Strong-field Ionization Of Gold Nanoparticles

As a bridge between the macroscopic matter and microscopic atomic-molecular,the strong-field ionization of nanoparticles plays a crucial role in understanding fundamental physics and chemical reaction processes.When nanoparticles are exposed in the strong-field,the near-field enhancement effect occurs due to the dielectric confinement effect.The near-field enhancement can greatly affect the result of the interaction between nanoparticles and laser.When it comes to the strong-field ionization of nanoparticles,the effect of surface molecules from nanoparticles can not be ignored.When the surface molecules are ionized,related processes,such as electron emission and collision,will be triggered,which will affect the emission behavior of electrons and ions inside the nanoparticles.At the same time,the properties of nanoparticles,such as their size and shape,also have a huge impact on the near-field enhancement,so that it is of great significance to explore the strong-field ionization nanoparticles.Using single-shot nano-VMI(velocity map imaging)technology,the complex physical process can be researched from a new perspective.It is also an important guide for controlled nanoscale ion-source devices and femtosecond laser processing.In this paper,we focus on the ionization of gold nanoparticles interacting with ultrafast laser pulses.Based on the single-shot nano-VMI system,the electrons and ions momentum distributions can be imaged.The finite element analysis(FEA)methods are applied to simulate and analyze the Mie scattering.The main research achievements and innovations are as follows:1.Improving the finite element analysis method for near-field enhancement simulation of nanoparticles with different shapes.The traditional FEA method is based on the open source software ANSYS,and the Mie scattering is simulated by the Finite Difference Time Domain(FDTD).For highly symmetric structures,the near-field enhancement distribution obtained by this method is relatively accurate.However,for some nanoparticles with spatial structure,the FDTD method becomes inapplicable,and the spatial grid division needs to be more refined.The discontinuous Galerkin time domain(DGTD)method is used to study gold nanocubes.This method is able to simulate the near-field enhancement distribution of nanoparticles with spatial structure,which fits well with the experimental results.It provides a new method and solution for the simulation of complex structures.2.Based on the single-shot momentum distribution of surface molecular from nanoparticles,the ionization of metal nanoparticles is been researched.The ionization of gold nanoparticles is investigated through single-shot nano-VMI system.Using beam source system,VMI and high speed camera,the angle-resolved momentum distributions can be acquired for understading the strong-field ionization of nano-system.The main object of this study is gold nanoparticles.It is found that gold nanoparticles are able to generate stronger near-field enhancement distribution and have metal shielding effect in the ionization process.This study provides a new way to explore the interaction between unique nanosystem and ultrafast laser.3.Study the surface molecular ionization of gold nanocubes,and investigate the influence brought by shape change on the interaction process.The shape of gold nanoparticles is changed to explore the ionization image of gold nanocubes.Polarization-dependent ions emission and shock-wave generation are observed.The influence of structural change on the interaction process between nanoparticles and laser was analyzed.The mode inversion of the initial near-field distribution by momentum images reveals the modulating effect of near-field enhancement on the ionization process.This experiment provides a new strategy for potential applications such as controlled ion design.