Competing Inversion-Based Lasing and Raman Lasing in Doped Silicon

Abstract

We report on an optically pumped laser where photons are simultaneously generated by population inversion and by stimulated Raman scattering in the same active medium, namely crystalline silicon doped by bismuth (Si∶Bi). The medium utilizes three electronic levels: ground state [|1⟩: 1s(A_{1}) in Si∶Bi], upper [|3⟩: 2p_{±}] and lower [|2⟩: 1s(E)] laser levels. The |1⟩↔|3⟩ and |2⟩↔|3⟩ transitions are optically allowed and the |1⟩↔|2⟩ transition is Raman active. Lasing based on population inversion occurs between the states |3⟩ and |2⟩, while Raman scattering benefits from the Raman-active transition. At high pump power the inversion-based stimulated emission |3⟩→|2⟩ disappears, because electronic scattering from |1⟩ to |2⟩ via a virtual state dominates and the electrons are excited into |2⟩ rather than into |3⟩. Starting as population inversion-based lasing, it ends as stimulated Raman scattering. Our model shows that such a competition occurs on the timescale of the 10-ps-long pump pulse.