Mechanism of transient population inversion in graphene with multi-split (interdigitated) top-gate and grounded back gate is suggested and examined for the mid-infrared spectral region. Efficient stimulated emission after fast lateral spreading of carriers due to drift-diffusion processes is found for the case of a slow electron-hole recombination in the passive region. We show that with the large gate-to-graphene distance, the drift process always precedes the diffusion process, due to the ineffective screening of the inplane electric field by the gates. Conditions for lasing with a gain above 100 cm-1 are found for cases of single- and multi-layer graphene placed in the waveguide formed by the top and back gates. Both the waveguide losses and temperature effects are analysed.
- mid-infrared laser
- population inversion