Universal modal radiation laws for all thermal emitters

Area of Science:

• Optics and Photonics
• Thermodynamics
• Electromagnetism

Background:

• Kirchhoff's radiation law traditionally describes thermal emission and absorption for macroscopic, reciprocal objects.
• Existing derivations do not account for diffraction effects, limiting their applicability to small objects.
• Nonreciprocal materials, which violate the principle of reciprocity, present unique challenges for radiation laws.

Purpose of the Study:

• To derive new laws governing the absorptivity and emissivity of thermal emitters.
• To extend the validity of radiation laws to include diffraction effects, small objects, and nonreciprocal materials.
• To provide a more comprehensive theoretical framework for understanding thermal radiation.

Main Methods:

• Utilizing mode-converter basis sets of beams to express optical fields.
• Employing thought experiments with universal linear optical machines and black bodies.
• Developing proofs that incorporate diffraction and consider nonreciprocal objects.

Main Results:

• Derived four novel laws relating absorptivity and emissivity.
• Two laws rigorously extend known principles for reciprocal objects and generalize to nonreciprocal ones.
• Two additional laws reveal unexpected equivalences for broad classes of beams, valid for both reciprocal and nonreciprocal objects.
• Demonstrated that specific orthogonal beam sets maximize absorptivity and emissivity.

Conclusions:

• The derived laws offer a generalized understanding of thermal radiation, applicable beyond classical limitations.
• These findings have implications for designing advanced thermal emitters and understanding radiative properties of nanoscale and exotic materials.
• The identified optimal beam sets provide new physical meaning and potential applications in optical engineering.