Compressing surface plasmons for nano-scale optical focusing

Abstract

A major challenge in optics is how to deliver and concentrate light from the micron-scale into the nano-scale. Light can not be guided, by conventional mechanisms, with optical beam sizes significantly smaller than its wavelength due to the diffraction limit. On the other hand, focusing of light into very small volumes beyond the diffraction limit can be achieved by exploiting the wavelength scalability of surface plasmon polaritons. By slowing down an optical wave and shrinking its wavelength during its propagation, optical energy can be compressed and concentrated down to nanometer scale, namely, nanofocusing. Here, we experimentally demonstrate and quantitatively measure the nanofocusing of surface plasmon polaritons in tapered metallic V-grooves down to the deep subwavelength scale - approximately lambda/40 at wavelength of 1.5 micron - with almost 50% power efficiency.

Plasmonic generation of ultrashort extreme-ultraviolet light pulses

“…The NIR pulses were focused via an aspheric lens to a 5-mmdiameter spot on the inlet aperture, which had elliptical major-and minor-axis diameters of 4.4 mm and 2.2 mm, respectively. The focused spot yielded an intensity of 5 × 10 11 W cm 22 , which was two orders of magnitude lower than the threshold intensity required for high-harmonic generation. The entire sub-assembly of the waveguide was contained in a gas cell with dimensions of 11 mm × 11 mm × 3 mm, inside which xenon gaseous atoms were supplied with a controlled pressure of 70 torr.…”

“…The plasmonic wave maintains the fundamental anti-symmetric mode of propagation inside the waveguide, and cannot therefore escape through the small exit aperture. Consequently, the plasmonic wave reverses its propagation direction at the point where the minor-axis diameter of the tapered waveguide reduces to below half its wavelength [22][23][24] . This cutoff effect gives rise to a counter-propagating wave that subsequently interferes with the incoming wave.…”

“…The waveguide is a metallic nanostructure made of silver and has a hollow hole that takes the shape of a tapered cone with its elliptical cross-section decreasing from the inlet aperture (minor-axis diameter, 2 mm) to the exit aperture (minor-axis diameter, 100 nm). The incident NIR pulses are focused on the inlet aperture at a repetition rate of 75 MHz with a moderate intensity of 1 × 10 11 W cm 22 . While each NIR pulse propagates through the tapered hole towards the exit aperture, the electric field intensity inside the hole undergoes a substantial boost that is sustained by the SPPs driven by the incident NIR pulse.…”

Exciton-plasmon coupling interactions: from principle to applications

“…If F g < 1, the spontaneous emission rate is inhibited; otherwise, the cavity enhances the emission. This formula of Equation (29) shows that the optical resonator can significantly increase the emission rate while compressing the light to a small range and storing it for a long time [155,156]. However, the realization of these two goals in the strict sense is contradictory, because the tighter confinement is always accompanied by high losses.…”

Ultraslow waves on the nanoscale

“…We note that under similar conditions non-coherent multi-photon or high-field fluorescence may also dominate the spectra (74), since these effects too are favored below the ionization threshold by the large field-enhancements and the linear interaction length scaling. This type of broadband slow-light structures need not be planar (38,(65)(66)(67) nor linearly tapered (40)(41)(42)(73)(74)(75)(76)(77)(78)(79)(80)(81)(82), with two examples being the cylindrically (64) or spherically (83) crescent nanostructures ( Fig. 1E and Fig.…”