| Femtosecond filamentation could provide powerful research tools and potential applications for atomic and molecular physics, precision spectroscopy, laser chemistry and laser biological fields. Ultraviolet filamentation had some unusual characteristics, such as high single photon energy, excellent focusing feature, and gradually turned into a research hotspot of high power laser physics.Because of the enhancement of ultraviolet laser single pulse energy, and irregular distribution of light field, laser heterogeneously interacted with medium during transmission process, especially the emergence of multiple filamentation caused energy losses and filament collapse. The spatial modulation of light field improved irregular laser spot, and realized the control of filament.This thesis based on spatial modulation of interference effect of non-collinear ultraviolet femtosecond pulses, researched the control of filamentation effect. Our works were as follows:1,The research on spatial interference and light field modulation of double non-collinear ultraviolet femtosecond laser was studyed. When the wavelength of incident laser was confirmed, the coherent stripe narrowed slowly, and the number of stripe added, during the angle of two beams of coherent lights increased gradually. In addition, we found regular fringes emerged in the laser spot which was originally heterogeneous by interference effect of two non-collinear ultraviolet femtosecond laser pulses, and the aim of control filament process was achieved.2,The generation and observation of plasma grating by interference between two non-collinear interaction ultraviolet pulses was experimentally observed. After plasma grating generated by femtosecond ultraviolet coherent light field, we observed bright interference fringes via ion recombination through microscopic imaging. Comparing with single ultraviolet filament, the fluorescence intensity of plasma grating region got obvious enhancement, and it increased with the incident laser energy. In our experiments, the spectrum width of ultraviolet pulse increased by a factor of two compared to initial situation, i.e.4nm.3,The further enhancement of plasma grating by a following infrared pulse was observed. We imported infrared laser to plasma grating, and found the filament which generated by infrared laser interacted with plasma grating. When infrared laser and two ultraviolet coherent laser pulses synchronized, fluorescence intensity of interaction region enhanced significantly, almost was 8 times the fluorescence of plasma grating of non-collinear double ultraviolet beams of coherent light field. This demonstrated filamentation of infrared laser had a complementary effect on fluorescence of plasma grating. |
PDF Full Text Request