plateau" formation in the middle and the far end of the
spectrum calculated. A preliminary comparison is made for harmonic emission
from 2D graphene that reveals a qualitatively different spectrum in the latter
case showing a sharp cutoff at an order $n_{cutoff} = \frac{\omega_B}{\omega}$
where $\omega_B=eF_0b/\hbar$ is the so-called Bloch frequency.
