We propose and substantiate the concept of terahertz (THz) laser based on the optically pumped graphene layers and the resonant cavity of the Fabri-Perot type. The pumping scheme which corresponds to the optical interband excitation of graphene followed by the emission of an optical phonons cascade provides the population inversion for the interband transitions in a relatively wide range of THz frequencies. We demonstrate that the THz lasing in the device under consideration at room temperatures is feasible if its structure is optimized. The frequency and output power of the generated THz radiation can be tuned by varying the distance between the mirrors.
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