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Low bending loss waveguide opens the avenue to downsizing of 3D photonic integrated circuits

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Science China(Physics,Mechanics & Astronomy) 2018年第7期61卷 103-104页

作者： yongfeng lu Department of Electrical and Computer Engineering University of Nebraska

Photonic integrated circuits(PIC)enable efficient and flexible control of photons within a compact space,thereby revolutionizing both information technology and biological and chemical sensing.Currently,semiconductor materials including silicon,silicon nitride(Si N),and indium phosphate(In P)are still the prominent PIC platforms,which can be patterned using mature photolithographic technologies[1].

关键词：集成电路波导损失弯曲 3D 信息技术半导体材料制造技术

Foreword for the inaugural issue

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International Journal of Extreme Manufacturing 2019年第1期1卷 1-2页

作者： Dongming Guo yongfeng lu Key Laboratory for Precision and Non-traditional Machining Technology of Ministry of Education Dalian University of TechnologyDalianPeople’s Republic of China University of Nebraska-Lincoln LincolnNE 68588United States of America

The International Journal of Extreme Manufacturing is a leading,worldwide scientific journal focused on the fields of extreme manufacturing.Published within it are the latest scientific and engineering achievements in... 详细信息

关键词： journal extreme technological

Ultrafast optical response and ablation mechanisms of molybdenum disulfide under intense femtosecond laser irradiation

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Light(Science & Applications) 2020年第1期9卷 1265-1272页

作者： Changji Pan Lan Jiang Jingya Sun Qingsong Wang Feifei Wang Kai Wang yongfeng lu Yeliang Wang Liangti Qu Tianhong Cui Laser Micro/Nano-Fabrication Laboratory School of Mechanical EngineeringBeijing Institute of Technology100081 BeijingP.R.China Department of Electrical Engineering University of Nebraska-LincolnLincolnNE 68588-0511USA School of Information and Electronics Beijing Institute of Technology100081 BeijingP.R.China Key Laboratory for Advanced Materials Processing Technology Ministry of Education of ChinaDepartment of Mechanical EngineeringTsinghua University100084 BeijingP.R.China Department of Mechanical Engineering University of MinnesotaMinneapolisMN 55455USA

Numerous valuable studies on electron dynamics have focussed on the extraordinary properties of molybdenum disulfide(MoS_(2));however,most of them were confined to the level below the damage threshold.Here the electron dynamics of MoS_(2) under intense ultrafast laser irradiation was investigated by experiments and simulations.Two kinds of ablation mechanisms were revealed,which led to two distinct types of electron dynamics and final ablation morphology.At a higher fluence,the emergence of superheated liquid induced a dramatic change in the transient reflectivity and micro-honeycomb structures.At a lower fluence,the material was just removed by sublimation,and the ablation structure was relatively flat.X-ray photoelectron spectroscopic(XPS)measurements demonstrated that thermal decomposition only occurred at the higher fluence.Furthermore,a theoretical model was developed to deeply reveal the ultrafast dynamics of MoS_(2) ablation.The simulation results were in good agreement with the temporal and spatial reflectivity distribution obtained from the experiment.The electron and lattice temperature evolution was also obtained to prove the ablation mechanism.Our results revealed ultrafast dynamics of MoS_(2) above the damage threshold and are helpful for understanding the interaction mechanism between MoS_(2) and intense ultrafast lasers,as well as for MoS_(2) processing applications.

关键词： intense molybdenum disulfide

Enhancing the expansion of a plasma shockwave by crater-induced laser refocusing in femtosecond laser ablation of fused silica

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Photonics Research 2017年第5期5卷 488-493页

作者： QINGSONG WANG LAN JIANG JINGYA SUN CHANGJI PAN WEINA HAN GUOYAN WANG HAO ZHANG COSTAS P.GRIGOROPOULOS yongfeng lu Laser Micro/Nano Fabrication Laboratory School of Mechanical Engineering Beijing Institute of Technology Laser Thermal Laboratory Department of Mechanical Engineering University of California Department of Electrical and Computer Engineering University of Nebraska-Lincoln

The dynamics of plasma and shockwave expansion during two femtosecond laser pulse ablation of fused silica are studied using a time-resolved shadowgraph imaging technique. The experimental results reveal that during the second pulse irradiation on the crater induced by the first pulse, the expansion of the plasma and shockwave is enhanced in the longitudinal direction. The plasma model and Fresnel diffraction theory are combined to calculate the laser intensity distribution by considering the change in surface morphology and transient material properties. The theoretical results show that after the free electron density induced by the rising edge of the pulse reaches the critical density, the originally transparent surface is transformed into a transient high-reflectivity surface(metallic state). Thus, the crater with a concave-lens-like morphology can tremendously reflect and refocus the latter part of the laser pulse, leading to a strong laser field with an intensity even higher than the incident intensity. This strong refocused laser pulse results in a stronger laser-induced air breakdown and enhances the subsequent expansion of the plasma and shockwave. In addition, similar shadowgraphs are also recorded in the single-pulse ablation of a concave microlens, providing experimental evidence for the enhancement mechanism.

关键词： exp Enhancing the expansion of a plasma shockwave by crater-induced laser refocusing in femtosecond laser ablation of fused silica

Ultrafast dynamics observation during femtosecond laser-material interaction

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International Journal of Extreme Manufacturing 2019年第3期1卷 62-84页

作者： Baoshan Guo Jingya Sun yongfeng lu Lan Jiang Laser Micro/Nano Fabrication Laboratory School of Mechanical EngineeringBeijing Institute of TechnologyBeijing100081People’s Republic of China Department of Electrical and Computer Engineering University of Nebraska-LincolnLincolnNE 68588-0511United States of America

Femtosecond laser technology has attracted significant attention from the viewpoints of fundamental and application;especially femtosecond laser processing materials present the unique mechanism of laser-material interaction.Under the extreme nonequilibrium conditions imposed by femtosecond laser irradiation,many fundamental questions concerning the physical origin of the material removal process remain unanswered.In this review,cutting-edge ultrafast dynamic observation techniques for investigating the fundamental questions,including timeresolved pump-probe shadowgraphy,ultrafast continuous optical imaging,and four-dimensional ultrafast scanning electron microscopy,are comprehensively surveyed.Each technique is described in depth,beginning with its basic principle,followed by a description of its representative applications in laser-material interaction and its strengths and limitations.The consideration of temporal and spatial resolutions and panoramic measurement at different scales are two major challenges.Hence,the prospects for technical advancement in this field are discussed finally.

关键词： ultrafast dynamics pump-probe shadowgraphy ultrafast continuous optical imaging 4D ultrafast scanning electron microscopy femtosecond laser manufacturing

Laser-based micro/nanofabrication in one, two and three dimensions

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Frontiers of Optoelectronics 2015年第4期8卷 351-378页

作者： Wei XIONG Yunshen ZHOU Wenjia HOU Lijia JIANG Masoud MAHJOURI-SAMANI Jongbok PARK Xiangnan HE Yang GAO Lisha FAN Tommaso BALDACCHINI Jean-Francois SILVAIN yongfeng lu Department of Electrical Engineering University of Nebraska-Lincoln Lincoln NE 68588 USA Technology and Applications Center Newport Corporation Irvine CA 92606 USA Institute of Chemistry of Condensed Matter of Bordeaux ICMCB-CNRS 87 Avenue du Docteur Albert Schweitzer F-33608 Pessac Cedex France

Advanced micro/nanofabrication of functional materials and structures with various dimensions represents a key research topic in modem nanoscience and technology and becomes critically important for numerous emerging technologies such as nanoelectronics, nanopho- tonics and micro/nanoelectromechanical systems. This review systematically explores the non-conventional material processing approaches in fabricating nanomaterials and micro/nanostructures of various dimensions which are challenging to be fabricated via conventional approaches. Research efforts are focused on laser-based techniques for the growth and fabrication of one-dimensional （1D）, two-dimensional （2D） and three-dimensional （3D） nanomaterials and micro/nanostructures. The following research topics are covered, including： 1） laser-assisted chemical vapor deposition （CVD） for highly efficient growth and integration of 1D nanomaterial of carbon nanotubes （CNTs）, 2） laser direct writing （LDW） of graphene ribbons under ambient conditions, and 3） LDW of 3D micro/nanostructures via additive and subtractive processes. Comparing with the conventional fabrication methods, the laser-based methods exhibit several unique advantages in the micro/nanofabrication of advanced functional materials and structures. For the 1D CNT growth, the laser-assisted CVD process can realize both rapid material synthesis and tight control of growth location and orientation of CNTs due to the highly intense energy delivery and laser-induced optical near-field effects. For the 2D graphene synthesis and patterning, roomtemperature and open-air fabrication of large-scale graphene patterns on dielectric surface has been successfully realized by a LDW process. For the 3D micro/nanofabrica- tion, the combination of additive two-photon polymeriza- tion （TPP） and subtractive multi-photon ablation （MPA） processes enables the fabrication of arbitrary complex 3D micro/nanostructures which tional fabrication methods are challenging for conven- Considering the numerous unique advantages of las

关键词： micro/nanofabrication laser material interac-tion carbon nanotubes （CNTs） graphene two-photonpolymerization （TPP） multi-photon ablation （MPA）

Structure-Mediated Excitation of Air Plasma and Silicon Plasma Expansion in Femtosecond Laser Pulses Ablation

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Research 2018年第1期2018卷 152-162页

作者： Qingsong Wang Lan Jiang Jingya Sun Changji Pan Weina Han Guoyan Wang Feifei Wang Kaihu Zhang Ming Li yongfeng lu Laser Micro/Nano Fabrication Laboratory School of Mechanical EngineeringBeijing Institute of TechnologyBeijing 100081China Beijing Engineering Research Center of Applied Laser Technology Institute of Laser EngineeringBeijing University of TechnologyBeijing 100124China Beijing Spacecrafs China Academy of Space TechnologyBeijing 100094China State Key Laboratory of Transient Optics and Photonics Xi’an Institute of Optics and Precision MechanicsChinese Academy of SciencesXi’an 710119China Department of Electrical and Computer Engineering University of Nebraska-LincolnLincolnNE 68588-0511USA

Femtosecond laser-induced surface structures upon multiple pulses irradiation are strongly correlated with the pulse number,which in turn signifcantly afects successive laser-material interactions.By recording the dynamics of femtosecond laser ablation of silicon using time-resolved shadowgraphy,here we present direct visualization of the excitation of air plasma induced by the refected laser during the second pulse irradiation.Te interaction of the air plasma and silicon plasma is found to enhance the shockwave expansion induced by silicon ablation in the longitudinal direction,showing anisotropic expansion dynamics in diferent directions.We further demonstrate the vanishing of air plasma as the pulse number increases because of the generation of a rough surface without light focusing ability.In the scenario,the interaction of air plasma and silicon plasma disappears;the expansion of the silicon plasma and shockwave restores its original characteristic that is dominated by the laser-material coupling.Te results show that the excitation of air plasma and the laser-material coupling involved in laser-induced plasma and shockwave expansion are structure mediated and dependent on the pulse number,which is of fundamental importance for deep insight into the nature of laser-material interactions during multiple pulses ablation.

关键词： Femto expansion second

Hybrid superhydrophilic-superhydrophobic micro/nanostructures fabricated by femtosecond laserinduced forward transfer for sub-femtomolar Raman detection

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Microsystems & Nanoengineering 2019年第1期5卷 207-216页

作者： Xiaodan Ma Lan Jiang Xiaowei Li Bohong Li Ji Huang Jiaxing Sun Zhi Wang Zhijie Xu Liangti Qu yongfeng lu Tianhong Cui Laser Micro/Nano Fabrication Laboratory School of Mechanical EngineeringBeijing Institute of Technology100081 BeijingChina Department of Mechanical Engineering Tsinghua University100084 BeijingChina School of Chemistry and Chemical Engineering Beijing Institute of Technology100081 BeijingChina Department of Electrical and Computer Engineering University of Nebraska-LincolnLincolnNE 68588-0511USA Department of Mechanical Engineering University of MinnesotaMinneapolisMN 55455USA

Raman spectroscopy plays a crucial role in biochemical analysis.Recently,superhydrophobic surface-enhanced Raman scattering(SERS)substrates have enhanced detection limits by concentrating target molecules into small areas.However,due to the wet transition phenomenon,further reduction of the droplet contact area is prevented,and the detection limit is restricted.This paper proposes a simple method involving femtosecond laser-induced forward transfer for preparing a hybrid superhydrophilic–superhydrophobic SERS(HS-SERS)substrate by introducing a superhydrophilic pattern to promote the target molecules to concentrate on it for ultratrace detection.Furthermore,the HS-SERS substrate is heated to promote a smaller concentrated area.The water vapor film formed by the contact of the solution with the substrate overcomes droplet collapse,and the target molecules are completely concentrated into the superhydrophilic region without loss during evaporation.Finally,the concentrated region is successfully reduced,and the detection limit is enhanced.The HS-SERS substrate achieved a final contact area of 0.013mm2,a 12.1-fold decrease from the unheated case.The reduction of the contact area led to a detection limit concentration as low as 10−16 M for a Rhodamine 6G solution.In addition,the HS-SERS substrate accurately controlled the size of the concentrated areas through the superhydrophilic pattern,which can be attributed to the favorable repeatability of the droplet concentration results.In addition,the preparation method is flexible and has the potential for fluid mixing,fluid transport,and biochemical sensors,etc.

关键词： heated limit transfer

Quantifying freeze-melt dynamics of lakes on the Tibetan Plateau using Sentinel-1 synthetic aperture radar imagery

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Journal of Mountain Science 2024年第3期21卷 805-819页

作者： JIN lu CHEN Jun CAI Yu KONG Yecheng WANG yongfeng DUAN Zheng School of Environment and Energy Engineering Anhui Jianzhu UniversityHefei 230601China Anhui Engineering and Technology Research Center for Smart City Anhui Jianzhu UniversityHefei 230601China School of Geographic and Oceanographic Sciences Nanjing UniversityNanjing 210023China Department of Physical Geography and Ecosystem Science Lund UniversityLund 22362Sweden

The ice phenology of alpine lakes on the Tibetan Plateau(TP)is a rapid and direct responder to climate changes,and the variations in lake ice exhibit high temporal frequency characteristics.MODIS and passive microwave data are widely used to monitor lake ice changes with high temporal resolution.However,the low spatial resolutions make it difficult to effectively quantify the freeze-melt dynamics of lakes.This work used Sentinel-1 synthetic aperture radar(SAR)data to derive high-resolution ice maps(about 6 days),then with the aid of Sentinel-2 optical images to quantify freeze-melt processes in three typical lakes on the TP(e.g.Selin Co,Ayakekumu Lake,and Nam Co).The results showed that three lakes had an average annual ice period of 125-157 days and a complete ice cover period of 72-115 days,from 2018 to 2022.They exhibit different ice phenology patterns.Nam Co is characterized by repeated episodes of freezing,melting,and refreezing,resulting in a prolonged freeze-up period.Meanwhile,the break-up period of Nam Co lasts for a longer duration(about 19 days),and the break-up exhibits a smooth process.Similarly,Ayakekumu Lake showed more significant inter-annual fluctuations in the freeze-up period,with deviations of up to 28 days observed among different years.Compared to the other two lakes,Selin Co experienced a relatively short freeze-up and break-up period.In short,Sentinel-1 SAR data can effectively monitor the weekly and seasonal variations in lake ice on the TP.Particularly,this data facilitates quantification of the freeze-melt dynamics.

关键词： Lake ice Sentinel-1 SAR Tibetan Plateau Climate change