Manipulating Light with a Single Layer of Carbon
Researchers have shown that it may be possible to make lasers using single-layer sheets of carbon atoms — the novel material known as graphene. Lasers are made from materials that can absorb ordinary light and then emit photons that have matching waves to provide high intensity. To generate laser power, a material must first undergo a population inversion where an excess of electrons is excited. They must then produce optical gain when one photon is emitted spontaneously causing the excited state electrons to undergo a cascade reaction, each one emitting an additional photon coherent with the first, so a large intensity builds up. Graphene exhibits both of these properties. Very short light pulses, only a few femtoseconds (10-15 seconds) in duration, were used to stimulate the graphene. Almost instantaneously broad population inversions were observed; and the ultrabroad band gain is established at about 10 femtoseconds, producing a much wider tuning range of light (from terahertz to ultraviolet) than in conventional lasing materials. This is remarkable for photonics materials. Comparison of the experiments with newly-developed theoretical approaches neatly explains the findings. This work opens up a wide range of possible uses of graphene in previously-unexplored areas, particularly ultra-fast telecommunications and laser technology. With graphene a little light may go a long way.
- T. Li, L. Luo, M. Hupalo, J. Zhang, M.C. Tringides, J. Schmalian, and J. Wang, Femtosecond Population Inversion and Stimulated Emission of Dense Dirac Fermions in Graphene. Physical Review Letters, 2012, 108, 167401. DOI: 10.1103/PhysRevLett.108.167401