Polarization Engineering of Thermal Radiation Using Metallic Photonic Crystals

Thermal radiation (TR) from a hot object was one of the clues that led to the development of quantum physics a century ago. Recently it has attracted renewed scientific interest as extraordinary phenomena have been demonstrated for objects patterned periodically on the micrometer scale, for example, coherent TR and spectrally enhanced TR. While TR has been known to be polarized by fundamental optical phenomena, such as refraction and diffraction, engineering the polarization of TR has been attempted by few. Polarization-engineered thermal emitters have the potential to enable higher conversion efficiency in thermophotovoltaics. Herewe report that a series of polarized thermal emitters (PTEs) can be selectively enhanced with a high degree of polarization (DOP) up to 0.5 through the use of metallic photonic crystals (MPCs). We show that strong absorption induced by greatly reduced group velocity for a certain polarization is the underlying physical basis for this phenomenon. As the PTEs have two TR channels with different linear polarizations, advanced applications such as tunable multichannel infrared (IR) emitters and encrypted infraredmarkers are also possible. Recently we reported that a nickelMPCwith only two layers (as in Fig. 1a) has two highly enhanced TR peaks when a homogeneous backplane is added. For this study, we have fabricated twomore variations having mutual angles of 608 and 308, as seen in Figure 1b and c to study polarized TR. We designate the MPCs as 908, 608, and 308 MPCs, respectively. Measurements were made using the radiometric setup shown