Quantum dot gain spectra based on harmonic oscillator model are calculated including and excluding excitons. The effects of non-equilibrium distributions are considered at low temperatures. The variations of threshold...Quantum dot gain spectra based on harmonic oscillator model are calculated including and excluding excitons. The effects of non-equilibrium distributions are considered at low temperatures. The variations of threshold current density in a wide temperature range are analyzed and the negative characteristic temperature and oscillatory characteristic temperature appearing in that temperature range are discussed. Also,the improvement of quantum dot lasers＇ performance is investigated through vertical stacking and p-type doping and the optimal dot density, which corresponds to minimal threshold current density,is calculated.展开更多
The theory model of fiber optical parametric amplifier (FOPA) was introduced, which is based on optical nonlinear effect. And then numerical simulation was done to analyze and discuss the gain spectral characteristics...The theory model of fiber optical parametric amplifier (FOPA) was introduced, which is based on optical nonlinear effect. And then numerical simulation was done to analyze and discuss the gain spectral characteristics of one-pump and two-pump FOPA. The results show that for one-pump FOPA, when pump wavelength is near to fiber zero-dispersion wavelength(ZDW), the gain flatness is better, and with the increase of the pump power, fiber length and its nonlinear coefficient, the gain value will increase while the gain bandwidth will become narrow. For two-pump FOPA, when the pump central wavelength is near to fiber ZDW, the gain flatness is better. Moreover, by decreasing the space of two pumps wavelength, the gain flatness can be improved. Finally, some problems existing in FOPA were addressed.展开更多
Monolayer FeSe films grown on SrTiO_3(STO)substrate show superconducting gap-opening temperatures(T_c) which are almost an order of magnitude higher than those of the bulk FeSe and are highest among all known Fe-based...Monolayer FeSe films grown on SrTiO_3(STO)substrate show superconducting gap-opening temperatures(T_c) which are almost an order of magnitude higher than those of the bulk FeSe and are highest among all known Fe-based superconductors. Angle-resolved photoemission spectroscopy observed ‘‘replica bands' ' suggesting the importance of the interaction between FeSe electrons and STO phonons. These facts rejuvenated the quest for T_c enhancement mechanisms in iron-based, especially ironchalcogenide, superconductors. Here, we perform the first numerically-exact sign-problem-free quantum Monte Carlo simulations to iron-based superconductors. We(1) study the electronic pairing mechanism intrinsic to heavily electron doped FeSe films, and(2) examine the effects of electron–phonon interaction between FeSe and STO as well as nematic fluctuations on T_c. Armed with these results, we return to the question ‘‘what makes the Tcof monolayer FeSe on SrTiO_3 so high?'' in the conclusion and discussions.展开更多
A deep understanding of the spectral gain characteristics of optical parametric oscillators (OPOs) and optical parametric amplifiers (OPAs) is important for a highly efficient optical parametric conversion. We numeric...A deep understanding of the spectral gain characteristics of optical parametric oscillators (OPOs) and optical parametric amplifiers (OPAs) is important for a highly efficient optical parametric conversion. We numerically calculated the spectral gain characteristics of a quasi-phase-matching (QPM) parametric conversion process using the periodically poled 6% (mol/mol) MgO doped LiNbO3 (PPMgLN) as the nonlinear crystal. In the simulation we utilized the approach of a transformative matrix of the periodically poled nonlinear medium, which results from the small-signal approximation of three-wave mixed nonlinear equations. Numerical simulation results show that: (1) The full width at half maximum (FWHM) of the spectral gain of the parametric process becomes wider with the increase of parametric wavelength and reaches the maximum at degeneration; (2) The gain coefficient decreases gradually with the increase of parametric wavelength; (3) The spectral gain bandwidth decreases correspondingly with the increase of the nonlinear material length; (4) There exists an optimal parametric wavelength band, which is most suitable for the high gain parametric conversion when pumped by a laser source with a wide wavelength band, such as the high power fiber laser.展开更多
文摘Quantum dot gain spectra based on harmonic oscillator model are calculated including and excluding excitons. The effects of non-equilibrium distributions are considered at low temperatures. The variations of threshold current density in a wide temperature range are analyzed and the negative characteristic temperature and oscillatory characteristic temperature appearing in that temperature range are discussed. Also,the improvement of quantum dot lasers＇ performance is investigated through vertical stacking and p-type doping and the optimal dot density, which corresponds to minimal threshold current density,is calculated.
文摘The theory model of fiber optical parametric amplifier (FOPA) was introduced, which is based on optical nonlinear effect. And then numerical simulation was done to analyze and discuss the gain spectral characteristics of one-pump and two-pump FOPA. The results show that for one-pump FOPA, when pump wavelength is near to fiber zero-dispersion wavelength(ZDW), the gain flatness is better, and with the increase of the pump power, fiber length and its nonlinear coefficient, the gain value will increase while the gain bandwidth will become narrow. For two-pump FOPA, when the pump central wavelength is near to fiber ZDW, the gain flatness is better. Moreover, by decreasing the space of two pumps wavelength, the gain flatness can be improved. Finally, some problems existing in FOPA were addressed.
基金the National Supercomputer Center in Guangzhou for computational supportZXL and HY were supported in part by the National Thousand Young-Talents Program and the National Natural Science Foundation of China (11474175)+1 种基金FW was supported by the National Natural Science Foundation of China (11374018)DHL was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division, Grant DE-AC0205CH11231
文摘Monolayer FeSe films grown on SrTiO_3(STO)substrate show superconducting gap-opening temperatures(T_c) which are almost an order of magnitude higher than those of the bulk FeSe and are highest among all known Fe-based superconductors. Angle-resolved photoemission spectroscopy observed ‘‘replica bands' ' suggesting the importance of the interaction between FeSe electrons and STO phonons. These facts rejuvenated the quest for T_c enhancement mechanisms in iron-based, especially ironchalcogenide, superconductors. Here, we perform the first numerically-exact sign-problem-free quantum Monte Carlo simulations to iron-based superconductors. We(1) study the electronic pairing mechanism intrinsic to heavily electron doped FeSe films, and(2) examine the effects of electron–phonon interaction between FeSe and STO as well as nematic fluctuations on T_c. Armed with these results, we return to the question ‘‘what makes the Tcof monolayer FeSe on SrTiO_3 so high?'' in the conclusion and discussions.
基金supported by the National Natural Science Foundation of China (No. 60778001)the National Basic Research Program (973) of China (No. 2007CB307003)
文摘A deep understanding of the spectral gain characteristics of optical parametric oscillators (OPOs) and optical parametric amplifiers (OPAs) is important for a highly efficient optical parametric conversion. We numerically calculated the spectral gain characteristics of a quasi-phase-matching (QPM) parametric conversion process using the periodically poled 6% (mol/mol) MgO doped LiNbO3 (PPMgLN) as the nonlinear crystal. In the simulation we utilized the approach of a transformative matrix of the periodically poled nonlinear medium, which results from the small-signal approximation of three-wave mixed nonlinear equations. Numerical simulation results show that: (1) The full width at half maximum (FWHM) of the spectral gain of the parametric process becomes wider with the increase of parametric wavelength and reaches the maximum at degeneration; (2) The gain coefficient decreases gradually with the increase of parametric wavelength; (3) The spectral gain bandwidth decreases correspondingly with the increase of the nonlinear material length; (4) There exists an optimal parametric wavelength band, which is most suitable for the high gain parametric conversion when pumped by a laser source with a wide wavelength band, such as the high power fiber laser.
