Quantum mechanics

Reflection (computer programming)

Engineering

Spacetime

Emissivity

Materials science

Radiation

Infrared

Modulation (music)

Computer science

Acoustics

Chemical engineering

Wavelength

Thermodynamics

Physics

Optics

Thermal

Grating

Molar absorptivity

Space time

Programming language

Thermal radiation

Meteorology

Angle of incidence (optics)

ACS Photonics

We present an infrared thermal emitter that exhibits unequal emissivity and absorptivity for a given frequency and angle of incidence, violating Kirchhoff's law of thermal radiation. We exploit spatio-temporal modulation of the refractive index of a grating to drive photonic transitions between guided resonance modes. We show via simulations that the modulation results in directional-dependent reflection. Using a generalized law of thermal radiation valid in the presence of mode conversion, we directly calculate absorptivity and emissivity for our structures. We show that a strong contrast between absorptivity and emissivity can be obtained close to a wavelength of 3.6 μm for realistic modulation frequencies of 10s of GHz. Furthermore, we show that for strong modulation, the system exhibits directional Rabi splitting, giving rise to a stronger contrast between emissivity and absorptivity. The results thus predict the feasibility of nonreciprocal infrared thermal emission without the use of magneto-optical materials.

Violation of Kirchhoff’s Law of Thermal Radiation with Space–Time Modulated Grating