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Ultrafast energy absorption and photoexcitation of bulk plasmon in crystalline silicon subjected to intense near-infrared ultrashort laser pulses
摘要： We investigate the non-linear response and energy absorption in bulk silicon irradiated by intense 12-fs near-infrared laser pulses. Depending on the laser intensity, we distinguish two regimes of non-linear absorption of the laser energy: for low intensities, energy deposition and photoionization involve perturbative three-photon transition through the direct bandgap of silicon. For laser intensities near and above 1014 W/cm2, corresponding to photocarrier density of order 1022 cm?3, we find that absorption at near-infrared wavelengths is greatly enhanced due to excitation of bulk plasmon resonance. In this regime, the energy transfer to electrons exceeds a few times the thermal melting threshold of Si. The optical reflectivity of the photoexcited solid is found in good qualitative agreement with existing experimental data. In particular, the model predicts that the main features of the reflectivity curve of photoexcited Si as a function of the laser fluence are determined by the competition between state and band filling associated with Pauli exclusion principle and Drude free-carrier response. The non-linear response of the photoexcited solid is also investigated for irradiation of silicon with a sequence of two strong and temporary non-overlapping pulses. The cumulative effect of the two pulses is non-additive in terms of deposited energy. Photoionization and energy absorption on the leading edge of the second pulse is greatly enhanced due to free carrier absorption.
关键词： bulk silicon,optical reflectivity,photoexcited solid,near-infrared laser pulses,Drude free-carrier response,non-linear response,energy absorption,plasmon resonance
更新于2025-09-23 15:21:01
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AIP Conference Proceedings [AIP Publishing 15th International Conference on Concentrator Photovoltaic Systems (CPV-15) - Fes, Morocco (25–27 March 2019)] 15th International Conference on Concentrator Photovoltaic Systems (CPV-15) - Averaging the unaverageable: Defining a meaningful local series resistance for large-area silicon solar cells
摘要： From its definition based on lateral voltage drops, the local series resistance isn’t an arithmetically averageable quantity because voltage isn’t extensive; however, only such quantities can be averaged. Still, empirically it was found that averaging series images arithmetically provides rather reasonable results. Since the emitter of a large-area silicon solar cell is nearly an equipotential layer, one can linearize the description of the lateral voltage distribution (with respect to the forward-bias current and the emitter resistivity), from which we obtain an averageable local series resistance for the H-type grid geometry; its averageability stems from averaging the parallel paths of vertical current flow. By construction, the average obtained from this linear response theory is identical to the lumped value coming from the illumination intensity variation method, and it also shows the experimentally observed dependency on the forward-bias diode current.
关键词： local series resistance,linear response theory,arithmetic averaging,illumination intensity variation method,silicon solar cells
更新于2025-09-16 10:30:52
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Optical conductivity and transparency in an effective model for graphene
摘要： Motivated by experiments confirming that the optical transparency of graphene is defined through the fine structure constant and that it could be fully explained within the relativistic Dirac fermions in a two-dimensional picture, we investigate in this article how this property is affected by next-to-nearest-neighbor coupling in the low-energy continuum description of graphene. A detailed calculation within the linear response regime allows us to conclude that, somewhat surprisingly, the optical conductivity at zero temperature that determines the transparency remains robust up to this correction.
关键词： graphene,optical conductivity,linear response,transparency,Dirac fermions
更新于2025-09-10 09:29:36
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Bipolar Thermoelectric Effects in Semiconducting Carbon Nanotubes: Description in Terms of One-Dimensional Dirac Electrons
摘要： The thermoelectric effects in semiconducting single-walled carbon nanotubes (SWCNTs) are investigated based on the linear response theory combined with the thermal Green’s function method. It is shown that the electronic states near the lowest conduction band minimum and the highest valence band maximum can be effectively described in terms of one-dimensional (1D) Dirac electrons to which a theoretical scheme is developed to describe the thermoelectric responses making it possible to study the effects of inter-band impurity scattering and in-gap states. Using the proposed scheme, the bipolar thermoelectric effects (i.e., the sign inversion of the Seebeck coefficient) in semiconducting SWCNTs observed in recent experiments are explained. Moreover, the temperature dependence of the Seebeck coefficient of semiconducting SWCNTs at low temperature is clarified.
关键词： thermal Green’s function method,Seebeck coefficient,linear response theory,Dirac electrons,semiconducting single-walled carbon nanotubes,thermoelectric effects
更新于2025-09-04 15:30:14