There exists an increasing demand of industrial-scale production of high-purity ligand-free nanoparticles due to the continuous development of biomedicine, catalysis, and energy applications. In this contribution, a s...There exists an increasing demand of industrial-scale production of high-purity ligand-free nanoparticles due to the continuous development of biomedicine, catalysis, and energy applications. In this contribution, a simultaneous spatial and temporal focusing(SSTF) setup is first proposed for increasing nanoparticle productivity of the eco-friendly pulsed laser ablation in liquids(PLAL) technique. In spite of the fact that femtosecond pulses have proved to achieve higher ablation rates in air than picosecond pulses, in PLAL this is reversed due to the nonlinear energy losses in the liquid. However, thanks to the incorporation of SSTF, the energy delivered to the target is increased up to 70%, which leads to a nanoparticle production increase of a 2.4 factor. This breaks a barrier toward the employment of femtosecond lasers in high-efficiency PLAL.展开更多
Invisibility or unhearability cloaks have been made possible by using metamaterials enabling light or sound to fow around obstacle without the trace of refections or shadows.Metamaterials are known for being fexible b...Invisibility or unhearability cloaks have been made possible by using metamaterials enabling light or sound to fow around obstacle without the trace of refections or shadows.Metamaterials are known for being fexible building units that can mimic a host of unusual and extreme material responses,which are essential when engineering artifcial material properties to realize a coordinate transforming cloak.Bending and stretching the coordinate grid in space require stringent material parameters;therefore,small inaccuracies and inevitable material losses become sources for unwanted scattering that are decremental to the desired efect.Tese obstacles further limit the possibility of achieving a robust concealment of sizeable objects from either radar or sonar detection.By using an elaborate arrangement of gain and lossy acoustic media respecting parity-time symmetry,we built a one-way unhearability cloak able to hide objects seven times larger than the acoustic wavelength.Generally speaking,our approach has no limits in terms of working frequency,shape,or size,specifcally though we demonstrate how,in principle,an object of the size of a human can be hidden from audible sound.展开更多
基金Generalitat Valenciana(AICO/2016/036,PROMETEU/2016/079)Universitat Jaume I(UJI·B2016-19)Ministerio de Economía y Competitividad(FIS2016-75618-R)
文摘There exists an increasing demand of industrial-scale production of high-purity ligand-free nanoparticles due to the continuous development of biomedicine, catalysis, and energy applications. In this contribution, a simultaneous spatial and temporal focusing(SSTF) setup is first proposed for increasing nanoparticle productivity of the eco-friendly pulsed laser ablation in liquids(PLAL) technique. In spite of the fact that femtosecond pulses have proved to achieve higher ablation rates in air than picosecond pulses, in PLAL this is reversed due to the nonlinear energy losses in the liquid. However, thanks to the incorporation of SSTF, the energy delivered to the target is increased up to 70%, which leads to a nanoparticle production increase of a 2.4 factor. This breaks a barrier toward the employment of femtosecond lasers in high-efficiency PLAL.
基金This work was supported by the National Key R&D Program of China(Grant No.2017YFA0303700)the National Natural Science Foundation of China(Grant No.11634006)+2 种基金the Innovation Special Zone of National Defense Science and Technology.Te authors would like to thank Prof.Jing Lu and Prof.Jian-cheng Tao for fruitful discussions.Daniel Torrent acknowledges the support from the MINECO through a Ramon y Cajal grant(Grant no.RYC-2016-21188)Johan Christensen acknowledges the support from the European Research Council(ERC)through the Starting Grant no.714577 PHONOMETA and from the MINECO through a Ramon y Cajal grant(Grant no.RYC-2015-17156)Johan Christensen would like to thank Romain Fleury and Andrea Alu for helpful suggestions and stimulating discussions.
文摘Invisibility or unhearability cloaks have been made possible by using metamaterials enabling light or sound to fow around obstacle without the trace of refections or shadows.Metamaterials are known for being fexible building units that can mimic a host of unusual and extreme material responses,which are essential when engineering artifcial material properties to realize a coordinate transforming cloak.Bending and stretching the coordinate grid in space require stringent material parameters;therefore,small inaccuracies and inevitable material losses become sources for unwanted scattering that are decremental to the desired efect.Tese obstacles further limit the possibility of achieving a robust concealment of sizeable objects from either radar or sonar detection.By using an elaborate arrangement of gain and lossy acoustic media respecting parity-time symmetry,we built a one-way unhearability cloak able to hide objects seven times larger than the acoustic wavelength.Generally speaking,our approach has no limits in terms of working frequency,shape,or size,specifcally though we demonstrate how,in principle,an object of the size of a human can be hidden from audible sound.
