The Key Technologies For Generation Of The Ultraviolet Femtosecond Laser Pulses

In recent years, with the development of chirp pulse amplifier (CPA) laser technique, the applications of femtosecond laser pulses in near-infrared have become increasingly popular. A number of researches have focused in strong field and ultrafast laser physics. For example, spectrum modulation for the generation of ultra-short pulse, plasma filaments control, high harmonic generation (HHG), and so forth.Compared to near-infrared, femtosecond laser pulses in ultraviolet have numerous outstanding optical features, such as excellent focus ability, high single photon energy, large ionization rate, and low filamentation threshold. Femtosecond ultraviolet laser pulses have more and more application in the generation of high intensity optics field, the development of high resolution imaging technology.To achieve ultraviolet femtosecond laser source with high power, broad bandwidth, as well as the high intensity in filament, three innovative research works consist of this thesis:1. The achievement of high power ultraviolet femtosecond laser pulse:This is the foundation of high power ultra short ultraviolet laser source generation. Three cascade BBO crystals were used as a technology of double frequency-compensation-sum frequency, and the energy conversion is above 7% of the fundamental wavelength. The output energy of the CPA system is 70mJ/70fs and was processing through three BBO crystals and the generated third harmonic generation pulse (THG) is about 5mJ.Because of self-clean in the filament, the beam profile is similar to Gaussian distribution.2. Spectrum broadening of the ultraviolet femtosecond pulse:is another one of the most important key technologies in the generation of few cycle ultraviolet femtosecond pulses. Molecular alignment was used to modify the THG spectrum, as the rotation level of the gas molecular was excited by fundamental femtosecond laser pulse, gas molecular was spatial periodically alignment as time revised. The spectrum bandwidth of the UV pulse is broadened to be about 6nm,9nm, and 13nm in nitrogen, oxygen and carbon dioxide, respectively. In theory, the sub-10 fs of pulse duration could be obtained in Fourier limit.3. Currently the manipulation of single filament as well as spatial modulation of electrical field is research focus. It is well known that the power intensity in filaments is clamped due to the balance between Kerr self-focusing and defocusing induced by plasma. In our experiments, a plasma grating is generated via the non-collinearly interaction between two temporally overlapped UV femtosecond filaments. As the crossing angle between these two filaments is tuned to be appropriate, a bright single filament is generated. In such case, the diameter of the filament is below the Fraunhofer diffraction (the diameter of the single filament is～5μm).