  We studied the multi-plateau high-order harmonic generation (HHG) from solids
numerically. It is found that the HHG spectrum in the second or higher plateau
is redshifted in short laser pulses due to the nonadiabatic effect. The
corresponding FWHMs also increase, suggesting the step-by-step excitation
process of higher conduction bands in the HHG process. Even order harmonics in
the higher plateaus of HHG are present due to the break of symmetry in the k
space. It may stimulate related experimental work.
