1. Laboratoire EM2C, CNRS, Grande Voie des Vignes, Châtenay-Malabry 92295 Cedex, France
2. CEA CESTA, Le Barp, 33114, France
3. Laboratoire de Microstructures et de Microélectronique, CNRS, av. H. Ravera, 92220 Bagneux, France
4. Present address: The Institute of Optics, University of Rochester, New York 14627, USA

Correspondence to: Jean-Jacques Greffet^1,6 Correspondence and requests for materials should be addressed to J.-J.G. (e-mail: Email: greffet@em2c.ecp.fr).

Abstract

A thermal light-emitting source, such as a black body or the incandescent filament of a light bulb, is often presented as a typical example of an incoherent source and is in marked contrast to a laser. Whereas a laser is highly monochromatic and very directional, a thermal source has a broad spectrum and is usually quasi-isotropic. However, as is the case with many systems, different behaviour can be expected on a microscopic scale. It has been shown recently^{1, 2} that the field emitted by a thermal source made of a polar material is enhanced by more than four orders of magnitude and is partially coherent at a distance of the order of 10 to 100 nm. Here we demonstrate that by introducing a periodic microstructure into such a polar material (SiC) a thermal infrared source can be fabricated that is coherent over large distances (many wavelengths) and radiates in well defined directions. Narrow angular emission lobes similar to antenna lobes are observed and the emission spectra of the source depends on the observation angle—the so-called Wolf effect^{3, 4}. The origin of the coherent emission lies in the diffraction of surface-phonon polaritons by the grating.