20 research outputs found
Time-resolved linewidth and lineshape measurements of a pulsed optically pumped far infrared D2O laser
Effect of fermionic components on trion-electron scattering
To test the validity of replacing a composite fermion by an elementary
fermion, we here calculate the transition rate from a state made of one free
electron and one trion to a similar electron-trion pair, through the time
evolution of such a pair induced by Coulomb interaction between elementary
fermions. To do it in a convenient way, we describe the trion as one electron
interacting with one exciton, and we use the tools we have developed in the new
composite-exciton many-body theory. The trion-electron scattering contains a
direct channel in which ``in'' and ``out'' trions are made with the same
fermions, and an exchange channel in which the ``in'' free electron becomes one
of the ``out'' trion components. As expected, momenta are conserved in these
two channels. The direct scattering is found to read as the bare Coulomb
potential between elementary particles multiplied by a form factor which
depends on the ``in'' and ``out'' trion relative motion indices and
, this factor reducing to in the zero momentum
transfer limit: In this direct channel, the trion at large distance reacts as
an elementary particle, its composite nature showing up for large momentum
transfer. On the contrary, the fact that the trion is not elementary does
affect the exchange channel for all momentum transfers. We thus conclude that a
3-component fermion behaves as an elementary fermion for direct processes in
the small momentum transfer limit only
Fresnel polarisation of infra-red radiation by elemental bismuth
We revisit the classical problem of electromagnetic wave refraction from a lossless dielectric to a lossy conductor, where both media are considered to be non-magnetic, linear, isotropic and homogeneous. We derive the Fresnel coefficients of the system and the Poynting vectors at the interface, in order to compute the reflectance and transmittance of the system. We use a particular parametrisation of the referred Fresnel coefficients so as to make a connection with the ones obtained for refraction by an interface between two lossless media. This analysis allows the discussion of an actual application, namely the Fresnel polarisation of infra-red radiation by elemental bismuth, based on the concept of pseudo Brewsterâs angle.We acknowledge helpful discussions with M. Vasilevskiy, P. Alpuim, J. Caridad and B. Figueiredo. The authors thank the European Structural and Investment Funds in the FEDER component, through the Operational Programme for Competitiveness and Internationalization (COMPETE 2020) [under the Project GNESIS -Graphenest's New Engineered System and its Implementation Solutions; Funding Reference: POCI-01-0247-FEDER-033566], European Regional Development Fund. This work was also supported by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding UID/FIS/04650/2019