Dipole nanolaser

A “dipole” laser is proposed consisting of a nanoparticle and a two-level system with population inversion. If the threshold conditions are fulfilled, the dipole interaction between the two-level system and the nanoparticle leads to coherent oscillations in the polarization of the particles, even in the absence of an external electromagnetic field. The emitted radiation has a dipolar distribution. It does not need an optical cavity, and has a very small volume, $\sim 0.1\mu {\mathrm{m}}^3$, which can be important for applications in microelectronics. Estimates of the threshold conditions are carried out for a dipole laser composed of a quantum dot and a silver nanoparticle.

Figure 1

Scheme of dipole nanolaser. Parameters of the nanoparticle have index 0, parameters of the two-level system have index 2.

Figure 2

Dimensionless distance $\xi$ between the TLS and the nanoparticle as a function of temperature. The necessary condition for dipole lasing is $\xi >0$. The dipole approximation used in our estimates is valid if $\xi ⪢1$. The solid line assumes ${ϵ}^{″}\sim T$, the dashed line uses the $T=300\mathrm{K}$ value of ${ϵ}^{″}=5.74$.

Figure 3

Schematic of different approaches to achieve overlapping polarizabilities for dipole nanolaser; 2 indicates two-level system, 0 the nanoparticle. Dashed curves reflect the values of the polarizabilities, the solid curves show the geometrical size of the particles.