普朗克定律的推广：激发介质的非平衡发射
Generalizing Planck's Law: Nonequilibrium Emission of Excited Media
摘要：
利用量子动力学多体方法，给出了特定几何条件下场与物质相互作用系统的精确结果。结果表明，光子的光谱函数和场的波动分裂成真空和介质诱导的贡献，推导出明确的表达式。利用坡印廷定理，分析了非相干发射，并将其与可以在线性透射-反射实验中测量的相干吸收联系起来。它们的比率定义了横向电磁场模式的介质诱导的布居，因此将普朗克定律推广到非平衡稳态中的任意吸收和色散介质。对于准平衡，这个人口发展成玻色分布，其化学势标志着从吸收到增益的交叉，也表征了激发的程度。在此基础上讨论了激光和量子凝聚等宏观量子现象。
英文摘要：
Using a quantum-kinetic many-body approach, exact results for the interacting system of field and matter in a specified geometry are presented. It is shown that both the spectral function of photons and the field fluctuations split up into vacuum- and medium-induced contributions, for which explicit expressions are derived. Using Poynting's theorem, the incoherent emission is analyzed and related to the coherent absorption as may be measured in a linear transmission-reflection experiment. Their ratio defines the medium-induced population of the modes of the transverse electromagnetic field and so generalizes Planck's law to an arbitrarily absorbing and dispersing medium in a nonequilibrium steady state. For quasi-equilibrium, this population develops into a Bose distribution whose chemical potential marks the crossover from absorption to gain and, also, characterizes the degree of excitation. Macroscopic quantum phenomena such as lasing and quantum condensation are discussed on this footing.
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