Spin-Momentum-Locked Edge Mode for Topological Vortex Lasing.

Spin-momentum locking is a direct consequence of bulk topological order and provides a basic concept to control a carrier's spin and charge flow for new exotic phenomena in condensed matter physics. However, up to date the research on spin-momentum locking solely focuses on its in-plane transport properties. Here, we report an emerging out-of-plane radiation feature of spin-momentum locking in a non-Hermitian topological photonic system and demonstrate a high performance topological vortex laser based on it. We find that the gain saturation effect lifts the degeneracy of the paired counterpropagating spin-momentum-locked edge modes enabling lasing from a single topological edge mode. The near-field spin and orbital angular momentum of the topological edge mode lasing has a one-to-one far-field radiation correspondence. The methodology of probing the near-field topology feature by far-field lasing emission can be used to study other exotic phenomena. The device can lead to applications in superresolution imaging, optical tweezers, free-space optical sensing, and communication.

Stable, high-performance sodium-based plasmonic devices in the near infrared.

Plasmonics enables the manipulation of light beyond the optical diffraction limit1-4 and may therefore confer advantages in applications such as photonic devices5-7, optical cloaking8,9, biochemical sensing10,11 and super-resolution imaging12,13. However, the essential field-confinement capability of plasmonic devices is always accompanied by a parasitic Ohmic loss, which severely reduces their performance. Therefore, plasmonic materials (those with collective oscillations of electrons) with a lower loss than noble metals have long been sought14-16. Here we present stable sodium-based plasmonic devices with state-of-the-art performance at near-infrared wavelengths. We fabricated high-quality sodium films with electron relaxation times as long as 0.42 picoseconds using a thermo-assisted spin-coating process. A direct-waveguide experiment shows that the propagation length of surface plasmon polaritons supported at the sodium-quartz interface can reach 200 micrometres at near-infrared wavelengths. We further demonstrate a room-temperature sodium-based plasmonic nanolaser with a lasing threshold of 140 kilowatts per square centimetre, lower than values previously reported for plasmonic nanolasers at near-infrared wavelengths. These sodium-based plasmonic devices show stable performance under ambient conditions over a period of several months after packaging with epoxy. These results indicate that the performance of plasmonic devices can be greatly improved beyond that of devices using noble metals, with implications for applications in plasmonics, nanophotonics and metamaterials.

A high-performance topological bulk laser based on band-inversion-induced reflection.

Topological insulators are materials that behave as insulators in the bulk and as conductors at the edge or surface due to the particular configuration of their bulk band dispersion. However, up to date possible practical applications of this band topology on materials' bulk properties have remained abstract. Here, we propose and experimentally demonstrate a topological bulk laser. We pattern semiconductor nanodisk arrays to form a photonic crystal cavity showing topological band inversion between its interior and cladding area. In-plane light waves are reflected at topological edges forming an effective cavity feedback for lasing. This band-inversion-induced reflection mechanism induces single-mode lasing with directional vertical emission. Our topological bulk laser works at room temperature and reaches the practical requirements in terms of cavity size, threshold, linewidth, side-mode suppression ratio and directionality for most practical applications according to Institute of Electrical and Electronics Engineers and other industry standards. We believe this bulk topological effect will have applications in near-field spectroscopy, solid-state lighting, free-space optical sensing and communication.

High Performance Plasmonic Nanolasers with External Quantum Efficiency Exceeding 10.

Plasmonic nanolasers break the diffraction limit for an optical oscillator, which brings new capabilities for various applications ranging from on-chip optical interconnector to biomedical sensing and imaging. However, the inevitably accompanied metallic absorption loss could convert the input power to heat rather than radiations, leading to undesired low external quantum efficiency and device degradation. To date, direct characterization of quantum efficiency of plasmonic nanolasers is still a forbidden task due to its near-field surface plasmon emissions, divergent emission profile, and the limited emission power. Here, we develop a method to characterize the external quantum efficiency of plasmonic nanolasers by synergizing experimental measurement and theoretical calculation. With systematical device optimization, we demonstrate high performance plasmonic nanolasers with external quantum efficiency exceeding 10% at room temperature. This work fills in a missing yet essential piece of key metrics of plasmonic nanolasers. The demonstrated high external quantum efficiency of plasmonic nanolasers not only clarifies the long-standing debate, but also endorses the exploration of them in various practical applications such as near-field spectroscopy and sensing, integrated optical interconnects, solid-state lighting, and free-space optical communication.

Unusual scaling laws for plasmonic nanolasers beyond the diffraction limit.

Plasmonic nanolasers are a new class of amplifiers that generate coherent light well below the diffraction barrier bringing fundamentally new capabilities to biochemical sensing, super-resolution imaging, and on-chip optical communication. However, a debate about whether metals can enhance the performance of lasers has persisted due to the unavoidable fact that metallic absorption intrinsically scales with field confinement. Here, we report plasmonic nanolasers with extremely low thresholds on the order of 10 kW cm-2 at room temperature, which are comparable to those found in modern laser diodes. More importantly, we find unusual scaling laws allowing plasmonic lasers to be more compact and faster with lower threshold and power consumption than photonic lasers when the cavity size approaches or surpasses the diffraction limit. This clarifies the long-standing debate over the viability of metal confinement and feedback strategies in laser technology and identifies situations where plasmonic lasers can have clear practical advantage.

Imaging the dark emission of spasers.

Spasers are a new class of laser devices with cavity sizes free from optical diffraction limit. They are an emergent tool for various applications, including biochemical sensing, superresolution imaging, and on-chip optical communication. According to its original definition, a spaser is a coherent surface plasmon amplifier that does not necessarily generate a radiative photon output. However, to date, spasers have only been studied with scattered photons, and their intrinsic surface plasmon emission is a "dark" emission that is yet to be revealed because of its evanescent nature. We directly image the surface plasmon emission of spasers in spatial, momentum, and frequency spaces simultaneously. We demonstrate a nanowire spaser with a coupling efficiency to plasmonic modes of 74%. This coupling efficiency can approach 100% in theory when the diameter of the nanowire becomes smaller than 50 nm. Our results provide clear evidence of the surface plasmon amplifier nature of spasers and will pave the way for their various applications.

Use of random forest in FTIR analysis of LDL cholesterol and tri-glycerides for hyperlipidemia.

A quantitative determination method for the diagnosis of hyperlipidemia was developed using Fourier transform infrared (FTIR) spectroscopy. Random forest (RF) was demonstrated as a potential multivariate algorithm for the FTIR analysis of low-density lipoprotein cholesterol (LDL-C) and tri-glycerides (TG) in human serum samples. The informative wavebands for LDL-C and TG were selected based on the Gini importance. The selected wavebands were mainly within the fingerprint region. The RF modeling results were better than those derived using PLS in validation process, because the chance for over-fitting was possibly eliminated in RF algorithm. ARF also demonstrated favorable results in the test process. The prospective model exhibited a higher than 90% true prediction in negative/positive properties for male and female samples. These clinical statistical results indicated the optimization of RF algorithm performed accurately in the FTIR determination of LDL-C and TG. RF is evaluated as a promising tool for diagnosing and controlling hyperlipidemia in populations. The parameter optimization methodology is useful in the improving model accuracy using FTIR spectroscopic technology.

[Multidimensional Scaling Linear Regression Applied to FTIR Spectral Quantitative Analysis of Clinical Parameters of Human Blood Serum].

In the present paper it was proposed to establish multidimensional scaling linear regression (MDS-MLR) models by combining multidimensional scaling (MDS) with multiple linear regression (MLR), in which MDS owns the ability of dimensionality reduction on spectral variables. Thus the informative spectral wavelengths can be selected for each of the 4 clinical parameters (i. e. glucose, LDL cholesterol, triglycerides and urea) by MDS-MLR method, and the effect of spectral colinearity can be restrained, so that the calibration models can be optimized. Experiments showed that the MDS-MLR models will allow to produce appreciated modeling results when combined with the preprocessing method of moving average (MA). The optimized models were verified by the samples in validation set, and the validating correlation coefficients for each clinical parameter were all upper than 0. 9. These results indicated that FTIR predicted values and the biochemical values of each clinical parameter were highly correlated, which demonstrated that MDS-MLR method has the potential of being applied to the FTIR spectroscopic analysis of human serum. FTIR rapid determination technology combined with the MDS-MLR modeling method is expected to realize the rapid assessment of human health and sub-health level.

[Spectroscopic methods applied to component determination and species identification for coffee].

Spectroscopic analysis was applied to the determination of the nutrient quality of ground, instant and chicory coffees. By using inductively coupled plasma atomic emission spectrometry (ICP-ES), nine mineral elements were determined in solid coffee samples. Caffeine was determined by ultraviolet (UV) spectrometry and organic matter was investigated by Fourier transform infrared (FTIR) spectroscopy. Oxidation-reduction titration was utilized for measuring the oxalate. The differences between ground coffee and instant coffee was identified on the basis of the contents of caffeine, oxalate and mineral elements. Experimental evidence showed that, caffeine in instant coffee was 2-3 times higher than in ground coffee. Oxalate in instant coffee was significantly higher in ground coffee. Mineral elements of Mg, P and Zn in ground coffee is lower than in instant coffee, while Cu is several times higher. The mineral content in chicory coffee is overall lower than the instant coffee. In addition, we determined the content of Ti for different types of coffees, and simultaneously detected the elements of Cu, Ti and Zn in chicory coffee. As a fast detection technique, FTIR spectroscopy has the potential of detecting the differences between ground coffee and instant coffee, and is able to verify the presence of caffeine and oxalate.