PUB - Publikationen an der Universität Bielefeld

We consider a new class of massless charged relativistic quasi-particles associated with low-energy excitations in graphene, interacting with an intense electromagnetic field and obtain the adiabatic solutions of the corresponding time-dependent Dirac equation. The solutions are used to investigate emission of high harmonic radiation by such quasi-particles in strong long-wavelength lasers. The emitted harmonic spectrum is found to exhibit a remarkably high relative intensity extending over large harmonic orders, and are characterized by intensity 'revivals' and 'plateaus'. We also briefly consider high harmonic emissions from excitations of an entire band of a graphene sheet which show a different emission spectrum with an exponential fall off above a cutoff order n(cutoff) = omega(B)/omega, where omega(B) = eF(0)b/h h is the Bolch frequency. These characteristics of the high harmonic emission spectra from only the low-energy excitations (so-called graphinos), and/or from the excitations of the whole band of a graphene layer, would be interesting to observe in possible future experiments.