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Ultrafast switching of tunable infrared plasmons in indium tin oxide nanorod arrays with large absolute amplitude


All-optical control of plasmons can enable optical switches with high speeds, small footprints and high on/off ratios. Here we demonstrate ultrafast plasmon modulation in the near-infrared (NIR) to mid-infrared (MIR) range by intraband pumping of indium tin oxide nanorod arrays (ITO-NRAs). We observe redshifts of localized surface plasmon resonances arising from a change of the plasma frequency of ITO, which is governed by the conduction band non-parabolicity. We generalize the plasma frequency for non-parabolic bands, quantitatively model the fluence-dependent plasma frequency shifts, and show that different from noble metals, the lower electron density in ITO enables a remarkable change of electron distributions, yielding a significant plasma frequency modulation and concomitant large transient bleaches and induced absorptions, which can be tuned spectrally by tailoring the ITO-NRA geometry. The low electron heat capacity explains the sub-picosecond kinetics that is much faster than noble metals. Our work demonstrates a new scheme to control infrared plasmons for optical switching, telecommunications and sensing.

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Figure 1: Static optical characterization and simulation of plasmonic ITO-NRA in the infrared.
Figure 2: Transient absorption measurements of the ITO-NRA in both the NIR and MIR.
Figure 3: Non-parabolic band-induced plasma frequency modulation.
Figure 4: Tunability of the MIR transient response through changing incidence angles and ITO-NRA geometries.


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The work was funded by the MRSEC program (NSF DMR-1121262) at Northwestern University. Use of the Center for Nanoscale Materials was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. This work made use of the EPIC facility (NUANCE Center-Northwestern University), which has received support from the MRSEC program (NSF DMR-1121262) at the Materials Research Center; the International Institute for Nanotechnology (IIN); and the State of Illinois, through the IIN. The work also used the Northwestern University Micro/Nano Fabrication Facility (NUFAB), which is supported by the State of Illinois and Northwestern University.

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P.G., R.D.S. and R.P.H.C. designed experiments. P.G. fabricated the sample, performed static measurements and conceived the non-parabolicity mediated plasma frequency. R.D.S. performed transient absorption experiments. J.B.K. and P.G. developed the theory for the plasma frequency in nonparabolic bands. P.G. analysed experimental data, performed numerical computations and wrote the manuscript. R.P.H.C. supervised the project. All authors discussed the results and contributed to writing and editing of the manuscript.

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Correspondence to Robert P. H. Chang.

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The authors declare no competing financial interests.

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Guo, P., Schaller, R., Ketterson, J. et al. Ultrafast switching of tunable infrared plasmons in indium tin oxide nanorod arrays with large absolute amplitude. Nature Photon 10, 267–273 (2016).

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