光电子成像方法研究N_2多光子电离过程

Multiphoton Ionization Process of Nitrogen Investiged by Photoelectron Imaging Method

利用速度映像成像技术实验探测了N2在70 fs,410 nm,场强(1-3)×1014W/cm2范围内的光电子成像,获得了光电子的动能分布和角分布.研究表明分子强场电离有一些和原子相似的性质.电子产生于两步过程,中间态有真实布居.在低场强非共振布居转移起主要作用,在较高场强共振布居转移起主要作用.光电子角分布体现中间态的角量子数特征.

Femtosecond multiphoton ionization dynamics of N2 is studied by using velocity map imaging technique and 70 fs laser at 410 nm from 1 to 3 × 10^14 W/cm2. The kinetic energy and angular distributions of photoelectron are measured and analyzed. The insensi- tivity of the photoelectron energy to peak laser intensities suggests that the electrons actually result from a two-step process, indicative of the occurrence of real population in the in- termediate states. The real population transfer consists of two parts：resonant population transfer at resonant intensity and nonresonant population transfer after resonant excitation during the pulse. The relative amplitudes of electron peaks at different peak laser intensi- ties indicate that in the two-step process, nonresonant population transfer dominates for low intensities, while resonant population transfer dominates for higher intensities. Photoelectron angular distributions reflect the character of the intermediate state.