Generation of isolated ultra-short attosecond pulses by coherent control of the population of excited states

作者：Jooya, Hossein Z.^*; Li, Peng-Cheng; Liao, Sheng-Lun; Chu, Shih-I

来源：Physics Letters, Section A: General, Atomic and Solid State Physics , 2016, 380(1-2): 316-321.

DOI：10.1016/j.physleta.2015.09.040

• High-harmonic generation
• Attosecond pulse
• Coherent control

We present an ab-initio theoretical investigation of the enhancement of ultra-broad super-continuum harmonic spectra by coherently controlling the electron quantum paths of the helium atom and He+ ion. The time-dependent Schrodinger equation is solved by means of the time-dependent generalized pseudo-spectral method, allowing non-uniform and optimal spatial grid discretization and accurate and efficient propagation of the wave function in space and time. The population of the first two low-lying excited states of He+ is selectively controlled by adding low intensity, high frequency laser pulses to a two color mid-infrared laser field. Although the intensity of the added field is weak, its high frequency makes the subsequent ionization probability from excited states become much larger than for the case of many photons (mid-IR filed), even though the intensity is smaller. We found that the intensity of the attosecond pulse generated by superposing a range of synchronized high harmonics is significantly enhanced by 20 orders of magnitude. Similar calculations have been performed for the neutral He atoms. We found that an intense and ultra-short isolated 18 as can be generated directly. To understand the underlying mechanism of such dramatic enhancement and the role of electron quantum paths, we perform wavelet time-frequency transform of high harmonic spectra. The results show that we can selectively control the domination of the two distinct long and short electron trajectories by controlling the population of different excited states.

• 出版日期2016-1-8
• 单位西北师范大学