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.

血清降钙素原、白细胞介素、肿瘤坏死因子和全血超敏C-反应蛋白用于小儿细菌性肺炎检测的效果分析

目的探讨在小儿细菌性肺炎中检测血清降钙素原(procalcitonin,PCT)、白细胞介素(IL-6、IL-8)与肿瘤坏死因子(tumor necrosis factor-α,TNF-α)和全血超敏C-反应蛋白(hypersensitive C-reactive protein,hs-CRP)的临床效果。方法选取2015年6月-2016年6月我院检验科收治的细菌性肺炎患儿50例为观察组,选择同期于我院体检的健康儿童50例为对照组,检测并比较两组小儿的PCT、IL-6、IL-8、TNF-α与hs-CRP水平。结果观察组小儿的各项指标水平均明显高于对照组,差异均有统计学意义(P<0.05)。结论血清PCT、IL-6、IL-8、TNF-α与hs-CRP水平用于检测小儿细菌性肺炎临床效果明显,值得临床推广。

2×3 kW bidirectional output fiber oscillator employing spindle-shaped ytterbium-doped fiber

A 2×3 kW-level bidirectional output fiber oscillator is realized by combining the specially designed spindle-shaped ytterbium-doped fiber,non-wavelength-stabilized 976-nm LDs,and grating bandwidth optimization to balance transverse mode instability and stimulated Raman scattering.The maximum output powers at both ends are 3265 and 2840 W,respectively,with a total efficiency of 73.2%.The M^(2) factors of the lasers at both ends are about 1.98 and 2.38,respectively.The beam profile at both ends shows that a bidirectional output annular beam fiber oscillator has been realized,which has great potential in practical applications.

AIE gel exhibiting continuous gradient fluorescence based on a polar-responsive AIE-gen

Traditional multicolor fluorescent hydrogels are generated through the assembly of discrete fluorescent hydrogels,which is not a complete integration much distinct from living organisms.On the basis of aggregation-induced emission(AIE),a special solvent polar-responsive AIE molecule possessing a twisted intramolecular charge transfer(TICT)effect was noticed.By incorporating it into the gel network,an AIE gel that displays continuous gradient fluorescence was fabricated.First,hydrogel A containing the solvent polar-responsive AIE-gen was prepared to show orange fluorescence.After soaking in the organic solvents,the fluorescence color transition of hydrogel A ranging from orange to green occurred when being immersed in high-polarity organic solvents ascribed to the embedded AIE-gen owning TICT effect.Then,hydrogel A was successively lifted up from organic solvents.Due to the different immersion time of each section for the hydrogel,the polarity difference occurred.Then,the produced gel B showed continuous gradient fluorescence ranging from orange to green under the irradiation of UV light.

Kilowatt-level supercontinuum generation in a single-stage random fiber laser with a half-open cavity

The random distributed-feedback fiber laser(RFL) is a new approach to obtain a high-power stable supercontinuum(SC) source.To consider both structure simplification and high-power SC output,an innovative structure achieving a kilowatt-level SC output in a single-stage RFL with a half-open cavity is demonstrated in this paper.It consists of a fiber oscillator,a piece of long passive fiber and a broadband coupler,among which the broadband coupler acting as a feedback device is crucial in SC generation.When the system has no feedback,the backward output power is up to298 W under the pump power of 1185 W.When the feedback is introduced before the pump laser,the backward power loss can be reduced and the pump can be fully utilized,which could promote forward output power and conversion efficiency significantly.Under the maximum pump power of 1847 W,a 1300 W SC with spectrum ranging from 887 to1920 nm and SC conversion efficiency of 66% is obtained.To the best of our knowledge,it is the simplest structure used for high-power SC generation,and both the generated SC output power and the conversion efficiency are highest in the scheme of the half-opened RFL output SC.

Aggregates of fluorescent gels assembled by interfacial dynamic bonds

Life,defined as the specific form of substance,is an integration of aggregates at various scales,ranging from single molecules to tissues.However,these building blocks of common aggregates are usually recognized as confining at the microscopic level,while there are few studies focusing on macroscopic building blocks for aggregates.Fluorescent gels,as the important macroscopic building blocks,are drawing researchers’attention on account of their extraordinary fluorescence as well as soft material properties.Inspired by nature,fluorescent gels can be aggregated through interfacial adhesion.According to the driving forces for interfacial adhesion,a series of aggregates of fluorescent gels(AFGs)was summarized,including H-bond,metal coordinations,host-guest interactions,hydrophobic interactions,electrostatic interactions,dynamic covalent bonds as well as multiple driving forces.These AFGs own dynamic assembled behaviors and rich stimuli responsiveness,which could be applied to information storage,sensing,biomedical systems,and so on.The authors anticipate this review can accelerate the development of aggregate science,especially based on macroscopic building blocks.

Near-diffraction-limited linearly polarized narrow-linewidth random fiber laser with record kilowatt output

In this paper, we propose and experimentally investigate a linearly polarized narrow-linewidth random fiber laser(RFL) operating at 1080 nm and boost the output power to kilowatt level with near-diffraction-limited beam quality using a master oscillation power amplifier. The RFL based on a half-opened cavity, which is composed of a linearly polarized narrow-linewidth fiber Bragg grating and a 500 m piece of polarization-maintained Ge-doped fiber, generates a 0.71 W seed laser with an 88 pm full width at half-maximum(FWHM) linewidth and a 22.5 dB polarization extinction ratio(PER) for power scaling. A two-stage fiber amplifier enhances the seed laser to the maximal 1.01 k W with a PER value of 17 dB and a beam quality of M_x^2=1.15 and M_y^2=1.13. No stimulated Brillouin scattering effect is observed at the ultimate power level, and the FWHM linewidth of the amplified random laser broadens linearly as a function of the output power with a coefficient of about 0.1237 pm∕W.To the best of our knowledge, this is the first demonstration of a linearly polarized narrow-linewidth RFL with even kilowatt-level near-diffraction-limited output, and further performance scaling is ongoing.

All-fiberized and narrow-linewidth 5 kW power-level fiber amplifier based on a bidirectional pumping configuration

In this paper,an all-fiberized and narrow-linewidth 5 kW power-level fiber amplifier is presented.The laser is achieved based on the master oscillator power amplification configuration,in which the phase-modulated single-frequency laser is applied as the seed laser and a bidirectional pumping configuration is applied in the power amplifier.The stimulated Brillouin scattering,stimulated Raman scattering,and transverse mode instability effects are all effectively suppressed in the experiment.Consequently,the output power is scaled up to 4.92 kW with a slope efficiency of as high as approximately 80%.The 3-dB spectral width is about 0.59 nm,and the beam quality is measured to be M^(2)~1.22 at maximum output power.Furthermore,we have also conducted a detailed spectral analysis on the spectral width of the signal laser,which reveals that the spectral wing broadening phenomenon could lead to the obvious decrease of the spectral purity at certain output power.Overall,this work could provide a reference for obtaining and optimizing high-power narrow-linewidth fiber lasers.

Novel constant-cladding tapered-core ytterbium-doped fiber for high-power fiber laser oscillator

Power scaling based on traditional ytterbium-doped fibers(YDFs)is limited by optical nonlinear effects and transverse mode instability(TMI)in high-power fiber lasers.Here,we propose a novel long tapered fiber with a constant cladding and tapered core(CCTC)along its axis direction.The tapered-core region of the fiber is designed to enhance the stimulated Raman scattering(SRS)threshold and suppress higher-order mode resonance in the laser cavity.The CCTC YDF was fabricated successfully with a modified chemical vapor deposition(MCVD)method combined with solution doping technology,which has a cladding diameter of 400µm and a varying core with a diameter of~24μm at both ends and~31μm in the middle.To test the performance of the CCTC fiber during high-power operation,an all-fiber laser oscillator based on a CCTC YDF was investigated experimentally.As a result,a maximum output power of 3.42 kW was achieved with an optical-to-optical efficiency of 55.2%,although the TMI effect was observed at an output power of~3.12 kW.The measured beam quality(M^(2)factor)was~1.7,and no sign of the Raman component was observed in the spectrum.We believe that CCTC YDF has great potential to simultaneously mitigate the SRS and TMI effects,and further power scaling is promising by optimizing the structure of the YDF.

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.

Powerful Narrow Linewidth Random Fiber Laser

In this paper, we demonstrate a narrow linewidth random fiber laser, which employs a tunable pump laser to select the operating wavelength for efficiency optimization, a narrow-band fiber Bragg grating （FBG） and a section of single mode fiber to construct a half-open cavity, and a circulator to separate pump light input and random lasing output. Spectral linewidth down to 42.31 GHz is achieved through filtering by the FBG. When 8.97 W pump light centered at the optimized wavelength 1036.5nm is launched into the half-open cavity, 1081.4 nm random lasing with the maximum output power of 2.15 W is achieved, which is more powerful than the previous reported results.

Revealing the dynamics of intensity fluctuation transfer in a random Raman fiber laser

Temporal intensity fluctuation is one of the inherent features of fiber lasers.When utilizing the fiber lasers to pump a random Raman fiber laser(RRFL),the intensity fluctuation transfer from the pump to the random lasing could affect the output performance significantly.In this paper,we comprehensively compared the spectral,temporal,and power characteristics of an RRFL pumped by two different fiber lasers—a temporally unstable fiber oscillator and a temporally stable amplified spontaneous emission(ASE)source.Owing to less impact of the intensity fluctuation transfer,the ASE source-pumped RRFL shows∼45.3%higher maximum output power,higher spectral purity(>99.9%)and optical signal-to-noise ratio(>40dB),weaker spectral broadening,and more stable temporal behavior compared to the fiber oscillator-pumped RRFL.Furthermore,based on the temporal-spatial-coupled Raman equations and the generalized nonlinear Schrödinger equations,we numerically revealed the impact of the pump intensity fluctuations on the output characteristics of RRFLs,and found that the temporal walk-off effect played an important role in the dynamics of intensity fluctuation transfer.This work may provide a reference for designing and implementing high-performance RRFLs and promote their practicability in sensing,telecommunications,and high-power applications.

kW-class high power fiber laser enabled by active long tapered fiber

Compared with traditional uniform fibers, tapered fiber has numerous unique advantages, such as larger mode area,higher pump absorption, suppression to nonlinear effects, and maintaining good beam quality. In this manuscript, we have constructed an all-fiberized fiber amplifier which is based on a piece of ytterbium-doped tapered double-clad fiber(T-DCF). The fiber amplifier is operated under continuous wave(CW) regime at 1080 nm wavelength. The M2 factor of the amplifier at 1.39 k W output power is ～1.8. The maximum output power of the system reached 1.47 k W, which, to the best of our knowledge, is the highest output power of long tapered fiber based fiber laser system. Our result successfully verifies the potential of power scalability and all-fiberized capability of long tapered fiber, and the performance of our system can be further enhanced by fiber design optimization.

Denoising for satellite laser altimetry full-waveform data based on EMD-Hurst analysis

Full-waveform decomposition is crucial for obtaining accurate satelliteground distance,the accuracy of which is severely affected by noises.However,the traditional filters all depend on filtering parameters.This paper presents a new and adaptive method for denoising based on empirical mode decomposition(EMD)and Hurst analysis(EMD-Hurst).The noisy full-waveforms are first decomposed into their intrinsic mode functions(IMFs),and the Hurst exponent of each IMF is established by the detrended fluctuation analysis.The IMF is regarded as the highfrequency noise and is deleted if its Hurst exponent is≤0.5.Both simulated and real full-waveforms were conducted to validate and evaluate the method by comparing with six other IMF selection methods via metrics like waveform decomposition consistency ratio(CR),average error of decomposition parameters,and ICESat/GLAS waveformparameter product GLAH05.The comparisons show that:(1)under different SNR conditions,EMD-Hurst performs robustly and obtains a higher CR than other EMD based methods;(2)obtains the highest average CR and a relatively lower average error for the echo parameters;and(3)peak numbers and fitting accuracy for GLAH01 are more reasonable and precise than those of GLAH05,which could offer a good reference for the processing on future space-borne full-waveform data.

Passively spatiotemporal gain-modulation-induced stable pulsing operation of a random fiber laser

Unlike a traditional fiber laser with a defined resonant cavity, a random fiber laser(RFL), whose operation is based on distributed feedback and gain via Rayleigh scattering(RS) and stimulated Raman scattering in a long passive fiber, has fundamental scientific challenges in pulsing operation for its remarkable cavity-free feature. For the time being, stable pulsed RFL utilizing a passive method has not been reported. Here, we propose and experimentally realize the passive spatiotemporal gain-modulation-induced stable pulsing operation of counterpumped RFL. Thanks to the good temporal stability of an employed pumping amplified spontaneous emission source and the superiority of this pulse generation scheme, a stable and regular pulse train can be obtained.Furthermore, the pump hysteresis and bistability phenomena with the generation of high-order Stokes light is presented, and the dynamics of pulsing operation is discussed after the theoretical investigation of the counterpumped RFL. This work extends our comprehension of temporal property of RFL and paves an effective novel avenue for the exploration of pulsed RFL with structural simplicity, low cost, and stable output.

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.

A 3.5-kW near-single-mode oscillating-amplifying integrated fiber laser

The fiber laser based on an oscillating-amplifying integrated structure has the potential to benefit from the advantages of a fiber laser oscillator and amplifier with the characteristics of strong anti-back-reflected light ability and high efficiency.Here,we achieved a 3.5-kW near-single-mode(M^(2)~1.24)oscillating-amplifying integrated fiber laser with an active fiber length of 8 m in the oscillating section and 17.6 m in the amplifying section.While operating at the maximum power,the optical-to-optical conversion efficiency is 87.0%,and the intensity of stimulated Raman scattering is about23.61 dB lower than that of the signal light.To the best of the authors’knowledge,this is the highest output power of an oscillating-amplifying integrated fiber laser,accompanied with the best beam quality and the highest efficiency.

Energy recovery in China from solid wastes by the moving grate and circulating fluidized bed technologies

In recent years,the Chinese waste-to-energy(WTE)industry is growing at the rate of about thirty new plants each year.The municipal solid waste(MSW)fuel has a low heating value of 4-7 MJ/kg,in comparison to about 11 MJ/kg in U.S.and 8-11 MJ/kg in EU.Combustion of the low heating value fuel on a moving grate(MG),the dominant combustion technology worldwide,is difficult to control and measures have to be taken to remove some moisture prior to combustion.For this and other reasons,an alternative technology,the circulating fluid bed(CFB)has been implemented in China.This paper is a comparative study of the two technologies and was carried out by Columbia University and two senior engineers,representing the MG and CFB technologies of China.Data were derived from industrial operating plants and from the literature.The fuel to MG furnaces is as-received MSW,while the MSW to CFB reactors is pre-shredded using high-torque low-speed shredders.The availability of MG plants,over a 1-year period,is 90%+,while that of CFB facilities is 80%+.Also,the in-plant electricity consumption of MG plants is slightly lower than the consumption of CFB plants.The MG furnace is less compact,than that of a CFB combustion chamber,with a heat flux range from 0.5 to 0.6 MW/m^(2) of grate surface area,while that of CFB furnace was about 1.7 MW/m^(2) of furnace cross-section.The bottom ash in a MG process is typically wet-discharged and the recovery of metals is less efficient.A drawback of the CFB process is that the fly ash generated is 5-10%of the weight of MSW combusted,as compared to 1-3%for moving grate plants in China.