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Room temperature Terahertz stimulated emission and population inversion inoptically pumped graphene is reported. We experimentally observe fastrelaxation and relatively slow recombination dynamics of photogeneratedelectrons/holes in an exfoliated graphene on SiO2/Si substrate under pumpingwith a 1550-nm, 80-fs pulsed fiber laser beam and probing with thecorresponding terahertz beam generated by optical rectification in a nonlinearelectro optical sensor. The time resolved electric field intensity originatingfrom the coherent terahertz photon emission is electro-optically sampled in antotal-reflection geometry. The comparison of terahertz electric fieldsintensities measured on SiO2/Si substrate and that one from graphene clearlyindicate that graphene sheet act like an amplifying medium. The Emissionspectra agrees relatively well the pumping photon spectrum and its dependencyon the pumping power shows a threshold like behavior, testifying the occurrenceof the negative conductivity in the THz spectral range and the populationinversion. The threshold pumping intensity > 5*10^6 W/cm^2 is in a goodagreement with simulations.

Amplified Stimulated Terahertz Emission at Room temperature from Optically Pumped Graphene