Nitzan Livneh

Highly Directional Emission and Photon Beaming from Nanocrystal Quantum Dots Embedded in Metallic Nanoslit Arrays

We demonstrate a directional beaming of photons emitted from nanocrystal quantum dots that are embedded in a subwavelength metallic nanoslit array with a divergence angle of less than 4°. We show that the eigenmodes of the structure result in localized electromagnetic field enhancements at the Bragg cavity resonances, which could be controlled and engineered in both real and momentum space. The photon beaming is achieved using the enhanced resonant coupling of the quantum dots to these Bragg cavity modes, which dominates the emission properties of the quantum dots. We show that the emission probability of a quantum dot into the narrow angular mode is 20 times larger than the emission probability to all other modes. Engineering nanocrystal quantum dots with subwavelength metallic nanostructures is a promising way for a range of new types of active optical devices, where spatial control of the optical properties of nanoemitters is essential, on both the single and many photons level.

Full Spectral and Angular Characterization of Highly Directional Emission from Nanocrystal Quantum Dots Positioned on Circular Plasmonic Lenses

We design a circular plasmonic lens for collimation of light emission from nanocrystal quantum dots at room temperature in the near IR spectral range. We implement a two-dimensional k-space imaging technique to obtain the full spectral-angular response of the surface plasmon resonance modes of the bare plasmonic lens. This method is also used to map the full spectral-angular emission from nanocrystal quantum dots positioned at the center of the circular plasmonic lens. A narrow directional emitting beam with a divergence angle of only ∼4.5° full width at half-maximum is achieved with a spectrally broad bandwidth of 30 nm. The spectrally resolved k-space imaging method allows us to get a direct comparison between the spectral-angular response of the resonant surface plasmon modes of the lens and the emission pattern of the quantum dots. This comparison gives a clear and detailed picture of the direct role of these resonant surface waves in directing the emission. The directional emission effect agrees well with calculations based on the coupled mode method. These results are a step toward fabricating an efficient room-temperature single photon source based on nanocrystal quantum dots.

General closed-form condition for enhanced transmission in subwavelength metallic gratings in both TE and TM polarizations

We present an intuitive reasoning and derivation leading to an approximated, simple closed-form model for predicting and explaining the general emergence of enhanced transmission resonances through rectangular, optically thick metallic gratings in various configurations and polarizations. This model is based on an effective index approximation and it unifies in a simple way the underlying mechanism of enhanced transmission as emerging from standing wave resonances of the different diffraction orders of periodic structures. The model correctly predicts the conditions for the enhanced transmission resonances in various geometrical configurations, for both TE and TM polarizations, and in both the subwavelength and non-subwavelength spectral regimes, using the same underlying mechanism and one simple closed-form equation, and does not require explicitly invoking specific polarization dependent mechanisms. The known excitation of surface plasmons polaritons or slit cavity modes, emerge as limiting cases of a more general condition. This equation can be used to easily design and analyze the optical properties of a wide range of rectangular metallic transmission gratings.

Highly Directional Room-Temperature Single Photon Device

One of the most important challenges in modern quantum optical applications is the demonstration of efficient, scalable, on-chip single photon sources, which can operate at room temperature. In this paper we demonstrate a room-temperature single photon source based on a single colloidal nanocrystal quantum dot positioned inside a circular bulls-eye shaped hybrid metal-dielectric nanoantenna. Experimental results show that 20% of the photons are emitted into a very low numerical aperture (NA < 0.25), a 20-fold improvement over a free-standing quantum dot, and with a probability of more than 70% for a single photon emission. With an NA = 0.65 more than 35% of the single photon emission is collected. The single photon purity is limited only by emission from the metal, an obstacle that can be bypassed with careful design and fabrication. The concept presented here can be extended to many other types of quantum emitters. Such a device paves a promising route for a high purity, high efficiency, on-chip single photon source operating at room temperature.

Simple method for surface selective adsorption of semiconductor nanocrystals with nanometric resolution

Self-assembly methods play a major role in many modern fabrication techniques for various nanotechnology applications. In this paper we demonstrate two alternatives for self-assembled patterning within the nanoscale resolution of optically active semiconductor nanocrystals. The first is substrate selective and uses any high resolution surface patterning to achieve localized self-assembly. The second method uses a surface with poly(methyl methacrylate) (PMMA) resist patterning adsorption of the nanocrystal with covalent bonds and liftoff.

Design, fabrication and characterization of a hybrid metal-dielectric nanoantenna with a single nanocrystal for directional single photon emission

In this work we detail the fabrication method of a hybrid metal-dielectric nanoantenna with a single nanocrystal quantum dot positioned in its center. We have recently shown in [Nano Lett.16, 2527 (2016)] that this device efficiently directs photons from the nanocrystal emission into a small divergence angle perpendicular to the nanoantenna surface. The fabrication method presented here is robust and can be fine-tuned by only a few parameters to achieve high yield of such nanostructures.

Theory and experiments of Bragg cavity modes in passive and active metallic nanoslit array devices

Metallic nanoslit arrays exhibit several unique, surprising, and useful properties, such as resonant enhanced transmission and resonant local field enhancements. Here we present both a theoretical study of these static properties, as well as experiments showing the utilization of these features combined with active optical media. We develop an approximated, simple closed-form model for predicting and explaining the general emergence of enhanced transmission resonances through metallic gratings, in various configurations and polarizations. This model is based on an effective index approximation and it unifies in a simple way the underlying mechanism of all forms of enhanced transmission in such structures as emerging from standing wave resonances of the different diffraction orders of periodic structures. The known excitation of surface plasmon polaritons or slit cavity modes emerges as a limiting case of a more general condition. We also use this understanding of the resonant behavior of nanoslit arrays to design and fabricate such structures with embedded nanocrystal quantum dots, and show beaming of nonclassical light to a narrow angle of less than 4 deg, as well as an enhancement of the two-photon upconversion fluorescence process by a factor of ∼400.

Directional emission of photons from nanocrystal quantum dots using a hybrid plasmonic-dielectric nanoantenna

We design a hybrid circular plasmonic-dielectric nanoantenna for collimation of light emission from nanocrystal quantum dots at room temperature in the near IR spectral range. We implement a two-dimensional k-space imaging technique to obtain the full spectral-angular response of the resonance modes of the hybrid nanoantenna. This method is also used to map the full spectral-angular emission from nanocrystal quantum dots positioned at the center of the hybrid nanoantenna. We achieve a record low 4° divergence angle with a contrast above 17 of the emission into the narrow beam direction compared to emission outside the beam. In addition, we show that the hybrid nanoantenna is operational down to the single quantum dot level and exhibits single photon emission. This is a proof of principal for a room-temperature based single photon source.

Directional Emission of Single Photons From Nanocrystal Quantum Dots Using a Hybrid Plasmonic-Dielectric Nanoantenna

We design a hybrid plasmonic-dielectric nanoantenna for collimation of light emission from nanocrystal quantum dots at room temperature. We show single photon emission with a directional beam with FWHM of less than 3.5 degrees.

Highly Directional Emission of Photons from Nanocrystal Quantum Dots Positioned on Circular Plasmonic Lens Antennas

We show enhanced directional emission from nanocrystal quantum dots positioned at the center of a circular plasmonic lens. A collimation with a divergence of only ~ 4° FWHM is achieved, a spectrally broad bandwidth.