# Generalized Kirchhoff law

@article{Greffet2016GeneralizedKL, title={Generalized Kirchhoff law}, author={Jean-Jacques Greffet and Patrick Bouchon and Giovanni Brucoli and Emilie Sakat and Franccois Marquier}, journal={arXiv: Optics}, year={2016} }

Thermal emission can be conveniently described using Kirchhoff law which states that the emissivity is equal to the absorptivity for isothermal bodies. For a finite size system, absorptivity is replaced by an absorption cross section. Here, we study the link between thermal emission and absorption by a finite size object which is not isothermal. We define a local absorption rate for a given incident plane wave and we prove that it is equal to the local emissivity rate. Hence, Kirchhoff law can…

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