Ultrafast ZnO nanowire lasers: nanoplasmonic acceleration of gain dynamics at the surface plasmon polariton frequency
Themistoklis P. H. Sidiropoulos, Sebastian Geburt, Robert Röder, Ortwin Hess, Stefan A. Maier, Carsten Ronning, Rupert F. Oulton
2014
CLEO: 2014
unpublished
Light-matter interactions are inherently slow as the wavelengths of optical and electronic states differ greatly. Surface plasmon polaritons, electromagnetic excitations at metal-dielectric interfaces, have generated significant interest because their spatial scale is decoupled from the vacuum wavelength, promising accelerated light-matter interactions. Meanwhile, the possibility of accelerated dynamics in recently demonstrated surface plasmon lasers remains to be verified. In this letter, we
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... port the observation of <800 fs pulses from hybrid plasmonic zinc oxide (ZnO) nanowire lasers. Operating at room temperature, ZnO excitons lie near the SPP frequency in such silver-based plasmonic lasers, leading to accelerated spontaneous recombination, gain switching, and gain recovery compared to conventional ZnO nanowire lasers. Surprisingly the laser dyanmics can be as fast as gain thermalization in ZnO, which precludes lasing in the thinnest nanowires (diameter < 120 nm). The capability to combine surface plasmon localization with ultrafast amplification provides the means for generating extremely intense optical fields with applications in sensing, non-linear optical switching, as well as in the physics of strong field phenomena. Lasers that use metallic cavities have emerged recently as a new class of light source 1-3 . Plasmonic lasers achieve optical confinement and feedback using surface plasmon polaritons (SPPs), quasiparticles of photons and electrons at metal-dielectric interfaces, which can be amplified by suitable optical gain media 4 . The high gain of inorganic crystalline semiconductors is typically necessary to overcome fast electron scattering in metals (~10 fs), which leaves plasmonic lasers with high parasitic cavity loss. Nevertheless, SPPs offer the capability to reduce optical mode sizes far below the scale of the vacuum wavelength 3,5-8 leading to compact lasers that can generate extremely focussed optical excitations on potentially ultrafast time scales 1,9 with applications in Raman sensing 10-12 , non-linear frequency generation 13-15 , and non-linear optical switching 16 . Despite the draw-back of loss, numerous plasmonic lasers have been reported recently with progress being made towards reducing the laser threshold to a point where practical applications are viable. In particular, several devices now operate at room temperature 7,17 and even under electrical injection 18 . While the practical issues of these devices have seen progress, few experimental works have studied their underlying limitations and capabilities. In terms of limitations, it is currently unclear how much confinement is realistically sustainable. In plasmonics confinement is associated
doi:10.1364/cleo_qels.2014.fth3k.5
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