Experimental Study On Coulomb Explosion And Angular Distribution Of Nitrogen Molecules In Femtosecond Laser Field

With the development of ultra-fast and ultra-short laser technology,the interaction between femtosecond laser and molecules has aroused people's great attention.The fundamental process of the interaction between femtosecond laser and molecules is electronic ionization and the ionization process is great important research distribution for strong field physics.When the process of multiple ionization occurs,due to the coulomb force of molecular ions,the molecular ions dissociate into different ion fragments with kinetic energy release?KER?.The information on ion charge state,KER and angle distribution can be obtained by the time of flight-mass spectra?TOF-MS?.Further,the information may provide important experimental data for people to study femtosecond laser interaction with molecular mechanism and process.In this dissertation,the ionization and dissociation process are studied by a home-built ultra-high vacuum TOF and combine special extraction-acceleration electrodes and momentum and energy conservation law to select specific molecular ion pair from disorderly coulomb explosion.1.Based on classical mechanics and Monte Carlo methods,we write a set of simulation program about the process of ions flying and simulate the ion transportation in TOF-MS.According to this program,we optimize the extraction-acceleration electrodes.The extraction-acceleration electrodes can limit lots of coulomb explosion ion pairs with large angle and select specific molecular ion pair.2.We redesign a set of MCP detector.The signal trailing and oscillation are eliminated by improving power supply and collection circuits.3.According to momentum and energy conservation law,the selected ion pairs are identified one by one.Different dissociation channels and their KER are accurately identified.The KERs measured at laser intensities varying from 4×1014W ? cm² to 2×1015W ? cm² are found to stay constant.4.The angular distributions are measured at laser intensity of 9×1014W ? cm².With good exclusion of other ions,there is an elusive shrink structure at ? = 0°and the elusive structure is mainly derived from coulomb explosion of different states of N₂²⁺.