Coherent and tunable nanoscale light sources utilizing optical nonlinearities are required for applications ranging from imaging and bio-sensing to on-chip all-optical signal processing. However, owing to their small sizes, the efficiency of nanostructures even with high nonlinear coefficients is poor, therefore requiring very high excitation energies. Although surface-plasmon resonances of metal nanostructures can enhance surface nonlinear processes such as second-harmonic generation, they still suffer from low conversion efficiencies owing to their intrinsically low nonlinear coefficients. Here we show highly enhanced and directional second-harmonic generation from individual CdS nanowires integrated with silver nanocavities (41,000 times higher external efficiency compared with bare CdS), in which the lowest-order whispering gallery mode is engineered to concentrate light in the nonlinear material while minimizing Ohmic losses. The directional nonlinear signal is redirected into another waveguide, which is then utilized to configure an optical router that can potentially serve as a tunable coherent light source to enable on-chip signal processing for integrated nanophotonic systems.

Emerging two-dimensional semiconductor materials possess a giant second order nonlinear response due to excitonic effects while the monolayer thickness of such active materials limits their use in practical nonlinear devices. Here, we report 3300 times optomechanical enhancement of second harmonic generation from a MoS2 monolayer in a doubly resonant on-chip optical cavity. We achieve this by engineering the nonlinear light-matter interaction in a microelectro-mechanical system enabled optical frequency doubling device based on an electrostatically tunable Fabry-Perot microresonator. Our versatile optomechanical approach will pave the way for next generation efficient on-chip tunable light sources, sensors, and systems based on molecularly thin materials.

The field of plasmonics has attracted considerable attention in recent years because of potential applications in various fields such as nanophotonics, photovoltaics, energy conversion, catalysis, and therapeutics. It is becoming increasing clear that intrinsic high losses associated with plasmons can be utilized to create new device concepts to harvest the generated heat. It is therefore important to design cavities, which can harvest optical excitations efficiently to generate heat. We report a highly engineered nanowire cavity, which utilizes a high dielectric silicon core with a thin plasmonic film (Au) to create an effective metallic cavity to strongly confine light, which when coupled with localized surface plasmons in the nanoparticles of the thin metal film produces exceptionally high temperatures upon laser irradiation. Raman spectroscopy of the silicon core enables precise measurements of the cavity temperature, which can reach values as high as 1000 K. The same Si-Au cavity with enhanced plasmonic activity when coupled with TiO nanorods increases the hydrogen production rate by ∼40% compared to similar Au-TiO system without Si core, in ethanol photoreforming reactions. These highly engineered thermoplasmonic devices, which integrate three different cavity concepts (high refractive index core, metallo-dielectric cavity, and localized surface plasmons) along with the ease of fabrication demonstrate a possible pathway for designing optimized plasmonic devices with applications in energy conversion and catalysis.

Our experiments on a transformer oil-based nanofluid (NF) with ZnO nanoparticles reveal a higher relative permittivity than that of pure transformer oil. Meanwhile, the relative permittivity of ZnO NF presents a linear increase with nanoparticle volumetric concentration and a linear decrease with ambient temperature. A model based on nanoparticle polarization is proposed to investigate the mechanisms of NF relative permittivity. Analysis of the presented polarization model suggests that the value of the NF relative permittivity is dominantly determined by transformer oil, while the higher relative permittivity of NFs compared with that of pure oil is mainly caused by nanoparticle inner polarization.

No abstract

Probability density function (PDF) control strategy investigates the controller design approaches where the random variables for the stochastic processes were adjusted to follow the desirable distributions. In other words, the shape of the system PDF can be regulated by controller design.Different from the existing stochastic optimization and control methods, the most important problem of PDF control is to establish the evolution of the PDF expressions of the system variables. Once the relationship between the control input and the output PDF is formulated, the control objective can be described as obtaining the control input signals which would adjust the system output PDFs to follow the pre-specified target PDFs. Motivated by the development of data-driven control and the state of the art PDF-based applications, this paper summarizes the recent research results of the PDF control while the controller design approaches can be categorized into three groups: (1) system model-based direct evolution PDF control; (2) model-based distribution-transformation PDF control methods and (3) data-based PDF control. In addition, minimum entropy control, PDF-based filter design, fault diagnosis and probabilistic decoupling design are also introduced briefly as extended applications in theory sense.

Ultrabroadband laser sources are highly desirable in a wide variety of modern science disciplines ranging from physics, chemistry and materials science to information communications and processing. Here we present the design and fabrication of a chirped periodically poled lithium niobate (CPPLN) nonlinear photonic crystal that supports multiple orders of quasiphase matching with finite bandwidth and allows for the simultaneous broadband generation of second and third harmonics with high conversion efficiency. Moreover, the chirp rate has a significant influence on the conversion efficiency and bandwidth. The CPPLN scheme offers a promising approach for the construction of short-wavelength laser sources and enables the generation of the three primary colors-red, green and blue-from a single crystal, which may have potential applications in large-screen laser displays. Keywords: chirped periodically poled lithium niobate; quasiphase matching; second-harmonic generation; third-harmonic generation INTRODUCTION Ultrabroadband laser sources are highly desirable in a wide variety of modern science disciplines ranging from physics, chemistry and materials science to information communications and processing. Laser gain media that are capable of short-pulse generation are available but limited, and they cover only a small portion of the optical spectrum. Shortly after the creation of the first laser in 1960, the door to nonlinear optics was opened because of the discovery of second-harmonic generation (SHG).1 Broad-bandwidth and high-conversion-efficiency SHG, third-harmonic generation (THG), higher-order-harmonic generation and various frequency-mixing and parametric-conversion processes have all provided fascinating routes toward the considerable expansion of the spectral range of laser sources.To realize high-efficiency SHG, THG and other optical parametric processes, nonlinear optical materials are required to simultaneously satisfy the phase-matching condition and possess large nonlinear optical coefficients in the phase-matching direction. Although many natural nonlinear crystals have large nonlinear coefficients in certain directions, proper phase matching cannot always be achieved because of the dispersion of the material. Thus, the optical birefringent properties of certain birefringent nonlinear crystals are often utilized to compensate for the material dispersion and achieve phase matching. However, the stringent conditions for birefringent phase matching greatly limit the extension of the optical frequency. As an alternative approach, quasiphase matching (QPM), which was first proposed in 1962, 2 launched a new era in nonlinear optics because of several advantages it offers over conventional birefringence phase matching in the frequency-conversion process. These advantages include phase matching in materials that have high nonlinear optical coefficients but

No abstract