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Abstract: Solitons can form bound states that are frequently referred to as soliton molecules as they exhibit molecule‐like dynamics. The build‐up phase of the optical soliton molecule remains elusive. Here, by means of a time‐stretch technique that enables real‐time access to the spectral and temporal dynamics, rich nonlinear processes involved in the build‐up of soliton molecules are revealed in an ultrafast fibre laser. Specifically, the formation of closely‐ and well‐separated bound solitons are resolved. In both cases, the build‐up phases consist of three nonlinear stages including mode locking, soliton splitting, and soliton interactions. For closely‐separated bound solitons, soliton interactions display wide diversities in repeated measurements, including soliton attraction, repelling, collision, vibration, and annihilation. For well‐separated bound solitons, repulsive interactions dominate the soliton interactions. Numerical simulations corroborate these experimental observations. Furthermore, a conceptually different soliton molecule, the intermittent‐vibration soliton molecule, is discovered and characterized. It is the intermediate state between the vibrational and stationary soliton molecules. The author's findings could assist in the understanding of the build‐up phase of localized structures in different dissipative systems. [ABSTRACT FROM AUTHOR]

Strong broadband white photoluminescence was observed in fullerene-doped phosphate and fluorophosphate optical glasses irradiated by an ultraviolet laser. Microphotoluminescence measurements demonstrated the existence of microislands in those amorphous glasses, where fullerene dopants provided high photosensitivity and optical nonlinearity. Nonlinear photoluminescence was observed under ultralow continuous-wave laser excitations. The photoluminescence peak wavelengths were demonstrated to depend nonlinearly on the laser excitation power. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In recent years, the fields of nanophotonics and nano-optics have been greatly fueled by rapid advancements in photonic science and technology, especially by the emergence of novel optical nanomaterials and new functional nanostructures. The above articles in this Special Issue present some of the challenges and opportunities in the field of nanophotonics and nanomaterials, which are expected to have a broad impact on a variety of applications in areas of scientific, industrial, and societal significance. 35269228 8 Zhao M., Yu J., Fu L., Guan Y., Tang H., Li L., Cheng J. Thin-Film Solar Cells Based on Selenized CuSbS2 Absorber. [Extracted from the article]

To make the best and highest use of broad spectrum solar energy remains a tremendous challenge and the main target in the photocatalytic area. A novel promising photocatalyst supported on surface plasmon resonance of Ag nanoparticles (NPs) and upconversion photoluminescence property from carbon quantum dots (CQDs) is reported to improve broad spectrum absorption and photoinduced charge transfer of graphitic carbon nitride (g-C 3 N 4 ) in the photo-driven H 2 production for the first time. Here the new-styled nanocomposites not only have more prominent UV–vis photocatalytic ability, also can harness near-infrared light to trigger hydrogen evolution in aqueous solution. Meanwhile, Ag NPs and CQDs serve as electron-reservoirs, which stimulate the separation of photo-generated electron-holes, enhancing quantum efficiency of g-C 3 N 4 . Remarkably, the most notable photocatalytic hydrogen generation as high as 626.93 μmol g −1 h −1 under visible light, which is about 6.7 and 2.8 times higher than pure g-C 3 N 4 and the best CQDs/g-C 3 N 4 composite respectively, was achieved upon 6 mL CQDs/g-C 3 N 4 (6CCN) loaded with 3 wt% Ag. Moreover, a facile method is designed to prepare Ag/CQDs/g-C 3 N 4 photocatalysts, and their chemical composition, morphologies, optical properties and stability were characterized methodically. [ABSTRACT FROM AUTHOR]

Triphenylamine functionalized bithiazole-cobalt complex ( Co-2TPABTz ) sensitized by Ag nanoparticles (NPs) exhibit highly efficient photocatalytic hydrogen generation. The resulting composite 3 showed excellent photocatalytic activity (20.65 mmol h −1 g −1 ) under visible light illumination, and maintained outstanding long-term stability after eight-cycle tests (32 h) as well. [ABSTRACT FROM AUTHOR]

Two novel spirobifluorene-diarylethenes compounds with furan ( 9a) and thiophen ( 8a) as heterocyclic aryl groups were successfully synthesized, and their structures were fully characterized with FTIR, NMR, mass spectra (MS), and elemental analysis. Their photochromic properties were examined. The results indicated that they showed good photochromic behaviors in hexane and acetonitrile. The fluorescence emission was quenched along with the photochromism from open ring to closed ring. Large fluorescence emission blue-shift was clearly observed in polar solvents. Furthermore, the of 8a and 9a was greatly improved by introducing spirobifluorene group into the molecules. The 5% loss weight temperature of 9a was 59°C higher than that of 10a without spirobifluorene. [ABSTRACT FROM AUTHOR]

In this work plasmon propagation and highly sensitive hydrogen sensing are demonstrated in single‐crystal Pd and its alloy nanowires, based on an evanescent wave coupling technique using optical fiber tapers. The plasmon propagation losses of Pd nanowires on an MgF2 substrate are measured to be ∼2 dB/μm (at 635 nm). Using a suspension scheme of the nanowire, the propagation losses decrease to ∼0.6 dB/μm in air. Utilizing an alloying technique, single‐crystal PdAg nanowires are fabricated and exhibit decreasing and tunable propagation losses. Furthermore, Pd nanowires are used for plasmonic gas sensing with amplitude sensitivity of ∼11 dB to 3.6% hydrogen gas, which is much higher than those in photonic nanowire sensors. The concentration detection limit is about 0.2%, which is lower than those in photonic nanowire sensors and most surface plasmon resonance sensors. The hysteresis effect of the Pd nanowire in hydrogen sensing is suppressed by using single‐crystal PdAu alloy nanowires. This work may find widespread application, ranging from sensing and integrated circuits to materials research. [ABSTRACT FROM AUTHOR]

Abstract: 2-(Dimesitylboryl)-9-ethyl-9H-carbazole (CzB), 2-(4-(dimesitylboryl)phenyl)-9-ethyl-9H-carbazole (CzPhB), 2-(5-(dimesityl-boryl)thiophen-2-yl)-9-ethyl-9H-carbazole (CzThB), and (E)-2-(4-(dimesitylboryl)styryl)-9-ethyl-9H-carbazole (CzSB) have been studied by theoretical measurements with GAUSSIAN software. To reveal the relationship between the structures and properties of these multifunctional electroluminescent materials, their geometrical structures of ground and excited-states were optimized by B3LYP/6-31G(d), HF/6-31G(d), and CIS/6-31G(d) methods, respectively. The lowest excitation energies (E g) and the maximum absorption and emission wavelengths of these compounds were calculated by time-dependent density functional theory methods. The important parameters for luminescent materials were also predicated including the reorganization energies, the ionization potentials and electron affinities. As a result of calculations, these molecules are considered as candidates for excellent OLEDs with good charge-transfer abilities, high blue-light emission and low energy barriers for charge injection, and the phene-based molecule has higher electron mobility and better equilibrium properties as compared to the other compounds. [Copyright &y& Elsevier]

Abstract: Mn2+-doped Ba2ZnS3 phosphors for white light emitting diodes (LEDs) have been prepared by high temperature solid-state reaction and their photoluminescence properties are reported. Diffuse reflection spectra of Ba2ZnS3 host and synthesized phosphors have been measured. The excitation spectrum extends a broad range of wavelength and is consistent with the diffuse reflectance spectra. The emission bands are due to 4T1(4G)→ 6A1(6S) transition of the Mn2+ ion and there exists efficient energy transfer from host to Mn2+ ions. The dependence of emission wavelength on Mn2+ concentration is studied. The decay curve of Mn2+ ions luminescence in Ba2Zn0.995S3:0.005 Mn2+ is also measured. [Copyright &y& Elsevier]

The Raman spectroscopy of purified chlorophyll (Chl) d extracted from Acaryochloris marina has been measured over the wide region of 250–3200 cm−1 at 77 K following excitation of its Soret band at 488 nm and analyzed with the aid of hybrid density-functional vibrational analyses. A Raman peak specific to Chl d, which arises from the formyl group 31 C&z.dbnd6;O stretching, was clearly observed at 1659 cm−1 with medium intensity. Peaks due to other C&z.dbnd6;O stretching vibrations of the 131 keto-, 133 ester- and 173 groups were also observed. Four very strong peaks were observed in the range of 1000–1600 cm−1, assigned to the CC stretching and mixtures of the CH3 bend and CN stretching. CCC and NCC bending contribute to medium intensity peaks at 986 and 915 cm−1. Out-of-plane CH bending at Chl d methine sites 10, 5 and 20 contribute to observed peaks at 885, 864 and 853 cm−1, respectively. A few modes involving the MgN stretching and MgNC bending motions were observed in the very low frequency range. Density functional theory (DFT) calculations have been used to make assignments on the observed Raman spectrum and the DFT results have been found to be in good agreement with the experimental results. [Copyright &y& Elsevier]

Sensitive mid‐infrared (MIR) spectroscopy is highly demanded in various fields ranging from industrial inspection, biomedical diagnosis to astronomical observation. However, the detection sensitivity of conventional MIR spectrometers is severely limited by excessive noises for existing infrared sensors, which hinders widespread use in photon‐scarce scenarios. Here, a broadband MIR single‐photon time‐stretch spectrometer is devised and implemented based on high‐fidelity spectral upconversion and time‐correlated coincidence counting. Specifically, a nanophotonic supercontinuum illumination covering 2.4–4.2 µm is nonlinearly converted to the near‐infrared band, where low‐loss single‐mode fiber and high‐performance silicon detector can be leveraged to facilitate dispersive operation and sensitive detection, respectively. The arrival time for the dispersed upconversion photons is precisely registered with a low‐timing‐jitter photon counter, which enables us to obtain a high spectral resolution about 0.5 cm−1 under a low‐light‐level illumination down to 0.14 photons/nm/pulse. In comparison to previous MIR upconversion spectrometers, the presented time‐stretch architecture favors single‐pixel simplicity and high‐throughput acquisition for the single‐photon spectral measurement. The achieved MIR spectroscopic features of broadband spectral coverage, sub‐wavenumber resolution, single‐photon sensitivity, and room‐temperature operation would stimulate immediate applications in material and life sciences. [ABSTRACT FROM AUTHOR]

We introduce a single-photon Sagnac interferometer for quantum cryptography using time-division phase modulation. The interferometer was arranged to allow coherent laser pulses to travel clockwise and counter-clockwise along the same fiber loop with the corresponding phases modulated in separated periods, interfering at the exit coupler. High visibility of the single-photon interference was observed over a long-distance Sagnac loop. Stable performance was realized by passive compensation of stress and temperature-dependent drifts of the fiber-optic path. Time-division phase encoding and decoding can be realized by controlling the applied electric pulses on integrated phase modulators in the Sagnac loop, which makes this system suitable for a practical quantum cryptography system. [ABSTRACT FROM AUTHOR]

The Raman spectroscopy of chlorophyll (Chl) d isolated from Acaryochloris marina has been measured in the range of 250–3200 cm−1 at 77 K following excitation of its Bx band at 488 nm. A peak at 1659 cm−1 of medium intensity arising from C&z.dbnd;O stretching vibration in the formyl group 31 specific to Chl d was observed clearly. Peaks due to other C&z.dbnd;O stretching vibrations of the 131 keto-, 133 ester- and 173 groups have also been observed with much weaker intensities. Intense Raman peaks in the range of 1000–1800 cm−1 are reported and homologous comparison with corresponding Raman shifts of Chl a, Chl b and BChl a are presented. [Copyright &y& Elsevier]

The appropriate amount of fullerene doping in phosphate and fluorophosphate optical glasses modifies the structures of glass matrices by bonding the nearby -[PO[sub 4]]- tetrahedra with nonbridging oxygen anions, and consequently building up observable conductivity at room temperature. Non-Arrhenius ionic conductivity is observed, which is interpreted as a result of the temperature dependence of the activation energies of the mobile cations. The variation of microphotoluminescence induced by the electric field presents us with an indirect way to characterize the random activation, percolation migration, and retrap of metal cations near fullerene-related amorphous islands. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

This study utilized a hydrothermal method to synthesize various metal‐modified rod‐like ceria catalysts (Fe, Co, Cu, Ni, La), achieving efficient COS removal at low temperatures. The research identified surface oxygen vacancies and basic sites as critical factors that influence the catalytic performance of COS hydrolysis. The addition of different metals to pristine ceria rods increased the specific surface area, oxygen vacancy content (Ov), and basicity, which enhanced the catalysts′ sulfur resistance and stability. Among all the catalysts tested, 10La‐CeO2 demonstrated the highest COS removal rate. This is because La doping significantly augmented Ov, providing more H2O adsorption and activation sites. Furthermore, 10La‐CeO2 showed enhanced Lewis basicity, making it easier for COS to adsorb and promote hydrolysis. The in situ DRIFTS results confirmed that appropriate oxygen vacancies and basic sites favored the formation of intermediates such as HCO3− and HSCO2−, promoting the decomposition of COS into H2S and CO2. [ABSTRACT FROM AUTHOR]

Extreme wave events or rogue waves (RWs) are both statistically rare and of exceptionally large amplitude. They are observed in many complex systems ranging from oceanic and optical environments to financial models and Bose–Einstein condensates. As they appear from nowhere and disappear without a trace, their emergence is unpredictable and non‐repetitive, which makes them particularly challenging to control. Here, the use of genetic algorithms (GAs), which are exclusively designed for searching and optimizing stationary or repetitive processes in nonlinear optical systems, is extended to the active control of extreme events in a fiber laser cavity. Feeding real‐time spectral measurements into a GA controlling the electronics to optimize the cavity parameters, the wave events are able to be triggered in the cavity that have the typical statistics of RWs in the frequency domain. The intensity of the induced RWs can also be tailored. This accurate control enables the generation of optical RWs with a spectral peak intensity 32.8 times higher than the significant intensity threshold. A rationale is proposed and confirmed by numerical simulations of the laser model for the related frequency up‐ and downshifting of the optical spectrum that are experimentally observed. [ABSTRACT FROM AUTHOR]

Nonlinear interaction of two or three synchronized coplanar filaments was demonstrated to generate plasma gratings with high electron density capable of effectively exciting samples. This excitation was further enhanced by multi-photoionization and electron collision. Consequently, an increase in laser pulse energy led to a decrease in the full width at half maxima (FWHM) of spectral lines, primarily observed in breakdown spectroscopic lines due to electron signal enhancement. Moreover, by measuring the emission line intensity as a function of time delay and excitation laser pulse energy, the radiative lifetime and self-absorption correlation coefficient of neutral atomic and ionic lines were determined to exhibit longed plasma lifetimes in the presence of filament interaction. The enhancement was particularly notable when using three coplanar coupled filaments for excitation, as it resulted in a plasma lifetime increase of approximately 50–60 ns compared to that when using two filaments for atomic lines. These findings indicate that high-electron density in plasma gratings could improve the application of filament-induced breakdown spectroscopy by enhancing spectral resolution, radiative lifetime, and spectral reproducibility. [ABSTRACT FROM AUTHOR]

Soliton explosion refers to a striking nonlinear dynamics in dissipative systems. In this state, a dissipative soliton collapses but returns back to its original state afterwards. Yet, the origin of such exotic soliton dynamics remains elusive. Here it is revealed that soliton collision can induce soliton explosions in a mode-locked fibre laser, benefiting from synchronous measurements of the spatio-temporal intensity evolution and the real-time spectra evolution using dispersive Fourier transform. Up to seven nonlinear regimes are observed successively in the laser by increasing the pump power only, including single-pulse mode locking, standard soliton explosions, noise-like mode locking, stable double pulsing, soliton collision induced explosions, soliton molecules, and double-pulse noise-like mode locking. These experimental findings are conducive to understand complex soliton dynamics in many nonlinear dissipative systems. Soliton explosions are a nonlinear instability phenomenon in which a dissipative soliton experiences a sudden structural collapse, but can return back to its original shape despite the strong energy dissipation. The authors report the experimental observation of soliton explosions in a fibre laser, finding that the instability is triggered by the collision of double dissipative solitons. [ABSTRACT FROM AUTHOR]

Time‐stretch spectroscopy is a powerful tool for studying transient and nonrepetitive physical events. Its extension to the fundamental molecular fingerprint region is promising for chemical and biological research but encounters difficulties in mid‐infrared photodetection and strong attenuation of aqueous environments. Here, mid‐infrared time‐stretch spectroscopy via coincidently‐pumped nonlinear frequency conversion for efficient mid‐infrared generation and detection is demonstrated. Broadband (≈200 cm−1) mid‐infrared spectra at 77.5 Mspectra s−1 with high signal‐to‐noise ratio are recorded. The single‐shot signal‐to‐noise ratio (SNR) measured within 2 ns exceeds 200. The method reveals fast spectral dynamics in a laser‐induced liquid evaporation process with a temporal resolution of 12.9 ns. Furthermore, probing transient spectra during evaporation opens up a new opportunity for interrogating chemicals inside or behind a thick water layer. Integrating high speed, broad bandwidth, high SNR, and the potential for operating under an aqueous environment, this method will benefit many applications including molecular dynamics, chemical reactions, and biological diagnostics. [ABSTRACT FROM AUTHOR]

Bi, Ga, and Al codoped germanium glass was prepared and its optical properties were investigated by absorption, photoluminescence excitation (PLE), and photoluminescence spectra. Two active centers which occupy strong and weak crystal field environment are identified by using the PLE spectrum. The tunable and ultrabroadband luminescence properties are originated from electron transitions of these two active centers. Internal optical gain around 1300 and 1560 nm has been detected. The wavelength-dependent internal gains excited with 808 and 980 nm laser diodes show different characteristics, and the relative flat optical amplification can be realized by choosing 980 nm pumping. [ABSTRACT FROM AUTHOR]

Transparent Ni2+-doped MgO–Al2O3–TiO2–SiO2 glass ceramics were prepared, and the optical properties of Ni2+-doped glass ceramics were investigated. Broadband emission centered at 1320 nm was observed by 980 nm excitation. The longer wavelength luminescence compared with Ni2+-doped Li2O–Ga2O3–SiO2 glass ceramics is ascribed to the low crystal field hold by Ni2+ in MgO–Al2O3–TiO2–SiO2 glass ceramics. The change in optical signals at the telecommunication bands with or without 980 nm excitation was also measured when the seed beam passes through the bulk gain host. [ABSTRACT FROM AUTHOR]

Sensitive and fast mid‐infrared (MIR) spectroscopy is highly attractive in a variety of applications including astronomical observation, pharmaceutical synthesis, and environmental monitoring. However, the performance of conventional MIR spectrometers has long been hindered by the limited sensitivity of narrow‐bandgap detectors and/or the deficient brightness of broadband light sources. Here, an ultra‐sensitive and broadband MIR upconversion spectrometer, which integrates a supercontinuum source covering 1.5–4.2 μ$\umu$m based on a silicon nitride nanophotonic waveguide, is devised and integrated. High‐efficiency and low‐noise nonlinear frequency upconversion is realized based on coincidence pulsed pumping with spectro‐temporal optimization, which enables leverage of silicon detectors for facilitating MIR single‐photon spectroscopy at 0.2 photons/nm/pulse. Furthermore, the upconversion‐based array spectrometer is manifested with high‐speed spectral acquisition rates beyond 200 kHz, which is about tenfold faster than the state‐of‐the‐art scan rates for FTIR‐based spectrometers at a comparable spectral resolution. The achieved features of broadband spectral coverage, single‐photon sensitivity, and sub‐MHz refreshing rate might open up new possibilities for infrared transient spectral measurements in combustion analysis, high‐throughput sorting, and reaction tracking, among others. [ABSTRACT FROM AUTHOR]

Stable propagation of laser filamentation arrays paves new ways for cross‐scale manufacturing. Although a single filament or multiple filaments can be used for laser processing in transparent media, sustainable developments of higher throughput and lower energy consumption are always the pursuit. Here, a proof‐of‐concept approach is proposed in which cross‐scale manufacturing of 3D microstructures is realized via an ionization‐induced volume plasma grating. The volume plasma grating is generated by the noncollinear interaction of two batches of arrays of multiple filaments. The volume plasma grating cannot only regulate the distribution of multiple filamentation but also promote the intensity inside the filaments. By this approach, 3D microstructures are written by 1D sample translation. In addition, rapid fabrications of volume gratings and terahertz wire grid polarizers (THz WGPs) are demonstrated by laser modification using volume plasma grating. The characteristics of the fabricated THz WGPs are comparable to those of commercial ones. The limitations and future implementations of this approach are discussed. [ABSTRACT FROM AUTHOR]

The perylene diimide substituented by thiophene rings at bay area shows photoactivity and can be used as a photo sensor, but another one substituented by mestylene groups is photostable. The single crystal of 1,7-mesitylene perylene diimide was obtained. X-ray diffraction data of the crystal revealed that the plane of the perylene core was hardly twisted by introduction of mesitylene groups. These mestylene groups are like clips maintaining the planarity of the perylene core. Density functional theory calculation was applied to study the difference of photophysical and photochemical properties. The discovery is valuable for design guidance of perylene diimides. [ABSTRACT FROM AUTHOR]

Photocatalytic hydrogen generation is a considerable promising technology to decrease climate change effect of CO 2 and to solve the increasing global demand for clean energy. Hydrogen generation driven by visible light still faces many challenges although great efforts have been made. Efficient charge separation plays an important role in solar-energy conversion by heterojunction photocatalysts. Herein we report that nickel ferrites covered by gold plasmonics form well-defined plasmonic photocatalysts for fluorescein-sensitized hydrogen production under visible-light irradiation with largely enhanced photoactivity due to fast separation of photogenerated electron-hole pairs. The optimal Au/NiFe 2 O 4 plasmonic photocatalysts with AuNP loading of 1.5 wt% shows the hydrogen production rate of 0.256 mmol g −1 h −1 via localized surface plasmon resonance effect of AuNPs. Fluorescein was acted as photosensitizer to extend the visible-light absorption of Au/NiFe 2 O 4 plasmonic photocatalysts and enhance photocatalytic hydrogen generation efficiency under visible-light irradiation. The optimum rate for hydrogen generation reached 3.162 mmol g −1 h −1 and the rate is about 60-fold and 12-fold higher than that of pure NiFe 2 O 4 and 1.5 wt% Au/NiFe 2 O 4 plasmonic photocatalysts, respectively. [ABSTRACT FROM AUTHOR]

Bare nanoparticles synthesized by laser ablation in water have found their application in catalysis, spectroscopy and biomedical research fields. In this perspective, how to efficiently produce stable nanoparticles with controllable size is an important topic and has attracted a lot of interests. Here, we introduce a multiple-pulse laser as the ablation source. By changing the number of sub-pulses, the average size of nanoparticles can be tuned in a broad range from ∼120 nm to ∼4 nm. The demonstration in this article may offer a new approach to fabricate ultrafine nanostructures and also help the scientific study of the mechanism in laser ablation. [ABSTRACT FROM AUTHOR]

Cu-Cu 2 O nanoparticles (NPs) decorated porous graphitic carbon nitride (g-C 3 N 4 ) (Cu-Cu 2 O/g-C 3 N 4 ) photocatalysts were prepared. When investment of copper source materials in the experiment increased to 7 wt%, the highest H 2 evolution rate (400 μmol g −1 h −1 ) was obtained under visible light irradiation in triethanolamine solution. This is about triple of pure g-C 3 N 4 (140 μmol g −1 h −1 ). Moreover, various amount of Erythrosin B dye was added into Cu-Cu 2 O/g-C 3 N 4 photoreaction solution and a significant enhancement of H 2 production rate was achieved. The highest H 2 production rate was 5000 μmol g −1 h −1 with 5 mg Erythrosin B in photoreaction system. Erythrosin B dye sensitized Cu-Cu 2 O/g-C 3 N 4 presented stable photocatalytic H 2 evolution ability and no noticeable degradation or change of photocatalyst were detected after six recycles. A possible photocatalytic mechanism of Erythrosin B dye sensitized Cu-Cu 2 O/g-C 3 N 4 for the enhancement of photocatalytic H 2 evolution is proposed. [ABSTRACT FROM AUTHOR]

We propose and implement a terahertz time-of-flight ranging system based on adaptive clock asynchronous optical sampling, where the timing jitter is corrected in real time to recover the depth information in the acquired interferograms after compensating for laser instabilities using electronic signal processing. Consequently, the involved measurement uncertainties caused by the timing jitter during the terahertz sampling process and the noise intensity of the terahertz electric field have been reduced by the utilization of the adaptive clock. The achieved uncertainty range is about 2.5 μm at a 5 cm distance after averaging the acquisition time of 1876 ms 5000 times, showing a significant improvement compared with the asynchronous optical sampling using a constant clock. The implemented terahertz ranging system only uses free-running mode-locked lasers without any phase-locked electronics, and this favors simple and robust operations for subsequent applications that extend beyond the laboratory conditions. [ABSTRACT FROM AUTHOR]

Determining how to improve the non-uniformity of arrayed waveguide grating (AWG) is of great significance for dense wavelength division multiplexing (DWDM) systems. In this work, a silicon nanowire-assisted AWG structure is proposed, which can achieve high uniformity with a low insertion loss. The article compares the effect of nanowire number and shape on uniformity and insertion loss, finding that double nanowires provide the best performance. Double nanowires with a width of 230 nm and length of 3.5 μm can consist of a slot configuration between arrayed waveguides, both connecting to the star coupler and spacing 165 nm from the waveguides. Compared with conventional 8- and 16-channel AWGs with channel spacing of 200 GHz, the non-uniformity of the presented structure can be improved from 1.09 and 1.6 dB to 0.24 and 0.63 dB, respectively. The overall footprint of the device would remain identical, which is 276 × 299 or 258 × 303 μm2 for the 8- or 16-channel AWG. The present high uniformity design is simple and easy to fabricate without any additional insertion loss, which is expected to be widely applied in the highly integrated DWDM systems. [ABSTRACT FROM AUTHOR]

A simple and convenient way to syn­thesize CuNPs in situ for photocatalytic hydrogen evolution is reported. The average rate of hydrogen evolution is 35 mmol g–1 h–1, and it can be recycled for further use with persistent photocatalytic efficiency in a stable and easy‐to‐­operate system. [ABSTRACT FROM AUTHOR]

In this study, a tunable gourd-shaped ring resonator is demonstrated to generate optical bistability. The system consists of two sub-rings for a gourd shape configuration with a U-shaped wave guiding pathway. The transfer matrix method and FDTD simulation are used to acquire the spectral characteristics of the system. For the fabricated device, the spectra profile and extinction ratio can be effectively tuned by the microheater above the U-shaped waveguide, which matches with the theoretical results. Due to the gourd structure of the resonator, the light waves in two rings can be cross-coupled with each other, and the optical bistability could come out effectively with the change in the input optical power around 6 mW. The presented optical bistability devices have great application potential in optical information processing such as optical storage, switch and logic operation. [ABSTRACT FROM AUTHOR]

Laser terahertz (THz) emission spectroscopy has broken the diffraction limit of THz frequencies and offers multifaceted spectroscopic and imaging capabilities for understanding the light–matter interaction in various quantum and energy materials. However, this advanced technique has not yet been applied in the recently extensively studied spintronic THz emission process, in which the material surface morphology may play an important role. Here, we conduct THz emission microscopy on 5.4-nm thick Pt/CoFeB/W heterostructures and obtain twice enhanced THz by tightly focusing the pumping laser, delicately choosing the radiation location on nanofilms and coating gold nanorods. Through THz emission mapping, the material surface morphology and its modification have a strong correlation with THz emission performance from spintronic emitters. Our proposed femtosecond fiber laser driven spintronic THz emission microscopy can provide exciting possibilities for studying surface morphology sensitive THz emission materials and microdomain ultrafast dynamics for low-dimensional small samples via further coupling optical microscopy. [ABSTRACT FROM AUTHOR]

Surface-enhanced Raman scattering (SERS) technology can amplify the Raman signal due to excited localized surface plasmon (LSP) from SERS substrates, and the properties of the substrate play a decisive role for SERS sensing. Several methods have been developed to improve the performance of the substrate by surface modification. Here, we reported a surface modification method to construct carbon-coated nanoporous gold (C@NPG) SERS substrate. With surface carbon-assistant, the SERS ability of nanoporous gold (NPG) seriously improved, and the detection limit of the dye molecule (crystal violet) can reach 10−13 M. Additionally, the existence of carbon can avoid the deformation of the adsorbed molecule caused by direct contact with the NPG. The method that was used to improve the SERS ability of the NPG can be expanded to other metal structures, which is a convenient way to approach a high-performance SERS substrate. [ABSTRACT FROM AUTHOR]

Hydrogenated crystalized TiO2−x with oxygen vacant (OV) doping has attracted considerable attraction, owing to its impressive photoactivity. However, amorphous TiO2, as a common allotrope of titania, is ignored as a hydrogenated templet. In this work, hydrogenated amorphous TiO2−x (HAm-TiO2−x) with engineered surface OV and high surface area (176.7 cm2 g−1) was first prepared using a unique liquid plasma hydrogenation strategy. In HAm-TiO2−x, we found that OV was energetically retained in the subsurface region; in particular, the subsurface OV-induced energy level preferred to remain under the conduction band (0.5 eV) to form a conduction band tail and deep trap states, resulting in a narrow bandgap (2.36 eV). With the benefits of abundant light absorption and efficient photocarrier transportation, HAm-TiO2−x coated glass has demonstrated superior visible-light-driven self-cleaning performances. To investigate its formaldehyde photodegradation under harsh indoor conditions, HAm-TiO2−x was used to decompose low-concentration formaldehyde (~0.6 ppm) with weak-visible light (λ = 600 nm, power density = 0.136 mW/cm2). Thus, HAm-TiO2−x achieved high quantum efficiency of 3 × 10−6 molecules/photon and photoactivity of 92.6%. The adsorption capabilities of O2 (−1.42 eV) and HCHO (−1.58 eV) in HAm-TiO2−x are both largely promoted in the presence of subsurface OV. The surface reaction pathway and formaldehyde decomposition mechanism over HAm-TiO2−x were finally clarified. This work opened a promising way to fabricate hydrogenated amorphous photocatalysts, which could contribute to visible-light-driven photocatalytic environmental applications. [ABSTRACT FROM AUTHOR]

Three new complexes of the wholly deprotonated flexible ligand m -phenylenediacrylate acid (H 2 mpda), namely, [Zn (mpda) (H 2 O)] [1] , [Pr 2 (mpda) 2 (H 2 O) 2 (CHOO) 2 ] [2] , and [Mn 2 (mpda) 2 (H 2 O) 4 ] [3] , were synthesized by the solvothermal reaction. The complexes were characterized by IR spectroscopy, thermogravimetric analysis, and X-ray single-crystal diffraction. A mixed sample [Nd(mpda)(H 2 O)(CHOO)·Pr(mpda)(H 2 O)(CHOO)] [2"] was also synthesized and studied. Compounds [1] and [2] exhibit a selective sensing function with respect to acetone, and they are a potential luminescent sensory material for the selective detection of Zn 2+ and Ni 2+ ions, respectively. Furthermore, the fluorescent changes of compound [1] upon the addition of cations (Fe 3+ and Zn 2+ , Bi 2+ and Zn 2+ ) are utilized to construct two logic gates at the molecular level. [ABSTRACT FROM AUTHOR]

A novel trivalent europium, Eu(III), 2,2′-bipyridine-5,5′-dicarboxylic acid (bpdc) metal-organic framework, namely, [Eu4(bpdc)6(CH3NH2)3(DMSO)(H2O)] 1 was synthesized by the solvothermal reaction of bpdc with trivalent Eu(III) salts in a mixed solvent system containing N,N′-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO). The single X-ray diffraction indicated that complex 1 had a novel porous three-dimensional framework with two different binuclear metal units. The photoluminescence spectrum of the complex displayed strong emission maxima at 472 and 618nm. [ABSTRACT FROM AUTHOR]

Plasma-grating-induced breakdown spectroscopy (GIBS) has proven itself superior to filament-induced breakdown spectroscopy (FIBS) in detection of trace elements in soil due to the higher intensity and electron density inside the plasma waveguide. The 2D plasma grating generated by the interference of three non-collinear and non-coplanar femtosecond filaments may become an ideal excitation source for ablation and hence we propose the technique multidimensional-plasma-grating-induced breakdown spectroscopy (MIBS). We demonstrate that MIBS is greatly affected by the laser polarization and inter-pulse delay. The signal intensity with MIBS is observed to be 2 times greater than that of GIBS and the induced plasma lifetime with MIBS has also increased by about 20%. Finally, we demonstrate that the limit of detection (LOD) is reduced from 394.40 ppm for GIBS to 306.47 ppm for MIBS, indicating that MIBS is a promising alternative in detecting trace elements. [ABSTRACT FROM AUTHOR]

Harnessing pulse generation from an ultrafast laser is a challenging task as reaching a specific mode‐locked regime generally involves adjusting multiple control parameters, in connection with a wide range of accessible pulse dynamics. Machine‐learning tools have recently shown promising for the design of smart lasers that can tune themselves to desired operating states. Yet, machine‐learning algorithms are mainly designed to target regimes of parameter‐invariant, stationary pulse generation, while the intelligent excitation of evolving pulse patterns in a laser remains largely unexplored. Breathing solitons exhibiting periodic oscillatory behavior, emerging as ubiquitous mode‐locked regime of ultrafast fiber lasers, are attracting considerable interest by virtue of their connection with a range of important nonlinear dynamics, such as exceptional points, and the Fermi‐Pasta‐Ulam paradox. Here, an evolutionary algorithm is implemented for the self‐optimization of the breather regime in a fiber laser mode‐locked through a four‐parameter nonlinear polarization evolution. Depending on the specifications of the merit function used for the optimization procedure, various breathing‐soliton states are obtained, including single breathers with controllable oscillation period and breathing ratio, and breather molecular complexes with a controllable number of elementary constituents. This work opens up a novel avenue for exploration and optimization of complex dynamics in nonlinear systems. [ABSTRACT FROM AUTHOR]

Two mixed-ligand coordination polymers (CPs) based on a biphenyl-based dicarboxylate ligand and 4,4′-bipyridine or imidazole co-ligand, namely, [Co(DMBDA)(bpy)] n ( 1) (H2DMBDA = 2,2′-dimethylbiphenyl-4,4′-dicarboxylic acid, bpy = 4,4′-bipyridine) and [Zn(DMBDA)(Im)] n ( 2) (Im = imidazole), were obtained under hydrothermal conditions. Compound 1 exhibits a new (4,6)-connected network with a {44 ·610 ·8}{44 ·62} Schläfli symbol, whereas compound 2 shows a 4-connected NbO-type topology. These coordination polymers represent two rare examples of CPs based on 2,2′-dimethylbiphenyl-4,4′-dicarboxylic acid. The solid-state luminescent behaviors of the novel CPs were also investigated at room temperature. [ABSTRACT FROM AUTHOR]

Fluorescence resonance energy transfers (FRET) between cyan fluorescent protein (CFP) and yellow fluorescent protein (YFP) on nanoporous gold (NPG) are systematically investigated by controlling the distance between NPG and fluorescent proteins with polyelectrolyte multilayers. The FRET between CFP and YFP is significantly enhanced by NPG, and the maximum enhancement is related to both ligament size of NPG and the distance between NPG and proteins. With the optimized distance, 18-fold FRET enhancement was obtained on NPG compared to that on glass, and the conversion efficiency is about 90%. The potential to tune the characteristic energy transfer distance has implications for applications in nanophotonic devices and provides a possible way to design sensors and light energy converters. [ABSTRACT FROM AUTHOR]

Abstract: Three novel triazine derivatives, (E)-4-(2-(4,6-dimethyl-1,3,5-triazin-2- yl)vinyl)- N,N-di-p-tolylaniline (a), 4,4′–((1E,1′E)-(6-methyl-1,3,5-triazine-2,4-diyl) bis(ethene-2,1-diyl))bis(N,N-di-p-tolylaniline) (b), and 4,4′,4′′–((1E,1′E,1′′E)-(1,3,5- triazine-2,4,6-triyl)tris(ethene-2,1-diyl))tris(N,N-di-p-tolylaniline) (c), were designed and synthesized. Their photophysical and photochemical properties were investigated systematically including single-photon absorption, nonlinear optical absorption (NOA) and up-converted fluorescence. Interestingly, the compound a with single branch showed pure three-photon absorption phenomenon, while the corresponding b and c indicated two-photon induced excited-state absorption properties, showing strong structure-dependence relationship. The results offer a method to design and synthesize organic molecules for multiphoton materials. It was noted that the three-photon cross-section value (δ3 ) of a was up to 1.35 × 10−76 cm6 s2. Correspondingly, the two-photon (δ2 ) and excited-state cross-section (δe ) values of b and c also were obtained, and value of them were 485 GM and 1.03 × 10−17 cm2 for b, and 1100 GM and 1.27 × 10−18 cm2 for c, respectively. [Copyright &y& Elsevier]

Abstract: Two new fullerene–fluorene dyads, N-methyl-2-(2-fluorenyl)-3,4-[60]fuller-pyrrolydine (1) and N-methyl-2-(2-fluorenyl)-3,4-[70]fullerpyrrolydine (2), were synthesized and their structures were confirmed by MALDI-MS, 1H NMR and FT-IR. Their electrochemical and optical properties were investigated by cyclic voltammetry and Z-scan technique, including, electronic potentials, two-photon absorption cross-sections (σ 2), nonlinear refractive indexes (n 2), microscopic second-order hyperpolarizabilities (γ R ) and third-order nonlinear susceptibilities ( and ). Importantly, the and σ 2 in 2 were increased above 35% due to [70]fullerene unit than that of 1. [Copyright &y& Elsevier]

Abstract: Four multifunctional 8-hydroxyquinoline derivatives were designed and synthesized, their structures were identified by FT-IR, 1H NMR, MS and elemental analysis. Among them are (E)-2-(2-(9-(4-methoxyphenyl)-9H-carbazol-3-yl)vinyl) quinolato-zinc (1), (E)-2-(2-(9-p-tolyl-9H-carbazol-3-yl)vinyl)quinolato-zinc (2), (E)-2-(2-(9H-fluoren-2-yl)vinyl)quinolato-zinc (3), and (E)-2-(2-(phenanthren-9-yl)vinyl)quinolato-zinc (4). The electroluminescence (EL) and hole-transporting characteristics of these materials were investigated on four configurations: (A) ITO/2-TNATA/NPB/1, 2, 3 or 4/Alq3/LiF/Al; (B) ITO/2-TNATA/NPB/1, 2, 3 or 4/LiF/Al; (C) ITO/2-TNATA/1, 2, 3 or 4/Alq3/LiF/Al; and (D) ITO/2-TNATA/1 or 2/NPB/Alq3/LiF/Al. The maximum luminescence and current efficiencies of are 3556cdm−2 (at 13V) and 2.17cdA−1 (at 9V) for compound 2, 4624cdm−2 (at 15V) and 2.1cdA−1 (at 7V) for compound 3, and 3164cdm−2 (at 14V) and 1.83cdA−1 (at 13V) for compound 4 in the configuration D, respectively, indicating that they are good multifunctional materials with strong hole-transporting abilities and luminescence properties. [Copyright &y& Elsevier]

We demonstrated passively Q-switched mode-locking in a laser-diode pumped c-cut Nd:GdVO4 laser with a Cr4+:YAG crystal as the intracavity saturable absorber. At a pump power of 17.3 W, the Q-switched envelope repetition rate was 37 kHz with the maximum average output power of 2.1 W, while the mode-locked pulses within the Q-switched envelope had a repetition rate of 143 MHz. Experimental comparison between c-cut and a-cut Nd:GdVO4 lasers indicated that the c-cut Nd:GdVO4 was more suitable for Q-switched mode-locking. [Copyright &y& Elsevier]

We experimentally compared pulsed lasers from off-axially cut and a-cut Nd:YVO4 crystals passively Q-switched by Cr4+:YAG crystals as the intracavity saturable absorbers. As compared to the a-cut Nd:YVO4 laser, the 45° off-axially cut Nd:YVO4 laser could be Q-switched passively to output much shorter pulse width with a lower repetition rate. Laser pulses from the off-axially cut crystal were stable in the output polarization states. [Copyright &y& Elsevier]

Edge enhanced imaging via the spiral phase contrast enables to reveal the phase or amplitude gradients of a target, which has been proved useful in feature recognition, machine vision, and object identification. A long quest is to extend the operation wavelength into the mid‐infrared (MIR) region, as highly demanded in various fields including infrared sensing, astronomic observation, and biomedical diagnosis. Here, ultra‐sensitive MIR imaging at the single‐photon level based on nonlinear frequency upconversion is demonstrated, where the spectrally converted replica of the MIR object image at 3070 nm is captured by a silicon electron multiplying charged coupled device. The imaging sensitivity is significantly improved by the coincidence pulsed pumping with a spectro‐temporal optimization. Furthermore, the edge enhancement is realized by imprinting the spiral phase pattern of the pump onto the upconverted field at the Fourier plane within the nonlinear crystal. Such a nonlinear spatial filter not only provides an effective way to implement the required high‐fidelity vortex screening in the edge enhanced detection, but also renders the MIR illumination into a visible image in an efficient and low‐noise fashion. The presented system for MIR edge enhanced imaging might facilitate immediate applications in label‐free histopathological diagnosis and non‐destructive defect inspection. [ABSTRACT FROM AUTHOR]

Reports on the introduction of a stable, long distance single-phase photon Sagnac interferometer. Compensation for phase drift caused by the change of the fiber optic path; Realization of the single-photon interference with the use of time-division phase modulation; Indication that the time-division phase-modulated Sagnac interferometer could lead to practical applicability of single-photon routing and quantum cryptography.