Plasmonic quantum cascade laser antenna

We report a plasmonic quantum cascade laser antenna that confines coherent midinfrared radiation well below the diffraction limit. The antenna was fabricated on the facet of a midinfrared quantum cascade laser and consists of a pair of gold nanorods separated by a gap. The antenna near field was characterized by an apertureless near-field scanning optical microscope; field confinement of about 100 and 70 nm, limited by the gap size, was demonstrated at wavelengths of 7.0 and 5.3 mu m, respectively. This device may find important applications in midinfrared subwavelength chemical and biological imaging and spectroscopy. (C) 2007 American Institute of Physics.