有限温度下线性谐振子晶格的分子动力学模拟

基于双向界面条件和声子热浴,提出了一种新的热流输入方法,该方法未引入任何耗散因子或经验参数,能在局域的空间和时间上实现有限温度下的原子模拟.对于一维线性谐振子晶格,采用双向界面条件作为系统的边界,目的是为了让热流能从外界输入系统,同时允许内部的波动自由地传出,从而实现系统中能量的动态平衡.通过数值计算发现,双向界面条件能让正方向的波完整地输入,同时还能抑制反方向的波的输入,因此,边界条件可以起到行波的二极管的作用.声子热浴的正则模态能很好地描述原子的热振动,通过推导可将正则模态分解为正方向和反方向的输入波,取正方向的波来构造热源项.数值算例表明,热流输入方法对于线性谐振子链非常有效,系统能快速地达到预期的温度,并且能够维持在稳定的状态,同时,还能很好地处理有限温度下的非热运动.     

Research of the use of silver nanowires as a current spreading layer on vertical-cavity surface-emitting lasers

Silver nanowire(AgNW) film was proposed to apply on the surface of the vertical-cavity surface-emitting lasers(VCSELs) with large aperture in order to obtain a uniform current distribution in the active region and a better optical beam quality.Optimization of the AgNW film was carried out with the sheet resistance of 28.4 Ω/sq and the optical transmission of 94.8% at 850 nm.The performance of VCSELs with and without AgNW film was studied.When the AgNW film was applied to the surface of VCSELs,due to its better current spreading effect,the maximum output optical power increased from 23.4 mW to 24.4 mW,the lasing wavelength redshift decreased from 0.085 nm/mA to 0.077 nm/mA,the differential resistance decreased from 23.95 Ω to 21.13 Ω,and the far field pattern at 50 mA decreased from 21.6° to 19.2°.At the same time,the near field test results showed that the light in the aperture was more uniform,and the far field exhibited a better single peak characteristic.Various results showed that VCSELs with AgNW on the surface showed better beam quality.