A femtosecond-laser nanostructuring technique that blackens metal has been applied by its inventors to tungsten lamp filaments, enhancing their emission efficiency to near 100%. In practical terms, this means that a treated 60 W incandescent bulb could produce as much light as a 100 W untreated version. Researchers at the University of Rochester (Rochester, NY) and the Research Institute for Complex Testing of Optoelectronic Devices (City of Sosnovy Bor, Russia) treat a ribbon filament with 65 fs pulses at an 800 nm wavelength and a 1 kHz repetition rate to create a surface structure that is a combination of random-appearing fused nanostructures with a ribbed microstructure having a period of 0.48 µm.
Nanostructures on metal can couple thermally excited surface plasmons to free-space radiation. The light enhancement of the treated lamp was highest at 800 nm, less significant at 630 nm, and least at 400 nm. The researchers discovered that the emitted light was partially polarized, an effect produced by the ribbed structure. They believe that optimizing the processing conditions (currently, they optimize the blackness simply by visual examination) will allow them to further improve the emission efficiency. Contact Anatoliy Vorobyev at [email protected].