In this work we address the phonon-polariton band gap study in periodic and quasi-periodic (Fibonacci-type)
multilayers made up of both positive (SiO2) and negative refractive index materials (metamaterials) following
the Fibonacci sequence in the terahertz region. The behavior of the polaritonic band gaps as a function of the
multilayer period is investigated. Our theoretical model makes use of a transfer matrix approach to simplify
the algebra involved and to set up analytical phonon-polariton dispersion relations (bulk and surface modes).
We also present a quantitative analysis of the results, pointing out the distribution of the allowed polaritonic
bandwidths for high Fibonacci generations. An analysis of the connement eects arising from the competition
between the long-range aperiodic order, induced by the quasi-periodic structure, and the short-range disorder,
are made, yielding a good insight about they localization and power law of the polaritonic modes.
We have calculated the optical gain in unstrained graded GaAs/AlxGal-xAs single quantum well lase4rs as a function of the energy of the radiation and the interface widths. The calculation of the electronic structure was done using the parabolic band model, while the valence band structure was determined taking into account the effects of the sub-band mixing between the heavy and light holes. The optical gain was calculated using the density matrix approach, considering all sub-band transitions in the quantum well the transversal electrical (TE mode) light polarization. Our results show that the peak gain is sensitive to the width and the graded profile of the interfaces, and the gain spectrum is blue-shifted as a function of the interface width.
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