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.