Theory of Thermal Emissivity and Enhanced Absorption in Sub-wavelength Metallo-Dielectric Photonic Crystals
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1014-AA11-05
Theory of Thermal Emissivity and Enhanced Absorption in Sub-Wavelength MetalloDielectric Photonic Crystals Rana Biswas1, Irina Puscasu2, Martin Pralle2, Martin McNeal2, Anton Greenwald2, James Daly2, Edward Johnson2, Srinivas Neginhal3, and Changgeng Ding4 1 Dept of Physics, Microelectronics Res Ctr, Ames Laboratory, Iowa State University, Dept of Electrical & Computer Engineering, Ames, IA, 50011 2 Ion Optics, 411 Waverly Oaks Road, Waltham, MA, 02452 3 Dept. of Electrical and Computer Engineering, Iowa State University, Ames, IA, 50011 4 Dept of Physics and Microelectronics Research Center, Iowa State University, Ames, IA, 50011 ABSTRACT Metallo-dielectric photonic crystals are sharp thermal emitters at infrared wavelengths, and are being employed in sensors. We describe the theory of thermal emission and enhanced absorption in these photonic crystals using a scattering matrix approach, where Maxwell’s equations are solved in Fourier space. A sub-wavelength hole array in a metal layer is coupled to a twodimensional photonic crystal of the same periodicity in these metallo-dielectric photonic crystals. The sub-wavelength hole array has an enhanced transmission mode that couples to a weakly guided mode of the photonic crystal having similar modal character. The transmissive mode of the hole array is absorbed by the photonic crystal to create a sharp absorption and reflective minimum. The enhanced absorption is investigated in different lattice symmetries.
INTRODUCTION A novel spectroscopic gas sensor has been fabricated by Ion-Optics [1-4] for infrared sensing applications, and detection of gaseous species. The underlying principle of this sensor is that gases have characteristic absorption lines in the infrared. The Ion-Optics device uses a metallo-dielectric photonic crystal that thermally emits radiation in a narrow band of wavelengths in the infrared regime when heated [1-6]. As described by Puscasu et al [1], the emissive device acts as its own sensor, thereby measuring the absorption of the gas at the desired wavelength region. When there is absorbing gas in the chamber less reflected power is collected and the device equilibrates at a lower temperature. The difference of temperature (∆T) causes a change in resistance of the metal, and a change in voltage across the metal resistance. The change in voltage is proportional to the gas concentration in the chamber, and has been carefully calibrated to the gas concentration in experimental studies. This miniaturized spectroscopic sensor has many advantages over conventional sensors with growing commercial potential. Here we simulate the structure to understand the complex underlying physics of emission and absorption. The device developed by Ion-Optics consists of a sub-wavelength array of holes in a thin metal sheet that resides on a two-dimensional silicon photonic crystal. By controlling the lattice spacing of the holes, the emissive wavelength can be controlled.
BACKGROUND The discovery of extraordinary transmission in a hole array by Ebbesen e
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