Population inversion in optically pumped asymmetric quantum well terahertz lasers
Intersubband carrier lifetimes and population ratios are calculated for three- and four-level optically pumped terahertz laser structures. Laser operation is based on intersubband transitions between the conduction band states of asymmetric GaAs-Ga1−xAlxAs quantum wells. It is shown that the carrier lifetimes in three-level systems fulfill the necessary conditions for stimulated emission only at temperatures below 200 K. The addition of a fourth level, however, enables fast depopulation of the lower laser level by resonant longitudinal optical phonon emission and thus offers potential for room temperature laser operation.
Intersubband transitions from the second subband in a coupled quantum wells structure
Abstract Asymmetrical coupled quantum wells structures with energy separation between the first two subbands of the order of 10–50 meV are key structures in the design of optically pumped intersubband lasers. In these structures the population of the second subband is not negligible and intersubband transitions from the second to higher excited subbands can be observed. In this work we investigate the temperature dependency of the intersubband transitions from the second subband in an asymmetrical coupled quantum wells structure. We show that this approach provides a direct way to measure the energy separation between the second subband and the Fermi energy which is a crucial parameter in the design of optically pumped intersubband lasers.
Microscopic theory of enhanced nonlinear refraction in semiconductor superlattices.
On montre qu'un choix realiste de parametres structuraux peut etre fait pour generer des susceptilites de plusieurs ordres de grandeur superieurs a ceux rapportes pour des materiaux massifs. Les estimations fondees sur des methodes approximatives surestiment significativement la force de la reponse non lineaire