Matrix elements of electron-light interactions for armchair and zigzag graphene nanoribbons are constructed analytically using a tight-binding model. The changes in wavenumber (∆n) and pseudospin are the necessary elements if we are to understand the optical selection rule. It is shown that incident light with a specific polarization and energy, induces an indirect transition (∆n = ±1), which results in a characteristic peak in the absorption spectra. Such a peak provides evidence that the electron standing wave is formed by multiple reflections at both edges of a ribbon. It is also suggested that the absorption of low-energy light is sensitive to the position of the Fermi energy, direction of light polarization, and irregularities in the edge. The effect of depolarization on the absorption peak is briefly discussed.
The dynamical modulation of the band structure of GaAs quantum wells by a surface acoustic wave ͑SAW͒ is investigated using photoluminescence ͑PL͒ spectroscopy. The strain field of the SAW modulates the excitonic transitions, leading to a splitting and to a polarization anisotropy of the excitonic PL lines. The oscillator strength of the split line gives direct information about the spatial distribution of carriers in the potential modulation induced by the SAW.
We report on photon-spin controlled lasing oscillation in GaAs surface-emitting lasers at room temperature. We demonstrate experimentally that the partial electron-spin alignment, created by optically pumping the GaAs laser active media with circularly polarized pulses, drastically changes the polarization state of the lasing output, causing circularly polarized lasing emission. We discuss the laser polarization characteristics in relation to the measured electron-spin relaxation time.
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