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Pillay J.C.,Nanyang Technological University | Natsume Y.,Nanyang Technological University | Stone A.D.,Yale University | Chong Y.D.,Nanyang Technological University | Chong Y.D.,Center for Disruptive Photonic Technologies
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2014

A recent S-matrix-based theory of the quantum-limited linewidth, which is applicable to general lasers, including spatially nonuniform laser cavities operating above threshold, is analyzed in various limits. For broadband gain, a simple interpretation of the Petermann and bad-cavity factors is presented in terms of geometric relations between the zeros and poles of the S matrix. When there is substantial dispersion, on the frequency scale of the cavity lifetime, the theory yields a generalization of the bad-cavity factor, which was previously derived for spatially uniform one-dimensional lasers. This effect can lead to sub-Schawlow-Townes linewidths in lasers with very narrow gain widths. We derive a formula for the linewidth in terms of the lasing mode functions, which has accuracy comparable to the previous formula involving the residue of the lasing pole. These results for the quantum-limited linewidth are valid even in the regime of strong line pulling and spatial hole burning, where the linewidth cannot be factorized into independent Petermann and bad-cavity factors. © 2014 American Physical Society.

Zhan D.,Research Institute for Soft Matter and Biomimetics | Zhan D.,Center for Disruptive Photonic Technologies | Yan J.X.,Center for Disruptive Photonic Technologies | Ni Z.H.,Nanjing Southeast University | And 5 more authors.
Small | Year: 2015

Graphene is a kind of novel two dimensional material and considered as a potential candidate for nanoelectronics owing to its exotic electronic properties, such as Massless Dirac Fermions, room-temperature quantum Hall effect, Berry phase and Klein tunneling. Raman spectroscopy has become a powerful tool to characterize graphene-based materials, including identifying number of layers, doping, defects, stacking, strain and edges, in particular, the thickness and stacking sequence along z-direction can also be identified accurately. Therefore, the proposed conception of the asymmetric intercalation of grapheme induced interesting phenomenon is not only limited to trilayer case, but also available for quad-layer, and it is deserved for further studies in future. To date, it is still a challenge because that the molecular dynamics for intercalation process is still unclear though it has been investigated for more than 40 years.

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