  We investigate the high harmonic generation (HHG) in solids driven by laser
fields with different ellipticities. The HHG spectra show a two-plateau
structure within the energy gap between the valence band and the first
conduction band. These two plateaus depend distinctly on the laser ellipticity.
The first plateau is decreased while the second plateau is enhanced with
increasing the laser ellipticity. To understand these phenomena, we develop an
intuitive Reciprocal-Space- Trajectory (RST) method, with which HHG in solids
is explained by a trajectory-ensemble from different initial states and
different ionization times in the reciprocal space. In the framework of RST, we
can not only quantitatively reproduce the HHG spectra, but also well understand
the underlying physics of these phenomena, providing a deep insight into the
mechanism of HHG in solids.
