Photocatalytic removal of heavy metal ions and antibiotics in agricultural wastewater:A review

In recent years,the treatment of agricultural wastewater has been an important aspect of environmental protection.The purpose of photocatalytic technology is to degrade pollutants by utilizing solar light energy to stimulate the migration of photocarriers to the surface of photocatalysts and occur reduction-oxidation reaction with pollutants in agricultural wastewater.Photocatalytic technology has the characteristics of high efficiency,sustainability,low-energy and free secondary pollution.It is an environmental and economical method to recover water quality that only needs sunlight.In this paper,the mechanism and research progress of photocatalytic removal of heavy metal ions and antibiotics from agricultural water pollution were reviewed by combining photocatalytic degradation process with agricultural treatment technology.The mechanism of influencing factors of photocatalytic degradation efficiency was discussed in detail and corresponding strategies were proposed,which has certain reference value for the development of photocatalytic degradation.

High-power linearly-polarized tunable Raman fiber laser

In this study, we demonstrate an all-fiber high-power linearly-polarized tunable Raman fiber laser system. An in- house high-power tunable fiber laser was employed as the pump source. A fiber loop mirror （FLM） serving as a high reflectivity mirror and a flat-cut endface serving as an output coupler were adopted to provide broadband feedback. A piece of 59-m commercial passive fiber was used as the Raman gain medium. The Raman laser had a 27.6 nm tuning range from 1112 nm to 1139.6 nm and a maximum output power of 125.3 W, which corresponds to a conversion efficiency of 79.4%. The polarization extinction ratio （PER） at all operational wavelengths was measured to be over 21 dB. To the best of our knowledge, this is the first report on a hundred-watt level linearly-polarized tunable Raman fiber laser.

Revisiting the single-step synthesis of quantum dots:The hidden ligand-promoted surface reaction channels

In this work,we revisited the single-step synthesis of CdE(E=S,Se,and Te)quantum dots(QDs).Powdered CdO and elemental chalcogen were directly used for heating-up synthesis.Firstly,the in situ dissolution of the solid precursors and related QD formation channels were preliminarily investigated.In general,QDs were generated from homogeneous reactions between dissolved cadmium and chalcogen precursors in bulk solution.We found that,during single-step synthesis,both the dissolution of CdO and selenium proceeded faster than their ex situ dissolution respectively.To explain this result,we proposed the existence of extra surface reaction channels for QD formation.That is,QDs could also be generated via on-surface reactions between the solid precursors and the dissolved counter precursors(as“ligands”).The happening of these extra surface reactions would increase the overall dissolution rate of CdO and selenium.Further,the circulation of oleic acid which is peculiar to such single-step synthesis should also partly account for the accelerated dissolution of CdO.Finally,by comparing with two-step synthesis using pre-dissolved CdO,we presented that such single-step synthesis was reliable in making uniform CdE QDs with good reproducibility.Our work reaffirmed the great potential of this single-step strategy in cost-effective synthesis of monodisperse QDs.Moreover,the ligand-promoted surface reaction channels would be applicable in solution-phase synthesis of metal chalcogenide nanocrystals from solid precursors.

Six kilowatt record all-fiberized and narrow-linewidth fiber amplifier with near-diffraction-limited beam quality

In this work,an all-fiberized and narrow-linewidth fiber amplifier with record output power and near-diffraction-limited beam quality is presented.Up to 6.12 kW fiber laser with the conversion efficiency of approximately 78.8%is achieved through the fiber amplifier based on a conventional step-index active fiber.At the maximum output power,the 3 dB spectral linewidth is approximately 0.86 nm and the beam quality factor is M_(x)^(2)=1.43,M_(y)^(2)=1.36.We have also measured and compared the output properties of the fiber amplifier employing different pumping schemes.Notably,the practical power limit of the fiber amplifier could be estimated through the maximum output powers of the fiber amplifier employing unidirectional pumping schemes.Overall,this work could provide a good reference for the optimal design and potential exploration of high-power narrow-linewidth fiber laser systems.

Pump scheme optimization of an incoherently pumped high-power random fiber laser

Optical signal-to-noise ratio(OSNR) is one of the most significant parameters for the performance characterization of random fiber lasers(RFLs) and their application potentiality in sensing and telecommunication. An effective way to improve the OSNR of RFLs is pump scheme optimization, for example, employing a temporally stable source as the pump. In this paper, the output performance of an incoherently pumped RFL dependence on the pump bandwidth has been investigated both in experiment and theory. It is found that a high-OSNR RFL can be achieved with broadband amplified spontaneous emission(ASE) source pumping, and a relatively broad pump bandwidth can also help suppress the spectral broadening while maintaining an ultra-high spectral purity.By optimizing the pump bandwidth to ~10 nm, maximum OSNR of ~39 dB(corresponding to a spectral purity of ~99.96%) with more than 99 W output power can be obtained. Moreover, for the pump bandwidth of 0.6–40 nm, the spectral purity can reach as high as >99% with the pump power ranging from ~85 to ~117 W.In addition, with the aid of theoretical simulation based on a modified power balance model, we find that the increment of pump bandwidth can decrease the effective Raman gain coefficient, further influencing the gain characteristics, nonlinear effects, and eventually the output performance. This work provides new insight into the influence of the pump characteristics on the output performance of incoherently pumped RFLs.

High Power Linearly Polarized Raman Fiber Laser With Stable Temporal Output

We demonstrate a high power linearly polarized Raman fiber laser(RFL)pumped by an amplified spontaneous emission(ASE)source.Temporal-stable operation of RFL could be ensured owing to the employment of ASE,which mitigates the inherent intensity noise compared with the classic scheme adopting laser oscillator as pump source.In this experiment,the RFL has up to 119.5W output power,with central wavelength of 1129.2nm,and full width at half maximum(FWHM)linewidth of about 4.18nm.The polarization extinction ratio(PER)of the Raman laser is about 23dB.Moreover,this laser has excellent long-term and short-term stabilities in terms of the output power and time domain.

Optical rogue wave in random fiber laser

The famous demonstration of optical rogue waves(RWs),a powerful tool to reveal the fundamental physics in different laser scenarios,opened a flourishing time for temporal statistics.Random fiber laser(RFL)has likewise attracted wide attention due to its great potential in multidisciplinary demonstrations and promising applications.However,owing to the distinctive cavity-free structure,it is a scientific challenge to achieve temporal localized RWs in RFLs,whose feedback arises from multiple scattering in disordered medium.Here,we report the exploration of RW in the highly skewed,transient intensity of an incoherently pumped RFL for the first time,to our knowledge,and unfold the involved kinetics successfully.The corresponding frequency domain measurements demonstrate that the RW event arises from a crucial sustained stimulated Brillouin scattering process with intrinsic stochastic nature.This investigation highlights a novel path to fully understanding the complex physics,such as photon propagation and localization,in disordered media.

Ultralow-quantum-defect Raman laser based on the boson peak in phosphosilicate fiber

Quantum defects(QDs)have always been a key factor of the thermal effect in high-power fiber lasers.Much research on low-QD fiber lasers has been reported in the past decades,but most of it is based on active fibers.Besides,Raman fiber lasers based on the stimulated Raman scattering effect in passive fiber are also becoming an important kind of high-power fiber laser for their unique advantages,such as their significantly broader wavelength-tuning range and being free of photon darkening.In this paper,we demonstrate an ultralow-QD Raman fiber laser based on phosphosilicate fiber.There is a strong boson peak located at a frequency shift of 3.65 THz in the Raman gain spectrum of the phosphosilicate fiber we employed.By utilizing this boson peak to provide Raman gain and adopting an amplified spontaneous emission source at 1066 nm as the pump source,1080 nm Stokes light is generated,corresponding to a QD of 1.3%.The spectral purity at 1080 nm can be up to 96.03%,and the output power is 12.5 W,corresponding to a conversion efficiency of 67.2%.Moreover,by increasing the pump wavelength to 1072 nm,the QD is reduced to 0.74%,and the output power at 1080 nm is 10.7 W,with a spectral purity of 82.82%.To the best of our knowledge,this is the lowest QD ever reported for Raman fiber lasers.This work proposes a promising way of achieving high-power,high-efficiency Raman fiber lasers.

Effects of background spectral noise in the phase-modulated single-frequency seed laser on high-power narrow-linewidth fiber amplifiers

In this work,we analyze the effects of the background spectral noise in phase-modulated single-frequency seed lasers on the spectral purity of high-power narrow-linewidth fiber amplifiers.Through demonstrating the spectral evolution of the phase-modulated single-frequency part and the background spectral noise in a narrow-linewidth fiber amplifier,the mechanism for the spectral wing broadening effect is clarified and design strategies to maintain high spectral purity are given.Specifically,the background spectral noise in phase-modulated single-frequency seed lasers could lead to obvious spectral wing broadening and degeneration of spectral purity in narrow-linewidth fiber amplifiers through the four-wave-mixing effect.Notably,the spectral wing broadening effect could be suppressed by filtering out the background spectral noise in the seed laser or applying a counter-pumped configuration in the fiber amplifier.We have also conducted contrast experiments,which have verified the validity of the theoretical model and the design strategies for high-spectral-purity operation.

Hundred-watt-level linearly polarized tunable Raman random fiber laser

A high power linearly polarized tunable Raman random fiber laser（RFL） was studied theoretically and experimentally. The parameters required for the system design were obtained through numerical simulation, based on which a hundred-watt-level linearly polarized tunable RFL was successfully demonstrated. The central wavelength can be continuously tuned from 1113.76 to 1137.44 nm, and the output power exceeds 100 W for all of the lasing wavelengths with the polarization extinction ratio（PER） exceeding 20 d B at the maximum output power.Besides, the linewidth, spectral evolution, and temporal dynamics of a specified wavelength（1124.72 nm） were investigated in detail. Moreover, the theoretical results and the experimental results fit well. To the best of our knowledge, this is the first time for a hundred-watt-level linearly polarized tunable RFL ever reported.

Effects of background spectral noise in the phase-modulated single-frequency seed laser on high-power narrow-linewidth fiber amplifiers

In this work, we analyze the effects of the background spectral noise in phase-modulated single-frequency seed lasers on the spectral purity of high-power narrow-linewidth fiber amplifiers. Through demonstrating the spectral evolution of the phase-modulated single-frequency part and the background spectral noise in a narrow-linewidth fiber amplifier, the mechanism for the spectral wing broadening effect is clarified and design strategies to maintain high spectral purity are given. Specifically, the background spectral noise in phase-modulated single-frequency seed lasers could lead to obvious spectral wing broadening and degeneration of spectral purity in narrow-linewidth fiber amplifiers through the four-wave-mixing effect. Notably, the spectral wing broadening effect could be suppressed by filtering out the background spectral noise in the seed laser or applying a counter-pumped configuration in the fiber amplifier. We have also conducted contrast experiments, which have verified the validity of the theoretical model and the design strategies for high-spectral-purity operation.

Investigation on extreme frequency shift in silica fiber-based high-power Raman fiber laser

In this paper, we experimentally investigated the extreme frequency shift in high-power Raman fiber laser(RFL). The RFL was developed by using a pair of fiber Bragg gratings with fixed and matched central wavelength(1120 nm)combined with a piece of 31-m-long polarization maintaining(PM) passive fiber adopted as Raman gain medium.The pump source was a homemade high-power, linearly polarized(LP) wavelength-tunable master oscillator power amplifier(MOPA) source with ～25 nm tunable working range(1055–1080 nm). High-power and high-efficiency RFL with extreme frequency shift between the pump and Stokes light was explored. It is found that frequency shift located within 10.6 THz and 15.2 THz can ensure efficient Raman lasing, where the conversion efficiency is more than 95% of the maximal value, 71.3%. In addition, a maximum output power of 147.1 W was obtained with an optical efficiency of71.3%, which is the highest power ever reported in LP RFLs to the best of our knowledge.