A. Y. Elezzabi

Plasmonically enhanced diffusive and subdiffusive metal nanoparticle-dye random laser

We report on surface plasmon (SP)-enhanced random laser emission from a suspension of silver nanoparticles in a laser dye operating at diffusive and subdiffusive scattering strengths. SP resonance enhances the scattering cross section, while the geometrical cross section remains small, thus providing a large gain volume. The localized electromagnetic field near the particle surface leads to enhanced absorption of excitation light and larger amplification of fluorescence. The metal-nanoparticle-based random laser yields larger linewidth narrowing at lower pump fluence threshold than a dielectric-scatterer-based random laser under equivalent conditions. These findings open the door to studies of applications related to light amplification assisted by SP in metallic nanoparticles.

Experimental realization of subwavelength plasmonic slot waveguides on a silicon platform

We report the experimental realization of horizontal plasmonic slot waveguides capable of subdiffraction modal confinement at IR wavelengths. These waveguides have a propagation length of approximately 6 lambda(g) and are monolithically integrated with conventional silicon photonic waveguides on the same silicon-on-insulator platform. Direct coupling of light from the silicon waveguides to the plasmonic waveguides was achieved with an efficiency of 30% using taper-funnel couplers to obtain mode matching between the two waveguide systems.

Sierpiński fractal plasmonic antenna: a fractal abstraction of the plasmonic bowtie antenna

A new class of bowtie antennas with Sierpiński fractal features is proposed for sensing molecular vibration modes in the near- to mid-infrared. These antennas offer a compact device footprint and an enhanced confinement factor compared to a bowtie antenna. Through extensive simulations, it is shown that these characteristics are related to the ability of this fractal geometry to become polarized. Simulation results demonstrate that these antennas may be tuned between 700 nm ≤ λ ≤ 3.4 µm and that electric field enhancement by 56 is possible at the center of the antenna gap.

Observation of few-cycle, strong-field phenomena in surface plasmon fields

We present experimental evidence of the generation of few-cycle propagating surface plasmon polariton (SPP) wavepackets. Ultrashort plasmonic pulses were generated by few-cycle laser pulses of 5.5 fs to 6.5 fs duration on a thin silver film of 50 nm thickness coated on the face of a right-angle prism to enable Kretschmann-type SPP coupling. SPP pulses were characterized by an autocorrelation-type measurement based on fourth order, nonlinear electron photoemission induced by the SPP field. The evaluation of the measured ultrashort, fringe-resolved autocorrelation curve of the SPP wavepacket (Fig. 1a) resulted in a retrieved SPP pulse length of 6.5 fs, as evidenced by the reconstructed curve in Fig. 1b. This first demonstration of the generation of few-cycle propagating SPP wavepackets on a metal surface has important applications in ultrafast plasmonics.

Laser surgery of zebrafish (Danio rerio) embryos using femtosecond laser pulses: Optimal parameters for exogenous material delivery, and the laser's effect on short- and long-term development

BackgroundFemtosecond (fs) laser pulses have recently received wide interest as an alternative tool for manipulating living biological systems. In various model organisms the excision of cellular components and the intracellular delivery of foreign exogenous materials have been reported. However, the effect of the applied fs laser pulses on cell viability and development has yet to be determined. Using the zebrafish (Danio rerio) as our animal model system, we address both the short- and long-term developmental changes following laser surgery on zebrafish embryonic cells.ResultsAn exogenous fluorescent probe, fluorescein isothiocyanate (FITC), was successfully introduced into blastomere cells and found to diffuse throughout all developing cells. Using the reported manipulation tool, we addressed whether the applied fs laser pulses induced any short- or long-term developmental effects in embryos reared to 2 and 7 days post-fertilization (dpf). Using light microscopy and scanning electron microscopy we compared key developmental features of laser-manipulated and control samples, including the olfactory pit, dorsal, ventral and pectoral fins, notochord, pectoral fin buds, otic capsule, otic vesicle, neuromast patterning, and kinocilia of the olfactory pit rim and cristae of the lateral wall of the ear.ConclusionIn our study, no significant differences in hatching rates and developmental morphologies were observed in laser-manipulated samples relative to controls. This tool represents an effective non-destructive technique for potential medical and biological applications.

Ponderomotive electron acceleration using surface plasmon waves excited with femtosecond laser pulses

We report on the ponderomotive acceleration of electrons using surface plasmon (SP) waves launched on Ag and Au films. High-energy electrons, up to 2 keV, are generated in the high spatial gradient of the SP field. Acceleration gradients of ∼8GeV∕m are produced using 30GW∕cm2, 800 nm amplified 30 fs laser pulses. Investigation of the photoemission characteristics of these metal films reveals a distinct transition between the multiphoton regime and a laser-induced field emission regime. Results of the experiment are in good agreement with those predicted with test particle code, which is based on finite-difference time-domain simulation and incorporates the Drude dielectric function and photoemission properties of the metallic films.

Two-photon photoconductive terahertz generation in ZnSe

We report on the generation of free-space terahertz (THz) radiation using polycrystalline ZnSe as the photoconductive (PC) substrate. It is found that the ZnSe emitter can be operated at peak fields up to 125 kV/cm without dielectric breakdown, and can be photoexcited (through two-photon absorption) at pump energy fluences up to 28 mJ/cm2 without saturating. The relationship between the THz field strength and the excitation conditions of the PC gap are interpreted through a photocarrier transport model.

Strong-field plasmonic electron acceleration with few-cycle, phase-stabilized laser pulses

We carried out experimental investigations on surface plasmon enhanced electron acceleration with few-cycle, carrier-envelope phase (CEP) stabilized laser pulses. We determined the spectrum of electrons accelerated in the plasmonic field and found that signatures of the phase stabilized optical waveform driving the individual electron trajectories are washed out in the electron spectra. We attribute this effect to nanoscale surface roughness of the metallic samples, as supported by extensive numerical simulations. This finding explains the previously observed, low CEP sensitivity of photoemission processes from metallic films and enables the development of femtosecond electron sources for ultrafast time-resolved applications.

Nanoscale plasmonic contour bowtie antenna operating in the mid-infrared.

A plasmonic antenna design is proposed and investigated numerically over a large parameter space. By considering the contour of a bowtie antenna and introducing an additional design parameter, the contour thickness, it is demonstrated that the resonant wavelength of the antenna may be tuned over a broad spectral range while maintaining a constant antenna footprint. These new antennas allow for a factor of 3.6 reduction in the antenna footprint and an increase in the gap enhancement by 28%.

Monolithic integration of plasmonic waveguides into a complimentary metal-oxide-semiconductor- and photonic-compatible platform

A silicon-based plasmonic waveguide was designed and fabricated for use at telecommunications wavelengths. This waveguide is interfaced to the silicon photonics platform by use of a tapered silicon-on-insulator waveguide. Simulations indicate that this scheme excites the transverse magnetic plasmonic mode and that the electric fields are confined to the silicon-gold interface. Transmitted power is measured for several device lengths and the propagation distance and coupling efficiency are found to be 2.00 μm and 38.0%, respectively. These results demonstrate the potential for integration between silicon photonics and silicon plasmonic devices and demonstrate the ability to incorporate silicon-based plasmonic devices into complimentary metal-oxide-semiconductor electronic and photonic circuitry.