Preparation Of An Aerodynamic Lens System For The Investigation Of Strong Field Ionization Of Nanoparticles

Aerodynamic lens(ADL)was designed by Peng Liu et al in 1995 and has been widely used in particle mass spectrometer,material synthesis and microscale device fabrication,etc.The aerodynamic lens was designed as a multi-stage orifice plates structure obeyed the aerodynamics principle.When the aerosol goes through these orifices,the particle track line and carrier gas track line are separated in the process of shrinkage and expansion,thus the particles are gathered to the axis.By designing the diameter of the orifice and the length and shape of the spacer,the aerodynamic lens can be applied to the particles with different particle diameter and density.Because of the flexibility of aerodynamic lens structure,aerodynamic lens has developed a lot of styles for different particle size range and different carrier gases.The purpose of the aerodynamic lens is to focus particles which improves the concentration of particles and provides narrow particle beam,thus it provides a reliable and constantly refreshed particle source for the experiments on particles.As a kind of particle beam source,aerodynamic lens is very important for the strong field ionization experiment of solid.The aerodynamic lens forms a micron-scale particle beam,which concentrates most particles.This is suitable for the micron-scale spot diameter of the focused laser,which greatly improves the interaction efficiency between particles and laser.Furthermore,the nanoparticle beam generated by the aerodynamic lens is constantly refreshed in the laser action region,so higher laser light intensity which exceeds the damage threshold of solid particle can be used in experiments.At the same time,the ability of aerodynamic lens to provide micron-scale beam can also be applied to the growth and fabrication of micro devices in nano-optics.Nanoparticles are widely found in the earth's atmosphere,planets and space,where they are involved in diverse chemical and physical processes.Compared with bulk materials,the surface,size and shape of nanoparticles all affect the properties of nanoparticles,showing different characteristics from bulk materials.Therefore,the research on nanoparticles is of vital significance.The detection of photoelectrons(ions)ionized from nanoparticles in strong fields is an effective method to investigate the properties of nanoparticles.Different properties of nanoparticles will lead to different properties of photoelectrons(ions),so the properties of nanoparticles can be explored through the detection of photoelectrons(ions).Meanwhile,as laser pulses was developed into the attosecond domain,the detection of electron movement in solids at attosecond scales becomes a reality.And as nanoparticles without substrates,they will be an excellent research objects.In this paper,firstly the production and treatment of aerosols are introduced from aerosol generation and aerosol drying to aerosol neutralization and particle diameter filtrating through differential mobility analyzer.Then,the design theory of aerodynamic lens is introduced in detail.Two kinds of aerodynamic lens are designed for transporting nanoparticles with a particle size range of 10-1000 nm,and their evaluations are carried out by theoretical calculation.Through comparing the advantages and disadvantages of this two schemes,the influence of aerodynamic lens parameters on the transmission efficiency of nanoparticles is illustrated.Then,the assembly and test of aerodynamic lens and vacuum chamber are completed.Although there is a distance compared with the theory,the diameter of focused nanoparticles beam has been controlled in 1-2 mm.Meanwhile,the improvement of aerodynamic lens was described.The improvement mainly focuses on the structure of inlet orifice and relaxation chamber in order to further improve the transmission efficiency of nanoparticles.The application of aerodynamic lens system in nanoparticles strong field ionization is realized by combining aerodynamic lens with velocity map imaging technique.The momentum distribution of photoelectron and photoion of Si O₂ and Ti O₂ was detected,and it was verified that the aerodynamic lens had a good transmission efficiency for nanoparticles.Meanwhile,it was also suitable for the experiment of the laser intensity exceeding the damage threshold of nanoparticles.Combined with photoion detection experiment and FDTD simultaion,the ability of Ti O₂ photoion yield angular distribution to characterize the surface plasmon field distribution of nanoparticles was verified.