Coherent Control Of Terahertz Radiation From Two Color Pulses

Terahertz(THz)radiation from two-color laser-induced plasma has been extensively studied,due to its broad-bandwidth and high efficiency.Two color laser field is an effective way to coherently control the ultrafast phenomenon in strong-field physics.In this thesis,we investigate the mechanism of THz generation from two-color laser-field,demonstrate that the optimal phase can be used to measure the value of the relative phase and propose a feasible scheme to enhance THz yield and to generate the circular-polarized THz radiation.We also study the optimal phase jump of high-order harmonic generation from argon near the Cooper minimum(CM).The major results of this thesis are outlined as following:1.The optimal phase of THz generated from two-color laser-field is 0.8 π,when the intensity of the fundamental laser is set from 0.8×1014W/cm2 to 1.8×1014W/cm2 and the ratio of second harmonic to fundamental is below 25%.We experimentally prove the optimal phase of THz is robust enough to measure in situ the value of the relative phase in two-color field,establish a one-to-one mapping between the local phase slip induced by Gouy phase and the spatial position.The result is of critical importance for the investigation of far field THz radiation.We elucidate the role of the Gouy shift in the temporal reshaping.2.We investigate the intensity dependence of THz emission on the polarization of two-color laser pulses,and demonstrate the circularly-polarized two-color pulses with the same helicity contribute to THz yield more efficiently than the linearlypolarized two-color pulses.The maximal enhancement factor is 5 for a single atom and 7 for air plasma.3.We investigate the coherent polarization control of THz radiation generated from two-color laser field.The arbitrary polarized THz is generated by breaking the antisymmetric phase distribution induced by Gouy phase,by controlling the length of the filament or by using the nonharmonic two-color field.The maximal ellipticity is about 0.9.4.We have experimentally studied the CM in the high-harmonic spectrum generated in argon with the help of the optimal phase of THz.The results show the phasematching conditions will be influenced by CM.