Strong-light-induced Ionization Of Xenon Dimers,Water Clusters And Water Clouds

Considering the interaction between light and matters,strong-light-induced ioniza-tion of matters is a significant phenomenon,which reveals the abundant inner structure of physical world.In this dissertation,the strong-light-induced ionization processes of mat-ters,including the micro atoms and molecules,clusters,macro aqueous medium,droplets and the large-scale water clouds,are investigated.For the strong-light-induced ionization processes of atoms and molecules,the mo-mentum distribution and kinetic energy distribution of photoelectrons ionized from xenon atoms and their dimers by using ultra-short strong laser are studied,due to the valu-able and insufficient studies on xenon dimers photoionization.The results show that a suppressed ionization is revealed in the energy regime where photoelectrons directly emit(<9.1 e V),when one compares the momentum distribution or kinetic energy distribution of photoelectrons derived from xenon dimers with that derived from xenon atoms.Ad-ditionally,the above suppressed ionization would be stable while laser intensity changes.The suppressed ionization regime can shift to the high-energy regime of photoelectrons,as laser intensity increases.In order to explain the above measured suppressed ionization,a theory of strong-field approximation for many electrons and atoms combining with ionic states is firstly built,and then a theory of two energy-level-based two-center quantum interference is built.It is indicated that the suppressed ionization of xenon dimers arises from two-center quantum interference.For xenon dimers,the kinetic energy distribution of photoelectrons exhibits the features mainly modulated by the interference term cos²(R·p/2).Meanwhile,the Xe₂⁺ions have large probability to populate at the spin-orbit-coupled I(1/2)_uground state,which is derived from the removal of an electron mainly from the?_uorbital.Therefore,whether the molecular spectra have a suppressed yield in the low energy range not only depends on the symmetry of HOMO molecular orbital but also depends on the properties of component atomic orbitals.Besides,two-center quantum interference can be influenced by the transition between eigenstates in superposed ionic state.For the clusters ionization,an additional particles migration could be exhibited,and thus migration can not find in molecular ionization.Since the strong-light-induced ioniza-tion of water cluster is significant,and the measured time scale of proton transfer is still lacking,the ionization processes of isolated water molecules and water dimers are studied.Based on the time-of-flight spectrum of first order ionization of water dimers,the water dimer cations(H₂O)₂⁺is proved to have a life with microsecond magnitude.For second order ionization,the protonated productions H₃O⁺and OH⁺and the unprotonated pro-ductions H₂O⁺are both detected in Coulomb explosion channel.The unexpected low proportion of protonated productions is attributed to the time delay of proton transfer.Finally,combing the measurements and the tunneling theory of strong field ionization,the time scale of fast proton transfer is obtained to be 31±5 fs.This result is well accordance with the result calculated by molecular dynamics.Different with the strong-light-induced ionization of microscopic system,the dense laser-induced plasma can be generated during the ionization of macroscopic continuum.In this dissertation,transient coupling equations of laser-induced plasma are built.By using this model,the evolutions of laser-induced plasma and laser field are calculated.Moreover,the calculated breakdown threshold and the calculated energy losses can agree with the experimental results quantitatively.The calculation results show that the generating plasma can move against the direction of laser propagation,and the velocity of this inverse movement can increase as the laser intensity increasing.Besides,the plasma expansion,the coupled optical field of plasma and the energy balance during plasma generation are also discussed.Compared with aqueous medium,there exists additional boundary in droplet.The water cloud consists of numerous droplets with different radii.By using the above tran-sient coupling model,the evolutions of the laser field and its self-generated plasma are calculated.Also the nonlinear absorption of droplets during optical breakdown is studied.It is shown that as each cloud droplet has both lens and cavity features,the droplet break-down threshold is only 1/6 th that of water.It is demonstrated that the laser-induced plasma evolution is independent for each cloud droplet.Meanwhile,the nonlinear ab-sorption threshold of water cloud is studied.If laser intensity is below this threshold,the laser energy is only slightly deposited in the water cloud,otherwise the energy deposit proportion increases largely with the laser intensity.We would expect that the researches in this dissertation could be helpful to the topics on strong field and attosecond physics,molecular structure detection,EUV laser,DNA functions,chemical reactions involved water,laser-induced plasma,laser ophthalmology,laser propagation in the air and laser-based weather controls.