2025/06/10 by Rui Ma, Yang Yu, Ma, R. +7 · 1 citation
Engineering · Physics and Astronomy · #Applied Physics (physics.app-ph) #FOS: Physical sciences #Mechanical and Optical Resonators #Optical properties and cooling technologies in crystalline materials #Optics (physics.optics) #Thermal Radiation and Cooling Technologies
paper · pdf · doi:10.48550/arxiv.2506.08544
openalex publication_date 2025/06/10 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
Thermal radiation is strictly governed by Kirchhoff s law to reach thermal equilibrium. The violation of Kirchhoff s law decouples nonreciprocally the equity between absorptivity and emissivity, enabling exotic thermal engineering applications. However, achieving broadband nonreciprocal thermal emissivity and absorptivity remains a challenge. Here we experimentally demonstrate nonreciprocal and broadband thermal radiation by breaking Kirchhoff s law through nonlinear optical frequency conversion in a scattering medium. Thermal blackbody radiation is upconverted through sum-frequency generation with an intense infrared pump, while broadband conversion is enabled by the critical random quasi-phase-matching condition in the nonlinear nanocrystals. Moreover, a temporal transient measurement also indicates a possible active radiation cooling through such nonlinear thermal radiation. These results may pave a new way for nonlinear and active thermal management in critical applications like radiation cooling, energy harvesting, and infrared camouflage.