The Study On Remote Sensing Of Hydrocarbon Molecules By Femtosecond Laser Pulses

In transparent media, high power femtosecond laser can produce a self-guidedstructure, called filament. In atmosphere, such femtosecond filament can be controlledfrom several kilometers away. Therefore, an ideal benefit can be offered by filamentto inspecting the pollution sources in atmosphere. At the same time, intensityclamping effect can cause the laser power in the filament to reach1013/cm2. Such highintensity canbreakany molecules in the pathway of filament. These excited fragmentsemitting characteristic fluorescence spectrum (fingerprint) can be used to detectvarious substances in chemical and biological areas. Femtosecond filament techniquehas so many advantages inremote sensing, however, individuals are still lack ofdetailed knowledge of these physiochemical reaction. The main contents in this thesiscenter on sensing hydrocarbon molecules by femtosecond laser filament inducedfluorescence technique. The main contents are listed as follows:To begin with, we use femtosecond filament to inspect a serial hydrocarbon moleculesincluding methane acid, ethyl alcohol, n-propanol, isopropanol, butanone, ethylacetate. By analysis of these characteristic spectra, we successfully recognize thesehydrocarbon molecules. Comparing with LIBS of long laser pulses, the femtosecondfilament induced characteristic spectra are very “clean”. These characteristic spectralines are mainly attributed to the neutral dissociation of parent molecules viasuperexcited states. In order to get a deep understanding of the interaction betweenhydrocarbon and femtosecond filament and analysis these processes in detail, webuild up a coincidence momentum imaging system.Therefore, in the second part of this thesis, we mainly focus on building up thecoincidence momentum imaging system.The mission includes two parts: hardwareand software. In hardware part, we assemble and operate the ultrahigh vacuum chamber, connect and debug the following signal processing units (such as FAMP8,ATR19, CFD8b), assemble and debug the data acquiring system. In software part, webuild up the acquiring order in TDC8HP and data processing program. Using the CMIsystem we build, we obtain the time-of-flight mass spectroscopy of backgroundmolecules in high vacuum chamber and images of molecules dissociation.In the end, we summarize the accomplishments in this thesis and discuss the futurework.