Reduction of relative intensity noise in a diamond Raman laser.

The relative intensity noise (RIN) characteristics of a continuous-wave diamond Raman laser are investigated for the first time. The results reveal the parasitic stimulated Brillouin scattering (SBS) that usually occurred with higher-order spatial modes in the diamond Raman resonator is a pivotal factor impacting the Raman longitudinal modes and deteriorating the RIN level. The diamond Raman laser automatically switches to single-longitudinal-mode operation and the RIN level is significantly decreased in the frequency range of 200 Hz to 1 MHz after the parasitic SBS is effectively suppressed through inserting a spatial aperture or a χ(2) nonlinear crystal into the cavity. Due to the introduction of additional nonlinear loss to the high intensity Raman fluctuations and the non-lasing spontaneous Raman modes, the χ(2) nonlinear crystal enables better performance in the RIN-level reduction compared to the spatial aperture which can only achieve SBS inhibition. The RIN reduction routes are well suited for various crystalline Raman media to achieve high power and low intensity noise laser at different wavelengths.

Topological laser with higher-order corner states in the 2-dimensional Su-Schrieffer-Heeger model.

A nonlinear non-Hermitian topological laser system based on the higher-order corner states of the 2-dimensional (2D) Su-Schrieffer-Heeger (SSH) model is investigated. The topological property of this nonlinear non-Hermitian system described by the quench dynamics is in accordance with that of a normal 2D SSH model. In the topological phase, all sites belonging to the topological corner states begin to emit stable laser light when a pulse is given to any one site of the lattice, while no laser light is emitted when the lattice is in the trivial phase. Furthermore, the next-nearest-neighbor (NNN) couplings are introduced into the strong-coupling unit cells of the 2D SSH model, which open a band gap in the continuous band structure. In the topological phase, similar to the case of 2D SSH model without NNN couplings, the corner sites can emit stable laser light due to the robustness of the higher-order corner states when the NNN couplings are regarded as the perturbation. However, amplitude of the stimulated site does not decay to zero in the trivial phase, because the existence of the NNN couplings in the strong-coupling unit cells make the lattice like one in the tetramer limit, and a weaker laser light is emitted by each corner.

A Linearly Polarized Wavelength-Tunable Q-Switched Fiber Laser with a Narrow Spectral Bandwidth of 112 MHz.

A tunable and narrow-bandwidth Q-switched ytterbium-doped fiber (YDF) laser is investigated in this paper. The non-pumped YDF acts as a saturable absorber and, together with a Sagnac loop mirror, provides a dynamic spectral-filtering grating to achieve a narrow-linewidth Q-switched output. By adjusting an etalon-based tunable fiber filter, a tunable wavelength from 1027 nm to 1033 nm is obtained. When the pump power is 1.75 W, the Q-switched laser pulses with a pulse energy of 10.45 nJ, and a repetition frequency of 11.98 kHz and spectral linewidth of 112 MHz are obtained. This work paves the way for the generation narrow-linewidth Q-switched lasers with tunable wavelengths in conventional ytterbium, erbium, and thulium fiber bands to address critical applications such as coherent detection, biomedicine, and nonlinear frequency conversion.

Characterization of a Novel Artemisinin Algicidal Particle and Its Inhibitory Effect on Microcystis aeruginosa.

A new artemisinin sustained-release particle (ASP) was developed that significantly inhibits Microcystis aeruginosa (M. aeruginosa) growth. The physical and chemical properties of ASPs were characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), differential scanning calorimetry, and thermogravimetry (DSC-TG). The results demonstrated that ASPs are thermally stable and have sustained-release properties. On the sixth day, the ASPs (0.2 g L-1) inhibited M. aeruginosa with an inhibition rate (IR) greater than 70%. Additionally, ASPs inhibited M. aeruginosa without increasing microcystin-LR release (MC-LR). This research offers a novel approach to the management of cyanobacterial blooms.

Squeezed light generated with hyperradiance without nonlinearity.

We propose that the squeezed light accompanied by hyperradiance is induced by quantum interference in a linear system consisting of a high-quality optical cavity and two coherently driven two-level qubits. When two qubits are placed in the cavity with a distance of integer multiple and one-half of wavelengths (i.e., they have the opposite coupling coefficient to the cavity), we show that squeezed light is generated in the hyperradiance regime under the conditions of strong coupling and weak driving. Simultaneously, Klyshko's criterion alternates up and down at unity when the photon number is even or odd. Moreover, the orthogonal angles of the squeezed light can be controlled by adjusting the frequency detuning between the driving field and the qubits. It can be implemented in a variety of quantum systems, including but not limited to two-level systems such as atoms, ions, quantum dots in single-mode cavities.

Chiral interaction of an atom in a sandwiched waveguide.

The chiral interaction between light and matter is mainly caused by the spin-momentum locking and makes the chiral quantum optics enter a vigorous development stage. Here, we explore the condition of the perfect chiral interaction between an atom possessing circular dipole and the surface plasmon polariton (SPP) mode. The realization of the perfect chiral interaction must satisfy the following two conditions at the same time. First, the SPP mode should possess the transverse circular polarization; and second, the atom decays mainly into the SPP mode, while the decay through other channel can be ignored. In this paper, we adopt a simple but effective structure to satisfy both of requirements, which is the sandwiched waveguide made of metal. We found that the transverse circular polarization of SPP mode might be achieved within the structure possessing multiple interfaces instead of the interface separating two semi-infinite materials. In our model, the decay rate into SPP mode overwhelms that through traveling wave, which provides higher quantum efficiency. What's more, we found that only the symmetric TM-polarized SPP mode might get the transverse circular polarization. For the sandwiched structure containing metal, the existence of two SPP modes weakens the overall chiral interaction. However, the structure containing left-handed materials (LHMs), which can only support one symmetric TM-polarized SPP mode, can get the nearly perfect chiral interaction. We measure the chiral interaction through the decay rate, radiation field distribution and the unidirectional rate through the energy flux. Our work provides a reference for exploring the perfect chiral interaction in more complex structures and has potential and wide applicability to other optical processes.

Interaction of two quantum dots mediated by edge modes of coupled-cavity arrays.

Topological photonics is a hot topic in recent years. We combine it with the quantum optics and explore the dynamics of two quantum dots (QDs) separated by the finite coupled-cavity arrays (CCAs). The finite CCAs possessing the alternating hopping strengths will lead to the existence of the topological protected edge modes, also called zero energy modes, when the boundaries leave the weak hopping at two ends. Due to the two edge modes, i.e., symmetric and antisymmetric, with nearly degenerate frequencies, the dynamics of two QDs coupled to the cavities at both ends exhibit complicated behaviors. When the CCAs are composed of a large number of cavities, there are two kinds of phenomena: if the coupling between QDs and cavity is weak, two edge modes will cancel each other out and isolate two QDs deeply; if the coupling between QDs and cavities is large compared with hopping strength, the edge mode disappears and two QDs can be connected through extend modes. Importantly, when the CCAs are formed by a small number of cavities, energy can be transferred to each other between two QDs through the edge modes. Such energy transfer is topologically protected, and the period is long and easily controlled. We also investigate the effects of topologically protected quantum entangled states on such system and find that the quantum entanglement can be well kept or generated for appropriate choices of system parameters and initial states. The investigations enrich the manifestation of topological physics and are helpful to apply the topological protection to quantum computation and quantum communication.

Enantioselective Reductive Cyanation and Phosphonylation of Secondary Amides by Iridium and Chiral Thiourea Sequential Catalysis.

The combination of transition-metal catalysis and organocatalysis increasingly offers chemists opportunities to realize diverse unprecedented chemical transformations. By combining iridium with chiral thiourea catalysis, direct enantioselective reductive cyanation and phosphonylation of secondary amides have been accomplished for the first time for the synthesis of enantioenriched chiral α-aminonitriles and α-aminophosphonates. The protocol is highly efficient and enantioselective, providing a novel route to the synthesis of optically active α-functionalized amines from the simple, readily available feedstocks. In addition, the reactions are scalable and the thiourea catalyst can be recycled and reused.

Ten-Gram-Scale Facile Synthesis of Organogadolinium Complex Nanoparticles for Tumor Diagnosis.

The market of available contrast agents for clinical magnetic resonance imaging (MRI) has been dominated by gadolinium (Gd) chelates based T1 contrast agents for decades. However, there are growing concerns about their safety because they are retained in the body and are nephrotoxic, which necessitated a warning by the U.S. Food and Drug Administration against the use of such contrast agents. To ameliorate these problems, it is necessary to improve the MRI efficiency of such contrast agents to allow the administration of much reduced dosages. In this study, a ten-gram-scale facile method is developed to synthesize organogadolinium complex nanoparticles (i.e., reductive bovine serum albumin stabilized Gd-salicylate nanoparticles, GdSalNPs-rBSA) with high r1 value of 19.51 mm-1 s-1 and very low r2 /r1 ratio of 1.21 (B0 = 1.5 T) for high-contrast T1 -weighted MRI of tumors. The GdSalNPs-rBSA nanoparticles possess more advantages including low synthesis cost (≈0.54 USD per g), long in vivo circulation time (t1/2 = 6.13 h), almost no Gd3+ release, and excellent biosafety. Moreover, the GdSalNPs-rBSA nanoparticles demonstrate excellent in vivo MRI contrast enhancement (signal-to-noise ratio (ΔSNR) ≈ 220%) for tumor diagnosis.

Single photon polarization conversion via scattering by a pair of atoms.

The single photon scattering in one-dimensional waveguide coupled to two separated atoms is investigated. The first atom is considered as a Λ system and the second one is taken as V -type configuration. The analytical expressions of the single photon scattering spectra are obtained. The calculated results show that the polarization conversion of single photon can be realized by controlling the distance between the two atoms due to the interference effects. The conversion efficiency can reach unit in the ideal case. Furthermore, the polarization conversion of the single photon also depends on the initial state of the Λ system. The influences of dissipations on the single photon polarization conversion are also shown.

Repulsive Casimir force between hyperbolic metamaterials.

The Casimir force between electric and magnetic hyperbolic metamaterial slabs is investigated. Due to hyperbolic dispersion, the electromagnetic features of these metamaterials along the optical axis are different from those perpendicular to the optical axis; consequently, these features contribute differently to the Casimir effect. The repulsive Casimir force is formed between electric and magnetic hyperbolic metamaterial slabs; moreover, hyperbolic dispersion can enhance the repulsive effect. However, by utilizing the extremely anisotropic behavior of hyperbolic metamaterials and changing the separation distance between the two slabs, the restoring Casimir force emerges. Additionally, by considering the dispersion of both the permittivity and the permeability of hyperbolic metamaterials, the Casimir force reaches several equilibrium points at different separation distances. Furthermore, the Casimir force at room temperature is discussed. Although the temperature can weaken the effect of the restoring Casimir force, stable equilibria may remain upon choosing suitable filling factors. This work shows that hyperbolic metamaterials have potential applications in micro- and nanoelectromechanical systems, especially for maintaining stability and overcoming adhesion problems.

Matter-Wave-Optical-Wave Mixing-Induced Transparency and a Nonhyperbolic Matter-Wave Quasisoliton in Quantum Gases.

The realization of atomic quantum gases has brought out surprising effects that have no correspondence in nonlinear optics with thermal gases, presenting intriguing and exciting challenges to the research discipline of nonlinear optics which has matured since the invention of the laser. Here, we show an unexpected optical wave-mixing gain cancellation effect in a quantum gas that restricts an, otherwise, strongly enhanced backward-propagating light-matter wave-mixing process. This results in a wave-mixing induced transparency and a nonhyperbolic quasi-matter-wave soliton that opens new research opportunities in hydrodynamic fluid research of degenerate quantum gases, such as phonon scattering in a two-dimensional sonic black hole horizon.

Enhanced displacements in reflected beams at hyperbolic metamaterials.

We examine the Goos-Hänchen (G-H) shift of a Gaussian beam reflected on a thin slab of Ag/TiO2 hyperbolic multilayer metamaterial (HMM). The HMM is modeled using the effective medium theory which yields the anisotropic dielectric functions of the HMM. The G-H shifts can be very large on the surface of the HMM. It can be about 40 µm which are far bigger than the G-H shifts on the usual materials like metals and dielectrics. The enhancement is due to the excitation of the Brewster modes in HMM. Such Brewster modes in HMM have a well-defined frequency-dependent line shape. We relate the the half width at half maximum of the G-H shift to the imaginary part of the complex frequency of the Brewster mode. Moreover, we also present results for the Imbert-Fedorov shifts as well as the spin Hall effect of light on the surface of a thin HMM slab. We show that the spin Hall effect on the HMM slab is much more pronounced than that on the surface of metal. Thus a thin HMM slab can be used to enhance the lateral displacements, which can have many interesting applications for optical devices.

Dynamic lossless polarization gate using a coherently prepared atomic medium.

We propose a dynamic lossless all-optical polarization gate using coherently prepared atomic media. We show that the loss/gain of two circularly polarized components of a linearly polarized probe field can be simultaneously eliminated by locking the power of the pump field and the external magnetic field intensity simultaneously. Using the polarization selective Kerr phase shift method, we can write π/2 (-π/2) phase shift to the right (left) circularly polarized component of the linearly polarized probe field with a choice of "magic" wavelength for the probe field. Consequently, the linear polarization state for the probe field acquires a 90° rotation at the exit of the medium. The scheme proposed in this Letter is helpful for applications in optical and quantum information processing and computation.

Versatile, dynamically balanced low-noise optical-field manipulator using a coherently prepared atomic medium.

We propose a versatile dynamic optical-field manipulator using a coherently prepared atomic medium. We show that by locking the pump power change with the two-photon detuning, a π-phase shifting can be realized with unit probe fidelity in a broad two-photon detuning range. The two-photon-insensitive π-phase-shift mode with significantly reduced fluctuation makes this scheme an attractive system for low-noise phase-gate operations.

Phylogenetic position of Guihaiothamnus (Rubiaceae): its evolutionary and ecological implications.

Guihaiothamnus (Rubiaceae) is an enigmatic, monotypic genus endemic to southwestern China. Its generic status has never been doubted because it is morphologically unique by having rosette habit, showy, long-corolla-tubed flowers, and multi-seeded indehiscent berry-like fruits. The genus has been postulated to be a relict in the broad-leaved forests of China, and to be related to the genus Wendlandia, which was placed in the subfamily Cinchonoideae and recently classified in the tribe Augusteae of the subfamily Dialypetalanthoideae. Using combined evidence from palynology, cytology, and DNA sequences of nuclear ITS and four plastid markers (rps16, trnT-F, ndhF, rbcL), we assessed the phylogenetic position of Guihaiothamnus in Rubiaceae. Our molecular phylogenetic analyses placed the genus deeply nested within Wendlandia. This relationship is corroborated by evidence from palynology and cytology. Using a relaxed molecular clock method based on five fossil records, we dated the stem age of Wendlandia to be 17.46 my and, the split between G. acaulis and related Wendlandia species in southwestern China to be 2.11mya. This young age, coupled with the derived position in Wendlandia, suggests an evolutionary derivation rather than an evolutionary relict of G. acaulis. Its rosette habit and large showy flowers, which are very distinctive from other Wendlandias, are interpreted as a result of recent rapid adaptation to rock and cliff habitats.

Hybrid quantum-well system for wavelength-channel selection.

We consider a hybrid quantum-well structure consisting of regions whose properties alternate between active Raman gain and electromagnetically induced transparency. We present both analytical and numerical results that indicate a large light beam defection using spatially inhomogeneous pump and control lasers. We show well-isolated on-chip wavelength selection or channeling capabilities without light field attenuation or distortion, demonstrating the advantages of the system for possible important applications in integrated circuits for optical telecommunications.

Highly efficient counter-propagation-beams narrow-band ultraviolet frequency conversion in a quantum gas.

We show that highly efficient ultraviolet frequency up conversion can be established in a single-component quantum gas in the counter-propagating weak pump beam geometry where no frequency up conversion can occur in a normal gas. We also show that all light-wave mixing and scattering processes in quantum gases originating from elementary excitations characterized by efficient collective atomic recoil motion are stimulated Raman/hyper-Raman in nature.

Light-wave mixing and scattering with quantum gases.

We present a semiclassical theoretical framework on light-wave mixing and scattering with single-component quantum gases. We show that these optical processes originating from elementary excitations with dominant collective atomic recoil motion are stimulated Raman or hyper-Raman in nature. In the forward direction the wave-mixing process, which is the most efficient process in normal gases, is strongly reduced by the condensate structure factor even though the Bogoliubov dispersion relation automatically compensates the optical-wave phase mismatch. In the backward direction, however, the free-particle-like condensate structure factor and Bogoliubov dispersion result in highly efficient light-wave mixing and collective atomic recoil motion that are enhanced by a stimulated hyper-Raman gain and a very narrow two-photon motional state resonance.

An Ingestible Pill With CMOS Fluorescence Sensor Array, Bi-Directional Wireless Interface and Packaged Optics for in-Vivo Bio-Molecular Sensing.

The article presents for the first time a pill-based ingestible electronics with CMOS integrated multiplexed fluorescence bio-molecular sensor arrays, bi-directional wireless communication and packaged optics in a FDA-approved capsule for in-vivo bio-molecular sensing. The silicon chip integrates both the sensor array, and the ultra-low-power (ULP) wireless system that allows offloading sensor computing to an external base station that can reconfigure the sensor measurement time, and its dynamic range, allowing optimized high sensitivity measurement under low power consumption. The integrated receiver achieves -59 dBm receiver sensitivity dissipating 121 µW of power. The integrated transmitter operates in a dual mode FSK/OOK delivering -15 dBm of power. The 15-pixel fluorescence sensor array follows an electronic-optic co-design methodology and integrates the nano-optical filters with integrated sub-wavelength metal layers that achieves high extinction ratio (39 dB), thereby eliminating the need for bulky external optical filters. The chip integrates photo-detection circuitry and on-chip 10-bit digitation, and achieves measured sensitivity of 1.6 attomoles of fluorescence labels on surface, and between 100 pM to 1 nM of target DNA detection limit per pixel. The complete package includes a CMOS fluorescent sensor chip with integrated filter, a prototyped UV LED and optical waveguide, functionalized bioslip, off-chip power management and Tx/Rx antenna that fits in a standard FDA approved capsule size 000.