THz thermal radiation enhancement using an electromagnetic crystal

Thermal radiation in the terahertz (THz) range only occupies a tiny portion of the whole blackbody power spectrum at room temperature. We demonstrate that a thermal radiator, which is constructed from an electromagnetic (EM) crystal, can be designed so that its photon density of states (DOS) is enhanced in the THz frequency range. We also demonstrate, as a consequence, that this source may lead to large enhancements of the radiated power over the values associated with normal blackbody radiation at those frequencies. The THz thermal radiation enhancement effects of various EM crystals, including both silicon and tungsten woodpile structures and a cubic photonic cavity (CPC) array, are explored. The DOS of the woodpile structures and the CPC array are calculated, and their thermal radiation intensities are predicted numerically. These simulations show that the radiated power can be enhanced by a factor of 11.8 around 364 GHz and 2.6 around 406 GHz, respectively, for the silicon and tungsten woodpile structures in comparison to the normal blackbody radiation values at those frequencies. It is also shown that an enhancement factor of more than 100 may be obtained by using the CPC array. A silicon woodpile EM crystal with a band gap around 200 GHz was designed and fabricated. The transmission property of this woodpile structure was verified using the THz time-domain spectroscopy (TDS). Thermal emissions from the fabricated silicon woodpile and a control blackbody sample were measured. Enhancements of the woodpile source radiation over the blackbody were observed at several frequencies which are consistent with the theoretical predictions.