Comparative Study Of Characteristics Between Ultraviolet And Near-infrared Ultrafast Laser Induced Plasma Channel

Over the years, the propagation of femtosecond filament in transparent media has attracted considerable attentions. Filamentation in the near-infrared (IR) femtosecond pulse has achieved numerous excellent results, such as the generation of super-continuum from ultraviolet (UV) to IR, multiphoton ionization and conical emission, etc. the pulse self-compression due to filamentation provides the possibility for generation of few-cycle pulse. The UV femtosecond laser pulse has numerous outstanding optical features, such as excellent focus ability, high single photon energy, large ionization rate, and so forth. It is nevertheless somehow difficult to generate high-intensity UV fs pulses, and due to the lack of suitable UV fs sources, researches on UV femtosecond filaments are not as prevailing as those on near-IR filaments.In this thesis, the characterics of spectra, length, filamentation position, diameter, energy transmission and threshold by mJ-level UV femtosecond laser pulse are demonstrated. Compared to the properties of IR femtosecond filamentation, the potential values for developing the strong UV laser pulse are proposed. The main aim of this paper is to provide valuable data for the plasma spectroscopy of ultrafast UV laser.This thesis consists of three parts:1. An approach of frequency doubling-compensation-tripling in collinear structure for femtosecond pulses was designed and employed to fulfill efficient harmonic conversion,optimized the phase and group velocity mismatch and improves the conversion efficiency of third frnquency harmonic, so as to get the level of 10%. We realized the third frequency harmonic of mj and produced the peak power of 10GW lever. This provides the prerequisite for the study of ultrafast UV plasma filaments.2. We focused on the plasma filaments properties of UV in different focal length, such as the spectral change, length,position,diameter, energy change and threshold of plasma filaments,and got into the important parameters of threshold condition.3. The thesis measured characteristics of near-infrared plasma filaments, then make a comparative analysis about UV and infrared plasma filaments. Through experiment we have concluded the following conclusion:the VU and near-infrared plasma filaments have shown that Spectrum broadening effect; The self-focusing threshold of UV pulse is one order of magnitude lower than that of IR pulse. The focusing ability of UV pulse is more excellent than IR. The filaments length of UV pulse is longer than IR.