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2017 ; 114
(17
): 4336-4341
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Universal modal radiation laws for all thermal emitters
#MMPMID28396436
Miller DAB
; Zhu L
; Fan S
Proc Natl Acad Sci U S A
2017[Apr]; 114
(17
): 4336-4341
PMID28396436
show ga
We derive four laws relating the absorptivity and emissivity of thermal emitters.
Unlike the original Kirchhoff radiation law derivations, these derivations
include diffraction, and so are valid also for small objects, and can also cover
nonreciprocal objects. The proofs exploit two recent approaches. First, we
express all fields in terms of the mode-converter basis sets of beams; these
sets, which can be uniquely established for any linear optical object, give
orthogonal input beams that are coupled one-by-one to orthogonal output beams.
Second, we consider thought experiments using universal linear optical machines,
which allow us to couple appropriate beams and black bodies. Two of these laws
can be regarded as rigorous extensions of previously known laws: One gives a
modal version of a radiation law for reciprocal objects-the absorptivity of any
input beam equals the emissivity into the "backward" (i.e., phase-conjugated)
version of that beam; another gives the overall equality of the sums of the
emissivities and the absorptivities for any object, including nonreciprocal ones.
The other two laws, valid for reciprocal and nonreciprocal objects, are quite
different from previous relations. One shows universal equivalence of the
absorptivity of each mode-converter input beam and the emissivity into its
corresponding scattered output beam. The other gives unexpected equivalences of
absorptivity and emissivity for broad classes of beams. Additionally, we prove
these orthogonal mode-converter sets of input and output beams are the ones that
maximize absorptivities and emissivities, respectively, giving these beams
surprising additional physical meaning.