We report on the first experimental demonstration of a new type of electron-beamdriven radiation source, a 'light-well', which can be used as a tunable nanoscale emitter of optical radiation and surface plasmon-polaritons (SPPs)

Adamo, Giorgio

Fu, Yuan Hsing

García de Abajo, F.Javier

MacDonald, Kevin F.

Tsai, Din Ping

Wang, Chih-Ming

Zheludev, Nikolay I.

English

Southampton (e-Prints Soton)

 Free-electron pumped tunable nanoscale light-source: the “light-well”  Giorgi o Adamo1, Yuan Hsing Fu2, Kevin F. MacDonald1, Chi h-Ming Wang2, Din Ping Tsai2,  F.  Javier García de Abajo3 and Nikolay I. Zheludev1 1Optoelectronic s Research Centre, University o f Southampton, Southampton, SO17 1BJ, UK 2Department of Physics, National Taiwan University, Taipei 10617, Taiwan, Republic of China 3Instituto de Optica, CSIC, 28006 Madrid, Spain  Purpose We report on the first experimental demonstration of a new type of electron-beam-driven radiation source, a ‘light-well’, which can be used as a tunable nanoscale emitter of optical radiation and surface plasmon-polaritons (SPPs).    Methods In  a  free-electron laser (FEL) a beam of electrons  emit s light as it passes through an ‘undulator’  – a region of alternating magnetic fields. Similarly, in the light-well a beam of free-electron  generates optical photons and SPPs via exposure to a periodic dielectric environm ent as it  passes through a cylindrical nano-hole in a layered metal -dielectric structure . The emission wavelength can be tuned by changing the electron  energy.  The source has an optical output power of the order of 0.1 nW which corresponds to an emission intensity of ~200 W/cm2.  Experimental light-well nano-holes were milled, using a focused ion beam, through a multilayer stack of alternating  200 nm gold and silica layers sputtered onto a silicon substrate (Fig. 1).  Experimental measurements of light-well optical emission were performed using the hyperspectral imaging mode  [1]  of a scanning electron microscope equipped with a spectrograph and nitrogen-cooled CCD array for detection and analysis of emitted light. Results When an elect ron beam is injected into a light-well nano-hole, the emission spectrum is found to contain two peaks (Fig. 2a) with  spectral positio ns  that  depend on the electron acceleration voltage (Fig. 2b). The total emission intensity is found to increase with beam current and as the injection point approaches the wall of the light-well, and to decrease with the well diameter.  Light-well  output results from a combination of material - and geometry-dependent electron -beam-induced emission processes,  including  Smith-Purcell radiation  [2]  and  SPP  excitation on the numerous metal-dielectric interfaces within the structure.  In analyzing light-well emission characteristics, we consider the electromagnetic modes supported by periodically structured nano-caviti es  (Fig 2b) and numerically model light-well structures using the boundary element method [3]. Conclusions With dimen sions of  a few hundred nanometers and a structure compatible with silicon -based technologies,  the light-well  may be employed in highly -integrated nanophotoni c circuits as chip-scale free-electron radiation sources, or in densely packed ensembles for optical memory or  ‘surface -conduction electron-emitter’  and field -emission d isplay  applications.  References [1]  M. V.  Bashevoy et al.,  Opt. Exp.  15, 11313 (2007) [2]  S. J.  Smith  & E.  M. Purcell , Phys.  Rev. 92, 1069 (1953)  [3]  F. J. García d e Abajo & A. Howie, P hys. Rev. B  65, 115418 (2002) Figure 1: (a) Schematic section of a light-well. (b) Secondary electron images of the gold -silica multilayer and of a light-well  (c). (a)  (b)  (c) 72077082087017 23 29 35 41Electron energy, keVPeak position, nm0100200300400700 800 900Wavelength, nmEmission intensity, arb. units (a)  1 2theory experiment  (b)  Figure 2: (a) Emission spectrum of a 700 nm diameter light-well for 40 keV electrons injected at a point ~100 nm inside the wall of the well. (b) Spectral position of peak 1 in experiments (blue) and theory (red). 

García d e Abajo

Free-electron pumped tunable nanoscale light-source: the 'light-well'

Free-electron pumped tunable nanoscale light-source: the 'light-well'

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