Two-Photon Lasers Based on Intersubband Transitions in Semiconductor Quantum Wells

We propose to make a two-photon laser based on intersubband (sublevel) transitions in semiconductor nanostructures. The advantages and feasibility of such a two-photon laser are analyzed in detail using the density matrix approach. Both one-photon and two-photon gains in a three subband quantum well structure are studied on the same footing to show how the two-photon gain can be maximized, while the competing one-photon gain is minimized. The results show that a sufficient two-photon gain can be achieved to overcome one-photon competition and the loss of a conventional semiconductor cavity, making intersubband transitions one of the very few feasible approaches to two-photon lasing.

Figure 1

$G_1$ (solid line) and $G_2$ (dash-dotted line) as a function of the one-photon detuning in a quantum well structure as depicted in the inset. Other parameters are given in the figure $N_p=2\sum _k{f}_{pk}/V$.

Figure 2

Optical gain and gain ratio as a function of the one-photon detuning for various probe power levels as given in the top panel, marked, respectively, by $1$ through $4$ in the increasing order.

Figure 3

$G_1$ (solid line) and $G_2$ (dash-dotted line) as functions of the probe field power as $\delta$ is increased from one through five in the order indicated by the arrow. The inset shows the enlarged section where $G_2$ overtakes $G_1$. The crossing point at each detuning is marked by a circle.