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Local interface response effects are neglected based on the traditional electromagnetic boundary conditions (EMBCs) in an abrupt interface model. In this study, generalized nanoscale EMBCs are derived with interface response functions (IRFs) representing field inhomogeneity across the interface based on integral Maxwell’s equations. They are rewritten in two different forms that correspond to the equivalent abrupt interface models with interface-induced dipoles or charges and currents. Interesting behaviors of Brewster angle shifting, non-extinction at Brewster angle, and unique absorption or gain effects are revealed based on the advanced Fresnel formula. IRFs-controlled GH-shift and angular GH-shift of a Gaussian beam near the Brewster angles are generated by the gradient interface. These unique phenomena provide some guidance for measuring the IRFs and expanding interface photonics at the nanoscale.

Classical electromagnetic boundary conditions (EMBCs) fail to describe quantum interface phenomena at nanoscale. Here, we construct the interface model with a transition layer describing the electromagnetic field inhomogeneity across the interface. Generalized nanoscale EMBCs are derived by introducing the magnetic interfacial response functions (IRFs) and are rewritten as three different forms based on Maxwell's equations in first order approximation. The corresponding Fresnel formula are further used to analyze the interfacial photonic phenomenon, demonstrating interesting behaviors of Brewster angle shifting, non-extinction at Brewster angle and distinctive non-classical absorption or gain effect at Brewster angle and the total internal reflection angles. IRFs-controlled GH-shifts of Gaussian beam near Brewster angle are generated by the non-classical interface. These unique phenomena give us some guidance to measure the IRFs and expand interface photonics in nanoscale., Comment: 13 pages, 3 figures

A ring-shaped random laser in momentum space is designed by directly coupling a random laser with a commercial optical fiber. By using a simple approach of selectively coating the random gain layer on the surface of the fiber, red and yellow random lasers are respectively achieved with low threshold values and a good emission direction due to the guiding role of optical fibers. The unique coupling mechanism leads to a random laser with a ring shape in momentum space, which is an excellent illuminating source for high-quality imaging with an extremely low speckle noise. More importantly, a triple-state color-switchable random laser with yellow, red and yellow-red dual-colors can be flexible, and is obtained by simply moving the pump position. The results may promote the practical applications of random lasers in the fields of sensing, in vivo biological imaging, and high brightness full-field illumination.

Line width-tunable lasers have wide applications in the fields of high-resolution spectroscopy, optical communications, and other industry and scientific research. Here, manipulating plasmonic scat...

Bound states in the continuum (BICs) have been observed in a variety of systems. A plasmonic BIC offers interesting opportunities, since a surface plasmon is known to confine light to the nanometer scale. However, the observation and manipulation of plasmonic BICs is a challenge due to the intrinsic loss of metals. Here, we study plasmonic BICs in the visible range in a one-dimensional all-metallic grating. First, by tuning the resonances of localized and propagating surface plasmon modes to resonance, we successfully observe symmetry-protected plasmonic BICs in an all-metallic system. Next, by continuously tuning the localized mode, we demonstrate topological band inversion characterized by a Zak phase transition. In addition, we engineer off-\ensuremath{\Gamma}-point BICs and confirm their formation mechanism. Finally, we experimentally determine that the quality ($Q$) factor of a 10-groove structure can exceed 60, about one order of magnitude greater than conventional metallic structures. The simulations reveal that, with more grooves, the $Q$ factor can be over 200. The plasmonic BICs in the visible range demonstrated in this paper pave the way to promising applications in lasers, sensors, light-matter interactions, nonlinear optics, and quantum optics.

The color and/or chromaticity controllability of random lasing is a key factor to promote practical applications of random lasers as high luminance sources for speckle-free imaging. Here, white coherent random lasing with tunable chromaticity is obtained by using broadband enhancement Au-Ag nanowires as scatterers and the resonance energy transfer process between different dyes in the capillary microfluidic channel. Red, green and blue random lasers are separately fabricated with low thresholds, benefiting from the plasmonic resonance of the nanogaps and/or nanotips with random distribution and sizes within Au-Ag nanowires and positive optical feedback provided by the capillary wall. A white random laser system is then designed through reorganizing the three random lasers. And, the chromaticity of the white random laser is flexibly tunable by adjusting pump power density. In addition, the white random laser has anisotropic spectra due to the coupling role between the lasers. This characteristic is then utilized to obtain different random lasing with different chromaticity over a broad visible range. The results may provide a basis for applying random laser in the field of high brightness illumination, biomedical imaging, and sensors.

By coupling pyroelectric effect and photoelectric effect, pyro-phototronic effect is proposed to effectively modulate photon response characteristics of the detector with p-n junction. Here, tuning role of chopper frequency on pyroelectric effect in p-n junction is revealed by demonstrating the dynamic performances of pyro-phototronic effect based UV photodetectors (PDs) under different power densities and different bias voltages. Different from the traditional pyroelectric detectors without p-n junction, the pyro-phototronic effect based PDs possess the optimal response frequency that is strong dependent on the stimuli power density and the external bias voltage. With the power density increasing from 7.9 × 10-5 to 1.5 × 10-3 W cm-2, the optimal chopper frequency of the self-powered PD increases from 50 Hz to 200 Hz. By changing the bias voltages, the transient currents have a group of maximal values for different chopper frequencies at a same voltage of −0.2 V when the detector is illuminated by UV light with a power density of 1.8 × 10-2 W cm-2. The results present the fundamental working characteristics of the pyro-phototronic effect based PD and provide guidance for its future applications in IR imaging, fast detecting and smart optoelectronic systems.

The working threshold is an important parameter to assess the performance of cavity-free random lasers. Here, the temporal profile measurement is proposed as an alternative method to determine the thresholds of the surface plasmon based random lasers pumped by ns pulses based on analyzing the delay time (tDelay) and rising time (tR) of the emission signal. The obvious and slight inflection points of the curves of tDelay and tR varying with the pump power density are observed as indicators for the thresholds of random lasing and for the transition of lasing mode, respectively. The proposed method supplies consistent values to those supplied by traditional methods in frequency-domain for the random systems with different gain length. The demonstrated temporal profile approaches are free from the spectrometers and may be as a candidate for measuring the threshold of random lasers in ultrafast optics, nonlinear optics and bio-compatible optoelectronic probes.

An integrated random laser based on green materials with dissolubility and recyclability is created and demonstrated. The dissolvable and recyclable random laser (DRRL) can be dissolved in water, accompanying the decay of emission intensity and the increment in lasing threshold. Furthermore, the DRRL can be reused after the process of deionized treatment, exhibiting excellent reproducibility with several recycling processes.

Multicolor random lasing has broad potential applications in the fields of imaging, sensing, and optoelectronics. Here, silver nanoflowers (Ag NF) with abundant nanogaps are fabricated by a rapid one-step solution-phase synthesis method and are first proposed as effective broadband plasmonic scatterers to achieve different color random lasing. With abundant nanogaps and spiky tips near the surface and the interparticle coupling effect, Ag NFs greatly enhance the local electromagnetic field and induce broadband plasmonic scattering spectra over the whole visible range. The extremely low working threshold and the high-quality factor for Ag NF-based random lasers are thus demonstrated as 0.24 MW cm−2 and 11,851, respectively. Further, coherent colorful random lasing covering the visible range is realized using the dye molecules oxazine (red), Coumarin 440 (blue), and Coumarin 153 (green), showing high-quality factor of more than 10,000. All these features show that Ag NF are highly efficient scatterers for high-performance coherent random lasing and colorful random lasers.

A color-switchable random laser is designed through directly coupling random laser with a commercial optical fiber. By using a simple approach of selectively coating the random gain layer on the surface of fiber, the red and yellow random lasers are respectively achieved with low threshold and good emission direction due to the guiding role of optical fibers. Moreover, the unique coupling mechanism leads to the random lasing with ring-shape in momentum space, indicating an excellent illuminating source for high-quality imaging with an extremely low speckle noise. More importantly, random lasing with different colors can be flexible obtained by simply moving the pump position.

On-chip coherent light source has always been fascinating and intriguing due to its various potential applications. In the past decades, there has been some progress in the development of chip coherent light (e.g., nanolaser, Bose-Einstein condensation and nonlinear optical effects). However, these methods strictly depend on materials and extreme experimental conditions, and are usually not tunable. Here, a hybrid structure is designed which combines a chirped surface plasmon metasurface with a monolayer transition metal dichalcogenide (TMDC) to achieve a coherent second harmonic generation (SHG) covering the entire visible light spectrum. Using only finite number of metallic grooves, a continuous resonance tuning is obtained. By translating the metasurface in space, a space-frequency locking SHG is demonstrated. Although the Q factor of the surface plasmon cavity is low, its near-field enhancements of both fundamental and SH waves are still obvious. Significantly, the broad linewidth of plasmonic cavity leads to a large degree of overlap between adjacent localized modes, that enables the tuning of the output wavelength continuously at room temperature. Meanwhile, the exciton resonance also plays an important role. This monolithic tunable device demonstrates the potentials of 2D material-plasmon hybrid metasurface and to construct an efficient broadband tunable on-chip coherent light source.

Rapid detection of surface enhanced Raman scattering (SERS) signals is in great demand in the fields of biological medicine and environmental monitoring. Herein, a grooved silver nanoplate assembly (GSNA) with an abundance of multiscale gaps has been proposed for the first time and skillfully synthesized to act as an excellent platform for surface enhanced Raman spectroscopy with ultrafast and ultrasensitive detection. By effectively combining the hotspots effect of nanogaps and the trapping effect of gaps in the scale of subwavelength, the Raman signal was greatly enhanced by a factor of 1010 and the detection limit of Rhodamine 6G (R6G) could reach 5 × 10-13 M. Moreover, based on the perfect adsorption of the multiscale gaps, the probe molecule could be detected immediately after the analyte was mixed with the GSNA. In addition, the mixed analytes of R6G and crystal violet could be easily distinguished by Raman signal detection based on the fabricated basement. This study provides an effective SERS platform to achieve ultrafast Raman detection with ultrasensitivity in the fields of chemical analysis, biomedicine and environmental monitoring.

Self-powered ZnO/perovskite heterostructured ultraviolet (UV) photodetectors (PDs) based on the pyro-phototronic effect have been recently reported as a promising solution for energy-efficient, ultrafast-response, and high-performance UV PDs. In this study, the temperature dependence of the pyro-phototronic effect on the photo-sensing performance of self-powered ZnO/perovskite heterostructured PDs was investigated. The current responses of these PDs to UV light were enhanced by 174.1% at 77 K and 28.7% at 300 K owing to the improved pyro-phototronic effect at low temperatures. The fundamentals of the pyro-phototronic effect were thoroughly studied by analyzing the chargetransfer process and the time constant of the current response of the PDs upon UV illumination. This work presents in-depth understandings about the pyrophototronic effect on the ZnO/perovskite heterostructure and provides guidance for the design and development of corresponding optoelectronics for ultrafast photo sensing, optothermal detection, and biocompatible optoelectronic probes.

A light-self-induced pyro-phototronic effect in wurtzite ZnO nanowires is proposed as an effective approach to achieve ultrafast response ultraviolet sensing in p-Si/n-ZnO heterostructures. The relatively long response/recovery time of zinc-oxide-based ultraviolet sensors in air/vacuum has long been an obstacle to developing such detectors for practical applications. The response/recovery time and photoresponsivity are greatly improved by the pyro-phototronic effect.

A humidity-tailored film random laser is proposed and fabricated as a dye organic thin layer with Ag nanoflowers as plasmonic scatterers. By modifying the film's optical thickness with the surrounding humidity, the random lasing's wavelength and peak intensity are well regulated based on the waveguide feedback model. The peak wavelength is blue shifted from 575.18 nm to 568.43 nm and the peak intensity reduces from 3.97 × 104 to 4.0 × 103 a.u. when the air humidity changes from 18.0% to 71.4%, demonstrating the linear behaviors and better humidity sensitivity relative to that of the fluorescence, respectively. In addition, the fabricated random laser has a good time stability. These results may supply a new flexible way to design environment interaction random lasers and tailor their output performances, also promote their practical applications in the fields of smart sensing, internet of things, and environment monitoring.

ZnO based self-powered photodetector (PD) has great application potential in distributing sensor networks and internet of things. However, a large number of surface or interface states within ZnO limit its performance improvement. Here, the surface and interface states of ZnO is greatly eliminated by ultraviolet irradiation as an interfacial modification engineering. Reduction of interface states reduces ohmic resistance, also enhances the tuning role of pyro-phototronic effect. And the transient response currents of the self-powered PD are thus significantly improved with a maximal enhancement factor of more than 5900% for the 325–785 nm broadband stimulating beams. The corresponding response time is decreased to few milliseconds or sub-milliseconds. The results indicate that surface-state reduction of ZnO can effectively enhance the modifying role of pyro-phototronic effect and greatly improve the response performances of the self-powered broadband PDs with great application demands in Internet of things, broad spectral detecting and imaging, and smart optoelectronic devices.

Surface enhanced Raman spectroscopy (SERS) is a key nondestructive detecting technology with a broad application demands. However, relative low stability and homogeneity of the SERS substrate hinder its practical applications. Here, a simple and flexible approach is proposed to achieve the arrayed SERS substrates with the periodicity and local randomness by directly growing silver nanoflowers on the patterned wafer fabricated by the optical interference method. By utilizing the hotspot effect of nanogaps within/between the Ag nanoflowers, the SERS substrates demonstrate the low detecting limit of 5 × 10−10 M and 5 × 10−9 M in one-dimensional (1D) and two-dimensional (2D) pattern structures for Rhodamine 6G (R6G) probe molecule, respectively. The periodicity assures the fabricated substrate a promising reproducibility and stability. After the 1D array structure is left for 21 days, the intensity of Raman signal of R6G maintains at 80%. Moreover, the proposed method has the advantages of simple preparation, low cost, flexible tunability, and easy-fabrication large scale substrate. The results indicate that the long-range ordered silver nanoflower array structures are promising candidates for the high performance SERS substrate in chemical analysis, medicine and environment monitoring.

Hierarchical forest-like photoelectrodes were prepared by assembling nano-ZnO on an array of micro-metal dendrites, aiming to demonstrate the idea of highly efficient photon-harvesting inside a biomimetic dendrite structure. Via a facile aqueous electrochemical deposition process, the metal dendrites were deposited on both flat and wire substrates with different alignments, showing wide adaptability. A strong, broadband anti-reflection effect was observed, owing to the diffuse reflection inside the microdendrites. By increasing the dendrite height, the overall reflectivity of the metal electrode can be reduced from 75% to 45%, which could be further reduced to 12% after combining with acicular-leaf-like ZnO nanoarrays. Its applications in light-driven water splitting were successfully demonstrated. Taking advantage of the forest-like photoelectrode, we have artificially constructed an efficient photo-electrochemical system similar to plants in a forest, with photons harvested by the crown-like photoanodes in the sunshine, and synthetic reactions driven by the root-like electrode in the shadow.

A stretchable-rubber-based (SR-based) triboelectric nanogenerator (TENG) is developed that can not only harvest energy but also serve as self-powered multifunctional sensors. It consists of a layer of elastic rubber and a layer of aluminum film that acts as the electrode. By stretching and releasing the rubber, the changes of triboelectric charge distribution/density on the rubber surface relative to the aluminum surface induce alterations to the electrical potential of the aluminum electrode, leading to an alternating charge flow between the aluminum electrode and the ground. The unique working principle of the SR-based TENG is verified by the coupling of numerical calculations and experimental measurements. A comprehensive study is carried out to investigate the factors that may influence the output performance of the SR-based TENG. By integrating the devices into a sensor system, it is capable of detecting movements in different directions. Moreover, the SR-based TENG can be attached to a human body to detect diaphragm breathing and joint motion. This work largely expands the applications of TENG not only as effective power sources but also as active sensors; and opens up a new prospect in future electronics.

Linewidth-tunable lasers have great application requirements in the fields of high-resolution spectroscopy, optical communications and other industry and scientific research. Here, the switchable plasmonic scattering of the metal particles with plenty of nanogaps is proposed as an effective method to achieve linewidth-tunable random lasers. By using the nonlinear optical effect of the environment medium, the metal particles demonstrate the transition from local scattering of nanogaps with high spatial frequency to traditional Mie scattering free from detail information with increasing the pump power density. Based on these two scattering processes, random lasers can be continuously driven from a narrow-linewidth configuration exhibiting nanogap effect dominated resonances to a broad-linewidth regime of collectively coupling oscillating among nanowires (or nanoflowers), demonstrating the dynamic range of linewidth exceeds two orders of magnitude. This phenomenon may provide a platform for further studying of the conclusive mechanism of random lasing and supply a new approach to tune the linewidth of random lasers for further applications in high-illumination imaging and biology detection., Comment: 19 pages,6 figures

Using polarization charges created at the metal-cadmium sulfide interface under strain to gate/modulate electrical transport and optoelectronic processes of charge carriers, the piezo-phototronic effect is applied to process mechanical and optical stimuli into electronic controlling signals. The cascade nanowire networks are demonstrated for achieving logic gates, binary computations, and gated D latches to store information carried by these stimuli.

As a key element in optical systems, a broadband and omnidirectional polarization beam splitter has been long desired. Here, based on anisotropic metamaterials, a perfect polarizing beam splitter is theoretically designed for the extremely broad frequency and angle bands without energy loss. When an electromagnetic wave is incident on the beam splitter, the transverse magnetic-polarized component suffers total reflection, while the transverse electric-polarized component is completely transmitted within the incident angle range [-90°, 90°] for the white light. This study provides a new approach to design an efficient polarizing beam splitter and may promote the development and applications of anisotropic metamaterials.

On the basis of cascade energy transfer between different dye molecules, single-excitation and low threshold coherent random lasing with a high quality factor ( similar to 13 000) over the whole visible range is experimentally observed using gold-silver bimetallic porous nanowires with abundant nanogaps as the scatterers. These nanogaps with different sizes in the bimetallic nanowires can produce continuous plasmonic resonance spectra and provide strong feedback or gain channels for the stimulated emission from different dye molecules. It guarantees a low threshold of lasing. Moreover, multi gain media can provide broad tunability of the emission wavelength when the system is pumped by single-wavelength pulses. It provides excellent flexibility for the design of multicolor output devices.

The defect mode in silver-doped photonic crystals is investigated. 1D and 3D photonic crystals were made by holography using dichromated gelatin mixed with silver nitrate. By controlling the concentration of the silver nitrate, the defect mode was observed in the bandgaps of the holographic photonic crystals. The numerical simulations were made, and the results showed the consistency with the experimental observations.

Different emission properties of band edge laser in a face centered cubic (FCC) photonic crystal pumped by ps and ns pulse were investigated experimentally. For the case pumped by ps laser, multi-mode emission is obtained and every modes have narrow line width. For the case pumped by ns laser, there is only a single dominant mode with high output intensity and a line width about several nanometers. Also, the lasing threshold pumped by ns laser is much lower than that pumped by ps laser, and the emission mode pumped by ns laser is more stable than that pumped by ps laser.

A 2-dimensional gradual period photonic heterostructure was made with holography by use of non-uniform swelling effect of dichromated gelatin during processing. In this structure, the symmetric point group of triangle lattice was debased to C2V from C6V. Theoretical analysis and experimental results show that omnidirectional band gap in visible range can be achieved with this kind of heterostructure made by low refractive index materials.

Methods of detecting a perfect invisible cloak are analyzed. A classical frequency-domain method of detection is proposed. It is based on the detection of the difference between the nonlinear responses of the materials of the cloak and the background. The cloak treated here is perfect working within any frequency. The method for detecting the cloak in the frequency domain is demonstrated numerically for an example.

Analytical solution of band gaps in two-dimensional (2-D) photonic crystals made by multi-beam interference was put forward. This solution gives concise analytical expression of every band gap. The quantitative relationship between the characters of band gaps and parameters of the materials of 2-D PC is different from that of one-dimensional (1-D) PC. For structures satisfying some conditions, the properties of band gaps obtained by the analytical solution are in good consistency with that obtained by the numerical simulations using plane wave expansion method. It showed why both TE and TM waves should have the same band structure in certain direction of 2-D PC with low refractive index. Also, it should be noted that the presented approach is accurate only for low index structures.

Enhanced transmission peaks can be obtained in a dielectric photonic crystal with metal film defect. These peaks occur only in the band gaps, and their heights decrease sharply when they deviate from the band gaps. Theoretical analysis shows that, since the metal film defect mode possesses very high density of mode, high transmission of light in particular band can be achieved even by a metal “block” while high absorption of the light in other bands still exists. The physical mechanism of this phenomenon is essentially different from the resonant tunneling effect of layered metallic films. Since metal has high reflection and strong absorption of the light wave without being enhanced, so, basing on this mechanism, a narrow bandwidth filter with high transmission in UV range and suppression in while the visible, infrared, and even microwave range can be achieved.

Simultaneous excitation of cavity resonance (CR) and surface plasmon resonance (SPR) was observed in the angular spectrum by substituting Ag/Al2O3/Ag layers for the metal film in a Kretschmann structure. Two reflective valleys, elicited respectively by CR and SPR, appeared at different positions in the angular spectrum. The former is the sum of enhanced transmission of CR and absorption of the metal, expressed in the reflection spectrum and extremely insensitive to the changes of the surface environment (refractive index). The latter behavior is like that when two metal films are stuck together: it has almost the same resonance depth and width, and is extremely sensitive to the changes of the surface environment. Moreover, two SPR peaks could be excited simultaneously at one angle but with different wavelengths in the frequency spectrum, which is not seen in traditional Kretschmann structures.