Theory of terahertz intervalence band polaritons and antipolaritons.

The work presented in this thesis is a theoretical investigation of the interaction of terahertz (THz) radiation with intersubband excitations in microcavities leading to THz polaritons and antipolaritons. The approach is based on the dielectric function formalism. The dielectric constant is derived from an optical susceptibility evaluated with Non Equilibrium Many Body Green's Functions (NEGF), which is then adjusted to a Lorentzian fit. Finally, the resulting expression is included in the wave equation describing the propagating electric field in the medium. This model is applied to GaAs/Al[0.3]Ga[0.7]As multiple quantum wells embedded in a microcavity. The energy dispersion relations leading to THz polaritons and antipolaritons are obtained and investigated for different carrier densities and cavity configurations. Recently, intersubband based THz polariton emitters and THz quantum cascade lasers are attracting major research interest due to their great importance in applications such as THz imaging, spectroscopy as well as in security control for detection of biological and hazardous materials and medical diagnosis. The coupling of THz radiation with intersubband transitions in semiconductor microcavities can lead to further tunability and improved quantum efficiency for THz devices. Here we propose a simple geometry and used a simplified modelling technique to investigate the interactions of transverse electric (TE-Mode) polarized THz cavity modes with intervalence band excitations. The model is applied to single and multiple transition problems and combinations of many body effects and scattering mechanism are included in the input dielectric constant

Nonlinear intersubband THz absortion in asymmetric quantum well structures

"Semiconductor devices are a very important sou.rce Of electromagnetic (ENI) waves daily life applications. In one extreme; the, visible and infrared (IR) Insers are at the core of informntion technology. In the Other, microwave and radio frequency elliitt,ers make possible wireless communications. But in the THz region of the EM spectrum, thai spans from 100GHz to 10THz, there is an scarcity of compact solid-state sources thai operate at room temperature. But in present times there is a need for such devices as a relatively long list of applications has been envisioned for the THz range: chernical detection, astronomy, wireless communications, atmospheric sensing, dental, biological and medical imaging are among the possible applications for this region. Another set of interesting experiments in the T Hz range are t,he Tllz Time Domain Spectroscopy (TH' TDS) experirnents. These works are illipoñant in both fundarnental research and realworld applications..."-- Tomado de la Introducción.Magíster en FísicaMaestrí