Electric Spaser in the Extreme Quantum Limit

We consider theoretically the spaser that is excited electrically via a nanowire with ballistic quantum conductance. We show that, in the extreme quantum regime, i.e., for a single conductance-quantum nanowire, the spaser with a core made of common plasmonic metals, such as silver and gold, is fundamentally possible. For ballistic nanowires with multiple-quanta or nonquantized conductance, the performance of the spaser is enhanced in comparison with the extreme quantum limit. The electrically pumped spaser is promising as an optical source, nanoamplifier, and digital logic device for optoelectronic information processing with a speed of $\sim 100\mathrm{GHz}$ to $\sim 100\mathrm{THz}$.

Figure 1

For three plasmonic metals, Ag, Au, and Al, we show the dependencies of the working parameters of the cw-regime spaser on the spasing frequency ${\omega }_n$ expressed as the corresponding SP energy $\hslash \omega$. (a) Mean number of SPs per spasing mode $N_n$ in the extreme quantum limit, computed from Eq. (5) for a single-conduction quantum channel, $N_c=1$. (b) Threshold gain $g_{\mathrm{th}}$ required for spasing as computed from Eq. (6). (c) The nanowire current required for developed spasing with a single SP quantum per the spasing mode for the three plasmonic metals, as indicated (solid lines). The current of the single-channel QW under the minimum required potential difference is shown by the dashed line. Developed spasing is possible for the spectral regions where the corresponding $J_{\mathrm{QW}}$ curves are below this line.