Study Of The Coulomb Explosion Of Nitrogen Molecule Induced By Intense Femtosecond Laser With A High Resolution Time-of-flight Spectrometer

The gaseous molecules will be stripped a number of electrons when they interact with the femtosecond laser pulses, which leads to the generation of multicharged mother ions. Then the strong Coulomb repulsion power between the inner groups of the mother ions will cause the dissociation of the mother ions. And this process is named as the Coulomb Explosion(CE). As a simple but reliable instrument, the Time-of-Flight mass spectrometer is widely used by the researchers all over the world to study the Coulomb Explosion of the gaseous molecules and clusters. In order to study the Coulomb Explosion of Nitrogen molecules induced by the femtosecond laser pulses, we build a high resolution TOFms with the better Microchannel Plate Detector and more powerful data acquisition device.We have the following achievements after a lot of research work. First, the development of high resolution Time-of-Flight mass spectrometer provides a powerful tool for the further study of the interaction between the femtosecond laser and gas molecules. The resolution of the TOFms is about 2000, which can meet the requirements of our experiments. We improve the performance of the MCP detector by redesign its electric circuit. The pulse of the MCP detector has a shorter tail after it and its width is less the 2ns. In this way, we improve the resolution of the system a lot. We do a lot of efforts to improve the vacuum of the chamber and finally the vacuum is better than-84.0 ×10 Pa. We compare different data acquisition methods and we choose the ADQ412 as our data collect system. We also developed a program to analysis the data, so the TOFms could access to the ions released by the laser gas interaction fast and precise. Second, we analysis the pulses’ height of the MCP detector and we find that the height of the pulses are something random. Researchers can not distinguish the different ions just by the height of the pulses. Finally, under the help of the covariance-mapping, we can distinguish different coulomb explosion pathways and we also calculate the kinetic energy releases of the different pathways.There are five chapters in this thesis. The first chapter is the introduction. In this part, we will introduce the development of the laser technology, the history of the TOFms and the research purpose of this thesis. In the second chapter, we will introduce the design of the TOFms, the femtosecond laser system, the microchannel plate detector(MCP), the vacuum acquisition devices and the Mc Laren accelerate region. The third chapter is about the data analysis system of the TOFms. We test the TOFms system and do a lot of work to improve the resolution of it. In the fourth chapter, we use the TOFms to study the femtosecond laser interaction with gas molecules. We will talk about the ionization mechanisms of the molecules and then study the Coulomb Explosion of the N2 molecules. Under the help of the Covariance-mapping, We can discriminate the different CE pathway even when the peaks on the TOF spectrum are ambiguous. After that, we calculate the kinetic energy releases of different pathways. The last chapter is a summary and we will describe the future use of the TOFms.