Research On Mechanisms For Generation Of Mid-infrared Driven Laser Source And Attosecond Pulse

The birth of attosecond pulse brings a ultrafast measurement tool with unprecedented resolution for humanity, and opens the door for attosecond science. In a few short years, the attosecond pulse has obtained a series of excited achievements in atomic and molecular physics, nano-materials, condensed materials, and so forth. The key for further application of attosecond pulse is to generate the attosecond pulse with shorter duration, shorter wavelength and higher intensity. In this dissertation, we systematically study the new mechanisms for the generation of attosecond pulse based on high-order harmonic radiation. Because of the desire for the high-power mid-infrared laser source to generate the intense and ultrashort attosecond pulse, the generation of high-power mid-infrared source is also investigated. The main contents of our work are described as follows.The high-order harmonic radiation driven by a two-color laser field is investigated. By mixing a sub-harmonic control field to the fundamental field, the electron dynamics can be efficiently controlled and the bandwidth of supercontinuum can be broadened. By adjusting the relative phase between the fundamental field and control field, the selection of quantum path can be realized. Therefore, the two-color driven scheme with well-chosen parameters is an efficient way to generate the broadband single attosecond pulse.The high-order harmonic generation from stretched molecules is investigated. The cut-off of high-order harmonic spectrum can be extended to Ip+8Up with a proper internuclear distance. Besides the harmonic radiations beyond Ip+3.17Up contributed by the long and short trajectories are synchronized. Employing a two-color laser field as driven pulse, the bandwidth of high-energy harmonic spectrum which can be utilized to produce single attosecond pulse is broadened but also the efficiency of high-energy harmonic spectrum is improved, therefore the broadband single attosecond is generated.The high-order harmonic generation from asymmetric molecules is investigated with the polarization gating method. An obvious asymmetry in high-order harmonic yields is observed when the asymmetric molecules are rotated by 180°due to the asymmetric potential well. This implies that the harmonic radiation within one half optical cycles can be extracted by polarization gating method; therefore the asymmetric structure of the molecules will be reflected on the harmonic spectrum, which will pave the way for tomographic imaging of asymmetric molecular orbitals. Furthermore, the shortest pulse duration we can be used for generating broadband single attosecond in asymmetric molecules is twice as long as that for applying polarization gating method to atoms due to the periodicity of harmonic radiation is broken down.The mid-infrared modulated polarization gating method is proposed for generation of single attosecond pulse. In this scheme, the driven pulse with longer wavelength is used for intensifying the dependence of harmonic efficiency on ellipticity and extending the plateau of harmonic spectrum, combined with the ionization modulation induced by second-harmonic control field, not only the broadband single attosecond pulse can be generated in the extreme ultraviolet region but also the available driven pulse duration is increased to 8 optical cycles. The availability of multi-cycle driven pulse for producing single attosecond pulse significantly looses the requirement of laser system in experiment.A high-power mid-infrared laser source employing dual-chirped optical parametric amplification scheme based on Ti:sapphire laser system is proposed. By chirping both pump and seed pulses in an optimized way, high-energy pump pulses can be utilized, and broadband signal and idler pulses with a total conversion efficiency approaching 40% can be generated. In addition, idler pulses with a passively stabilized carrier-envelope phase can be generated by the difference frequency generation process. We believe that this scheme has great potential to markedly increase the mid-infrared pulse energy, which will pave the way for the generation and application of not only intense ultrafast coherent extreme ultraviolet X ray but also high-intensity laser physics.