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Metalens research has made major advances in recent years. These advances rely on the simple design principle of arranging meta-atoms in regular arrays to create an arbitrary phase and polarization profile. Unfortunately, the concept of equally spaced meta-atoms reaches its limit for high deflection angles where the deflection efficiency decreases. The efficiency can be increased using nano-antennas with multiple elements, but their polarization sensitivity hinders their application in metalenses. Here, it is shown that by designing polarization-insensitive dimer nano-antennas and abandoning the principle of equally spaced unit cells, polarization-insensitive ultrahigh numerical aperture (NA = 1.48) oil-immersion operation with an efficiency of 42% can be demonstrated. This represents a significant improvement on other polarization-insensitive designs at visible wavelength. This single layer metalens is used to replace a conventional objective lens and demonstrates the confocal scanning microscopic imaging of a grating with a period of 300 nm at 532 nm operating wavelength. Overall, the results experimentally demonstrate a novel design concept that further improves metalens performance. [ABSTRACT FROM AUTHOR]

Based on scattering matrix method, we investigate the light emission properties of planar source (i.e., an area current source) in multilayer structures with two-dimensional photonic crystal (PC) patterns. Our numerical results show that the outgoing power from planar source is good agreement with the experimental results of multilayer structures with PC patterns reported before, which clarifies the reason of the big differences between experimental results and theoretical simulations based upon point dipole source. Our studies should provide a deep insight into the underlying physics of quantum optoelectronic devices based upon PC structures. [ABSTRACT FROM AUTHOR]

Surface patterning of p-GaN to improve the light extraction efficiency of GaN-based blue light-emitting diodes (LEDs) has been investigated. Periodic nanopillar arrays on p-GaN have been fabricated by polystyrene (PS) nanosphere lithography; the diameter of the nanopillars can be tuned to optimize the electrical and optical properties of the LEDs. The electroluminescence intensity of the nanopillar-patterned LEDs is better than that of conventional LEDs; the greatest enhancement increased the intensity by a factor of 1.41 at a 20 mA injection current. The enhancements can be explained by a model of bilayer film on a GaN substrate. This method may serve as a practical approach to improve the efficiency of light extraction from LEDs. [ABSTRACT FROM AUTHOR]

We have proposed an easy and controllable method to prepare highly ordered Au nanoarray by pulse alternating current deposition in anodic aluminum oxide template. Using the ultraviolet--visible-near-infrared region spectrophotometer, finite difference time domain, and Green function method, we experimentally and theoretically investigated the surface plasmon resonance, electric field distribution, and local density of states enhancement of the uniform Au nanoarray system. The time-resolved photoluminescence spectra of quantum dots show that the emission rate increased from 0.0429 to 0.5 ns-1 (10.7 times larger) by the existence of the Au nanoarray. Our findings not only suggest a convenient method for ordered nanoarray growth but also prove the utilization of the Au nanoarray for light emission-manipulating antennas, which can help build various functional plasmonic nanodevices. [ABSTRACT FROM AUTHOR]

We investigate the enhancement of the resonance energy transfer rate between donor and acceptor associated by the surface plasmons of the Ag nanorods on a SiO2 substrate. Our results for a single nanorod with different cross sections reveal that the cylinder nanorod has the strongest ability to enhance the resonance energy transfer rate. Moreover, for donor and acceptor with nonparallel polarization directions, we propose simple V-shaped nanorod structures which lead to the remarkable resonance energy transfer enhancement that is ten times larger than that by the single nanorod structure. We demonstrate that these structures have good robustness and controllability. Our work provides a way to improve the resonance energy transfer efficiency in integrated photonic devices. [ABSTRACT FROM AUTHOR]

Using the Green function method, we theoretically achieve good focusing beyond the diffraction limit in a visible light region through a subwavelength slit flanked by grooves. The full width at half maximum (FWHM) of the focused spot reaches 0.3λ (λ is the wavelength of incident light), which is far beyond the diffraction limited line width of 0.5 λ. The phenomena of the exceeding diffraction limit in our structure exist in the range from 500 to 630 nm. Our results can be well explained by the interference interaction between the field of the central slit and the fields penetrating through the grooves. Such image focusing will give rise to various applications in near field microscopy, lithography, high-resolution image and help to improve the design of plasmonic nanodevices. [ABSTRACT FROM AUTHOR]

The quality factor and mode volume of a nanocavity play pivotal roles in realizing the strong coupling interaction between the nanocavity mode and a quantum dot. We present an extremely simple method to obtain the mode volume and investigate the effect of the slab thickness on the quality factor and mode volume of photonic crystal slab nanocavities. We reveal that the mode volume is approximatively proportional to the slab thickness. As compared with the previous structure finely optimized by introducing displacement of the air holes, via tuning the slab thickness, the quality factor can be enhanced by about 22%, and the ratio between the coupling coefficient and the nanocavity decay rate can be enhanced by about 13%. This can remarkably enhance the capability of the photonic crystal slab nanocavity for realizing the strong coupling interaction. The slab thickness tuning approach is feasible and significant for the experimental fabrication of the solid-state nanocavities. [ABSTRACT FROM AUTHOR]

Porous alumina membranes (PAMs) were fabricated using a two-step oxidization method in oxalic acid. Polycrystalline PAMs have been prepared after annealing at different temperatures. The high-temperature properties of the PAMs were investigated using scanning electron microscopy, thermal analysis, X-ray diffraction and infrared spectrometer. At 870°C the amorphous alumina crystallizes to γ-Al2O3. Finally at 1228°C the alumina converts into the thermodynamically preferred phase, α-Al2O3. Differential thermal analysis showed that there was a gradual weight loss at about 900°C due to decomposed of oxalate. A mass of carboxylate ions and carboxylic groups were found in the infrared spectrum of PAMs, and reduced with the increasing of annealing temperature. Characteristic analysis with scanning electron microscopy shows that the pore structure of the PAMs was very stable and there was no detectable structural modification below 900°C, and microstructures of the pores changed slightly during the transformation from α-Al2O3 to γ-Al2O3 while increasing the annealing temperature. [ABSTRACT FROM AUTHOR]

High refractive index TiO2 thin films were deposited on BK7 glass by reactive electron—beam (REB) evaporation at pressure of 2×10−2 Pa, deposition rate of 0.2 nm/s and at various substrate temperatures from 120°C to 300°C. The refractive index and the thickness of the films were measured by visible spectroscopic ellipsometry (SE) and determined from transmission spectra. Optical properties and structure features were characterized by UV-VIS, SEM and XRD, respectively. The measurement and analysis on transmission spectra of all samples show that with the substrate temperature increasing from 120°C to 300°C, the refractive indices of thin films increase from 1.7 to 2.1 and the films after heat treatment have higher refractive indices due to its crystallizing. The XRD analysis results indicate that the structure of TiO2 thin films deposited on BK7 glass at substrate temperatures of 120°C, 200°C and 300°C is amorphous, after post-annealing under air condition at 400°C for 1 hour, the amorphous structure is crystallized, the crystal phase is of 100% anatase with strong preferred orientation (004) and the grain size of crystalline is within 3.6–8.1 nm, which is consistent with results from SEM observation. [ABSTRACT FROM AUTHOR]

In the framework of random-phase approximation theory and applying the self-consistent field method, we study the properties of collective charge density excitations in single quantum well in consideration of dielectric mismatch. We analytically give the general solution of the image potential to the one dimensional Green's function. Our numerical results demonstrate that the dielectric mismatch between the barrier and well materials significantly changes the frequency of the intra- and inter-subband plasmon modes in contrast with dielectric match. We reasonably conclude that the image potential affects the intra- and inter-subband plasmon modes in a different way. [ABSTRACT FROM AUTHOR]

The strong coupling interaction realizes light manipulation at the single-photon level, while the dipole orientation plays a crucial role in the light–matter interaction in anisotropic environments. We investigate the impact of dipole orientation on the strongly-coupled system (SCS) composed of a single quantum dot and a photonic crystal L3 cavity. For both the ideal and the disordered SCS, as the quantum dot deflects from the ideal direction aligning with the cavity mode, the coupling strength and the vacuum Rabi splitting decrease even vanish, the anti-crossing behavior weakens even degrades to crossing behavior, and the vacuum Rabi oscillation period elongates even degrades to the irreversible decay. The dipole orientation has no impact on the coherence time of the SCS. These findings provide significant guidance for the manipulation of the SCS and the characterization of the dipole orientation of the quantum dot. [ABSTRACT FROM AUTHOR]

We demonstrate the utility of optical second harmonic generation (SHG) polarimetry to perform structural characterization of self-assembled zinc-blende/wurtzite III–V nanowire heterostructures. By analyzing four anisotropic SHG polarimetric patterns, we distinguish between wurtzite (WZ), zinc-blende (ZB) and ZB/WZ mixing III–V semiconducting crystal structures in nanowire systems. By neglecting the surface contributions and treating the bulk crystal within the quasi-static approximation, we can well explain the optical SHG polarimetry from the NWs with diameter from 200–600 nm. We show that the optical in-coupling and out-coupling coefficients arising from depolarization field can determine the polarization of the SHG. We also demonstrate micro-photoluminescence of GaAs quantum dots in related ZB and ZB/WZ mixing sections of core–shell NW structure, in agreement with the SHG polarimetry results. The ability to perform in situ SHG-based crystallographic study of semiconducting single and multi-crystalline nanowire heterostructures will be useful in displaying structure-property relationships of nanodevices. [ABSTRACT FROM AUTHOR]