Paper NS+NC-WeA8
Coherence and Polarization Properties of Thermal Radiation Emitted by Metallic Nanowires

Wednesday, October 22, 2008, 4:00 pm, Room 311

We investigate the coherence properties of the thermal radiation emitted from resistively heated individual metallic nanowires. High aspect ratio nanowires are fabricated by e-beam lithography with widths from 60 nm up to 2 µm, dimensions well below the wavelength of the emitted thermal radiation. The coherence of thermal radiation is probed by self interfering the radiation from the nanowire with its image in a movable mirror. As the mirror approaches the nanowire, well defined interference fringes are observed. From the fringe visibility we extract the coherence length of the emitted thermal radiation. For nanowire width above 2 um the coherence length of the thermal radiation emitted by nanowires is similar to blackbody radiator. As the nanowire gets narrower an increased fringe visibility and higher coherence length is measured. A lower bound for the coherence length for thermal radiation is estimated to be 30 µm for very narrow metal nanowires well above 4 µm for the blackbody radiation.Furthermore the coherence length is increasing as the temperature of the nanowire is decreased. For very narrow nanowires the thermal radiation is polarized with very high extinction ratio. Either changing the width of the nanowire or the nanowire temperature the polarization can be rotated from a longitudinal to a tranversal direction to the long axis of the nanowire. Both the increased coherence and polarization of the thermal radiation can be related to correlation of the charge fluctuation and charge confinement in narrow structures. We discuss various approaches to further increase the coherence of the thermal radiation emitted by nanowires and their applications as sub-wavelength coherent infrared light sources.