Characteristics of induced radiation under the action of short high-frequency pulses on graphene

Background and Objectives: The nonlinear effects of high-harmonic generation in various materials provide new tools for studying ultrafast electron dynamics and open up a possible way to create coherent light sources in currently inaccessible frequency ranges. Graphene is regarded as one of the most promising materials for these purposes. To describe nonlinear processes in it, it is necessary to be able to reproduce the change in the population of electronic states in the conduction band under the action of an intense external electric field and the effects observed in this case. Materials and Methods: The work is devoted to demonstrating the applicability of the quantum kinetic equation method and the software solution developed on its basis for these purposes. The implemented approach provides an accurate reproduction of the response of the electronic subsystem of the material to an external pulse action in a wide range of frequencies, durations and strength of the field. The characteristics of the plasma field accessible to an external observer are reproduced and analyzed. The method allows considering various initial states of the model. This can be a vacuum state with a complete absence of electrons in the conduction band or an equilibrium distribution of carriers at a given temperature. The use of the relaxation time approximation in the kinetic equation makes it possible to estimate the influence of dissipative processes on the behavior of the model. Results: The demonstration was carried out on the example of modeling the observed effects of a short infrared pulse on a graphene monolayer and comparing the results with experimental data. The presented results have been obtained for a version of the kinetic equation defined in the massless fermion approximation. The reproduction of the high-harmonic generation effect has been confirmed. The effect of the electron-hole plasma relaxation on the simulated results has been demonstrated. The processes of intraband carrier dynamics and interband transitions under the influence of an external electric field have been singled out and available for separate analysis. The dependence of the high-harmonic generation effect on the type of polarization of the external pulse field has been demonstrated. Conclusion: The presented results have been the applicability of the developed method and its software implementation for modeling the generation of higher harmonics under the conditions of nonlinear interaction of graphene with external high-frequency fields. The method works in a wide range of sample and external field parameters.