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Theses

Etude de l'émission spontanée dans des structures à
cascade quantique en microcavité métallique

Abstract : The subject of this PhD work is the manifestation of the Quantum Electrodynamics in a Cavity (QED) effects in the THz domain. The THz domain is defined as the frequency region between 300 GHz and
30 THz (in terms of wavelength: between 10 µm and 1000 µm). The sources that we use to generate the THz radiation are electroluminescent GaAs/AlGaAs quantum cascades.

The radiated wavelength (l ~ 100 µm) is much larger than the typical thickness of the quantum cascade (~1 µm). Therefore, when the source is inserted into à planar metallic cavity, the spontaneous emission rate increases as the inverse of the cavity thickness.

A part of the PhD work is a theoretical analysis of the devices in a cavity. The spontaneous emission rate is studied both from the classical point of view, in terms of retro-reflected field, and
from a quantum-mechanical point of view, in terms of the Fermi golden rule. For the latter, we have developed a numerical method for the calculation and normalization of modes supported by an
arbitrary multilayered system, that can be applied in lasing regime. The study of sub-wavelength cavities allows to distinguish between an "useful" effect, concerning the fundamental guided
TM_0 mode, from an absorption effect of the spontaneous emission rate, that occurs because of the surface plasmon that exist into the doped contact layers, employed for current injection into the quantum cascade structure.

We further analyse the luminescence extraction from the cavity. For this purpose, we study a photonic device of a new type, "a complex cavity", in which the upper metallic mirror is replaced by a metallic grating. A general model of conical diffraction is developed for these studies. The model has been confirmed in transmission measurements in the THz domain. It has been applied to the case of a dipole source inside a complex cavity. The variation of the extracted power as function of the cavity
thickness and the grating period are related to the QED effects on the spontaneous emission.

In order to obtain an experimental proof of the QED effects in the THz domain, we have fabricated and studied complex metallic cavities with a quantum cascade. The MOCVD epitaxial growth, so
far fairy unexplored for THz quantum cascades, has been optimised with the possibility of growing laser devices. Our experimental studies confirm the theory. A spontaneous emission enhancement
factor of ~ 50 has been deduced for the thinnest device 0.4 µm. This is the first time the QED effect of spontaneous emission enhancement by reducing the device thickness has been put into evidence in the THz domain.

As possible further development is the reducing the lateral size of the device to obtain a full 3D Purcell effect. Also, the surface plasmon of the doped layers can be exploited for the conception of compact THz photonic devices of a new kind.
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Contributor : Yanko Todorov <>
Submitted on : Friday, January 19, 2007 - 3:00:03 PM
Last modification on : Thursday, December 10, 2020 - 2:25:52 PM
Long-term archiving on: : Tuesday, April 6, 2010 - 7:55:49 PM

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  • HAL Id : tel-00125437, version 1

Citation

Yanko Todorov. Etude de l'émission spontanée dans des structures à
cascade quantique en microcavité métallique. Physique Atomique [physics.atom-ph]. Université Pierre et Marie Curie - Paris VI, 2006. Français. ⟨tel-00125437⟩

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