Haoliang Qian

Giant Kerr response of ultrathin gold films from quantum size effect.

With the size of plasmonic devices entering into the nanoscale region, the impact of quantum physics needs to be considered. In the past, the quantum size effect on linear material properties has been studied extensively. However, the nonlinear aspects have not been explored much so far. On the other hand, much effort has been put into the field of integrated nonlinear optics and a medium with large nonlinearity is desirable. Here we study the optical nonlinear properties of a nanometre scale gold quantum well by using the z-scan method and nonlinear spectrum broadening technique. The quantum size effect results in a giant optical Kerr susceptibility, which is four orders of magnitude higher than the intrinsic value of bulk gold and several orders larger than traditional nonlinear media. Such high nonlinearity enables efficient nonlinear interaction within a microscopic footprint, making quantum metallic films a promising candidate for integrated nonlinear optical applications.

Broadband Photonic Spin Hall Meta-Lens

Meta-lens represents a promising solution for optical communications and information processing owing to its miniaturization capability and desirable optical properties. Here, spin Hall meta-lens is demonstrated to manipulate photonic spin-dependent splitting induced by spin-orbital interaction in transverse and longitudinal directions simultaneously at visible wavelengths, with low dispersion and more than 90% diffraction efficiency. The broadband dielectric spin Hall meta-lens is achieved by integrating two geometric phase lenses with different functionalities into one single dynamic phase lens, which manifests the ultracompact, portable, and polarization-dependent features. The broadband spin Hall meta-lens may find important applications in imaging, sensing, and multifunctional spin photonics devices.

Quantum Electrostatic Model for Optical Properties of Nanoscale Gold Films

Abstract The optical properties of thin gold films with thickness varying from 2.5 nm to 30 nm are investigated. Due to the quantum size effect, the optical constants of the thin gold film deviate from the Drude model for bulk material as film thickness decreases, especially around 2.5 nm, where the electron energy level becomes discrete. A theory based on the self-consistent solution of the Schrödinger equation and the Poisson equation is proposed and its predictions agree well with experimental results.

Nanostructuring Multilayer Hyperbolic Metamaterials for Ultrafast and Bright Green InGaN Quantum Wells

Semiconductor quantum well (QW) light-emitting diodes (LEDs) have limited temporal modulation bandwidth of a few hundred MHz due to the long carrier recombination lifetime. Material doping and structure engineering typically leads to incremental change in the carrier recombination rate, whereas the plasmonic-based Purcell effect enables dramatic improvement for modulation frequency beyond the GHz limit. By stacking Ag-Si multilayers, the resulting hyperbolic metamaterials (HMMs) have shown tunability in the plasmonic density of states for enhancing light emission at various wavelengths. Here, nanopatterned Ag-Si multilayer HMMs are utilized for enhancing spontaneous carrier recombination rates in InGaN/GaN QWs. An enhancement of close to 160-fold is achieved in the spontaneous recombination rate across a broadband of working wavelengths accompanied by over tenfold enhancement in the QW peak emission intensity, thanks to the outcoupling of dominating HMM modes. The integration of nanopatterned HMMs with InGaN QWs will lead to ultrafast and bright QW LEDs with a 3 dB modulation bandwidth beyond 100 GHz for applications in high-speed optoelectronic devices, optical wireless communications, and light-fidelity networks.

Controlled Homoepitaxial Growth of Hybrid Perovskites

Organic-inorganic hybrid perovskites have demonstrated tremendous potential for the next-generation electronic and optoelectronic devices due to their remarkable carrier dynamics. Current studies are focusing on polycrystals, since controlled growth of device compatible single crystals is extremely challenging. Here, the first chemical epitaxial growth of single crystal CH3 NH3 PbBr3 with controlled locations, morphologies, and orientations, using combined strategies of advanced microfabrication, homoepitaxy, and low temperature solution method is reported. The growth is found to follow a layer-by-layer model. A light emitting diode array, with each CH3 NH3 PbBr3 crystal as a single pixel, with enhanced quantum efficiencies than its polycrystalline counterparts is demonstrated.

Second-harmonic susceptibility enhancement in Gallium nitride nanopillars

Second-harmonic generation (SHG) from single GaN nanpoillar is reported. A model for the SHG processes in the GaN nanopillar as a function of diameter is presented; the analysis showed quantitatively that the SHG is dominated by its surface area. The effective second order nonlinear optical susceptibility increases as the diameter of the GaN nanopillar decreases, reaching a value of 136 pm/V at 150nm diameter, making them attractive for modulator applications.

Three-dimensional fluorescent microscopy via simultaneous illumination and detection at multiple planes

The conventional optical microscope is an inherently two-dimensional (2D) imaging tool. The objective lens, eyepiece and image sensor are all designed to capture light emitted from a 2D ‘object plane’. Existing technologies, such as confocal or light sheet fluorescence microscopy have to utilize mechanical scanning, a time-multiplexing process, to capture a 3D image. In this paper, we present a 3D optical microscopy method based upon simultaneously illuminating and detecting multiple focal planes. This is implemented by adding two diffractive optical elements to modify the illumination and detection optics. We demonstrate that the image quality of this technique is comparable to conventional light sheet fluorescent microscopy with the advantage of the simultaneous imaging of multiple axial planes and reduced number of scans required to image the whole sample volume.

Experimental Demonstration of Hyperbolic Metamaterial Assisted Illumination Nanoscopy

An optical metamaterial is capable of manipulating light in nanometer scale that goes beyond what is possible with conventional materials. Taking advantage of this special property, metamaterial-assisted illumination nanoscopy (MAIN) possesses tremendous potential to extend the resolution far beyond conventional structured illumination microscopy. Among the available MAIN designs, hyperstructured illumination that utilizes strong dispersion of a hyperbolic metamaterial (HMM) is one of the most promising and practical approaches, but it is only theoretically studied. In this paper, we experimentally demonstrate the concept of hyperstructured illumination. A ∼80 nm resolution has been achieved in a well-known Ag/SiO2 multilayer HMM system by using a low numerical aperture objective (NA = 0.5), representing a 6-fold resolution enhancement of the diffraction limit. The resolution can be significantly improved by further material optimization.

Light emission enhancement by using patterned multilayer hyperbolic metamaterials

We study nanopatterned multilayer hyperbolic metamaterials with tunable plasmonic properties for enhancing fluorescent molecules and LEDs at different working wavelengths. About two order of magnitude of spontaneous emission rate enhancement was demonstrated.

Investigation of the reflection and transmission of nano-scale gold films

The reflection and transmission of thin gold films with thickness varying from 2.5 nm to 30 nm are experimentally investigated. A theory is proposed and explains all experimental data.