Thermal photonics and applications
Materials in thermal equilibrium contain charges in random motion that generate fluctuating currents, and these currents, in turn, radiate electromagnetic fields. The charges can be electrons in metals or ions in polar materials. Although in neutral materials the random density charges, currents, and the generated electromagnetic fields vanish in average, the energy radiated by these thermal fields is not zero and constitutes a radiative mechanism for heat transport between object out of contact. Moreover, the radiative heat transfer between bodies separated by a large distance is bounded by the blackbody limit. In this limit, corresponding to the far-field regime, the power radiated by the bodies is given by the Stefan-Boltzmann law. However, when the separation distance is reduced below the characteristic thermal wavelength of the radiation, that is, in the near-field regime, the radiative heat transfer is considerably enhanced as compared to the blackbody limit. In the near field, the main mechanism for radiative heat transfer is due to photon tunneling through evanescent states of the electromagnetic field. Interestingly, the thermal wavelength defining near-field scales is about 8 microns at room temperature and structures with interactions in the near field are nowadays achievable with several fabrication techniques. Near-field radiative effects are relevant in many physical situations, for instance, in the generation of usable energy from thermal sources, radiative cooling devices and in devices for nanoscale thermal management. Next we describe some selected results of our research in this field.