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Dive into the research topics where Helong Li is active.

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Featured researches published by Helong Li.


New Journal of Physics | 2013

Remote creation of coherent emissions in air with two-color ultrafast laser pulses

Jinping Yao; Guihua Li; Chenrui Jing; Bin Zeng; Wei Chu; Jielei Ni; Haisu Zhang; Hongqiang Xie; Chaojin Zhang; Helong Li; Huailiang Xu; S. L. Chin; Ya Cheng; Zhizhan Xu

We experimentally demonstrate the generation of narrow-bandwidth emissions with excellent coherent properties at 391 and 428nm from N + (B 2 6 + (v 0 = 0) ! X 2 6 + g (v = 0,1)) inside a femtosecond filament in air by an orthogonally polarized two-color driver field (i.e. 800nm laser pulse and its second harmonic). The durations of the coherent emissions at 391 and 428nm are measured to be 2.4 and 7.8ps, respectively, both of which are much longer than the duration of the pump and its second harmonic pulses. Furthermore,


Optics Letters | 2013

Sensing combustion intermediates by femtosecond filament excitation

Helong Li; Huailiang Xu; Bo-Si Yang; Qi-Dai Chen; Tao Zhang; Hong-Bo Sun

Simultaneous monitoring of multiple combustion intermediates using femtosecond filament-induced nonlinear spectroscopy is demonstrated. Clean fluorescence emissions from free radicals CH, CN, NH, OH, and C(2), as well as atomic C and H, are observed when a femtosecond filament is formed in the laminar ethanol/air flame on an alcohol burner. The fluorescence signals of these species are found to vary as functions of the position of interaction of the filament with the flame along the vertical axis of the central combusting flow, opening up a possibility for remote combustion diagnostic in engines by the excitation of femtosecond laser filament.


Applied Physics Letters | 2014

Lasing action induced by femtosecond laser filamentation in ethanol flame for combustion diagnosis

Wei Chu; Helong Li; Jielei Ni; Bin Zeng; Jinping Yao; Haisu Zhang; Guihua Li; Chenrui Jing; Hongqiang Xie; Huailiang Xu; Kaoru Yamanouchi; Ya Cheng

We experimentally demonstrate the generation of lasing action in the laminar ethanol/air flame on an alcohol burner array using femtosecond laser filament excitation. By probing the backward emissions of combustion species, it is found that as the interaction length of the filament in the flame increases, the signals intensity at the 388 nm band for the B2Σ−X2Σ transition of CN increases exponentially, but that at the 474 nm band for A3Πg−X′3Πu transition of C2 increases linearly. The exponential behavior of the CN emissions is ascribed to amplified spontaneous emission, which opens up a way to overcome the quenching effect of specific species in combustion diagnosis.


Scientific Reports | 2016

Simultaneous identification of multi-combustion-intermediates of alkanol-air flames by femtosecond filament excitation for combustion sensing.

Helong Li; Wei Chu; Huailiang Xu; Ya Cheng; S. L. Chin; Kaoru Yamanouchi; Hong-Bo Sun

Laser filamentation produced by the propagation of intense laser pulses in flames is opening up new possibility in application to combustion diagnostics that can provide useful information on understanding combustion processes, enhancing combustion efficiency and reducing pollutant products. Here we present simultaneous identification of multiple combustion intermediates by femtosecond filament excitation for five alkanol-air flames fueled by methanol, ethanol, n-propanol, n-butanol, and n-pentanol. We experimentally demonstrate that the intensities of filament-induced photoemission signals from the combustion intermediates C, C2, CH, CN increase with the increasing number of carbons in the fuel molecules, and the signal ratios between the intermediates (CH/C, CH/C2, CN/C, CH/C2, CN/CH) are different for different alkanol combustion flames. Our observation provides a way for sensing multiple combustion components by femtosecond filament excitation in various combustion conditions that strongly depend on the fuel species.


Optics Express | 2016

Critical power and clamping intensity inside a filament in a flame.

Helong Li; Wei Chu; Hongwei Zang; Huailiang Xu; Ya Cheng; S. L. Chin

We report on measurements of both the critical power for self-focusing of a Ti: Sapphire 800 nm femtosecond laser and the peak intensity clamped inside a single filament in an ethanol-air flame on an alcohol burner array. By observing the shift of focal position of femtosecond laser pulses, we determine the critical power in the flame to be 2.2 ± 0.3 GW, which is 4-5 times smaller than the usually quoted one in air. The clamped laser intensity inside the filament is measured to be roughly half of that in air. Our results provide insights into the understanding of femtosecond laser filamentation in flames for practical application of combustion diagnostics.


Langmuir | 2018

Intense Femtosecond Laser-Mediated Electrical Discharge Enables Preparation of Amorphous Nickel Phosphide Nanoparticles

Zhuo-Chen Ma; Qi-Dai Chen; Bing Han; Helong Li; Lei Wang; Yong-Lai Zhang; Hong-Bo Sun

Reported here is a high-efficiency preparation method of amorphous nickel phosphide (Ni-P) nanoparticles by intense femtosecond laser irradiation of nickel sulfate and sodium hypophosphite aqueous solution. The underlying mechanism of the laser-assisted preparation was discussed in terms of the breaking of chemical bond in reactants via highly intense electric field discharge generated by the intense femtosecond laser. The morphology and size of the nanoparticles can be tuned by varying the reaction parameters such as ion concentration, ion molar ratio, laser power, and irradiation time. X-ray diffraction and transmission electron microscopy results demonstrated that the nanoparticles were amorphous. Finally, the thermogravimetric-differential thermal analysis experiment verified that the as-synthesized noncrystalline Ni-P nanoparticles had an excellent catalytic capability toward thermal decomposition of ammonium perchlorate. This strategy of laser-mediated electrical discharge under such an extremely intense field may create new opportunities for the decomposition of molecules or chemical bonds that could further facilitate the recombination of new atoms or chemical groups, thus bringing about new possibilities for chemical reaction initiation and nanomaterial synthesis that may not be realized under normal conditions.


Chinese Physics Letters | 2016

Differentiation of Positional Isomers of Propyl Alcohols Using Filament-Induced Fluorescence*

Xiang-Ye Wei; Zhi-Wei Tu; Chang Liu; Helong Li; Huailiang Xu

We experimentally demonstrate the recognition of positional isomers of propyl alcohol vapor through nonlinear fluorescence induced by high-intensity femtosecond laser filaments in air. By measuring characteristic fluorescence of n-propyl and isopropyl alcohol vapors produced by femtosecond filament excitation, it is found that they show identical spectra, that is, those from molecular bands of CH, C2, NH, OH and CN, while the relative intensities are different. By comparing the ratios of the CH and C2 signals, the two propyl alcohol isomers are differentiated. The different signal intensities are ascribed to different ionization potentials of the two isomer molecules, leading to different production efficiencies of fluorescing fragments.


Sensors and Actuators B-chemical | 2014

Femtosecond laser filamentation for sensing combustion intermediates: A comparative study

Helong Li; Xiang-Ye Wei; Huailiang Xu; S. L. Chin; Kaoru Yamanouchi; Hong-Bo Sun


Journal of Lightwave Technology | 2018

Stretchable PEG-DA Hydrogel-Based Whispering-Gallery-Mode Microlaser with Humidity Responsiveness

Qiu-Lan Huang; Huailiang Xu; Mu‐Tian Li; Zhi-Shan Hou; Chao Lv; Xue-Peng Zhan; Helong Li; Hong Xia; Hai-Yu Wang; Hong-Bo Sun


Journal of Optics | 2017

Generation of air lasing at extended distances by coaxial dual-color femtosecond laser pulses

Helong Li; Hongwei Zang; Yue Su; Yao Fu; Huailiang Xu

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Ya Cheng

Chinese Academy of Sciences

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Bin Zeng

Chinese Academy of Sciences

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Guihua Li

Chinese Academy of Sciences

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Haisu Zhang

Chinese Academy of Sciences

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