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Coincident Measurement of High-order Harmonics and Terahertz Waves Generated by Ionizing Inert Gas in Two-color Fields

Author: DuXiYu
Tutor: ZhaoZengXiu；ZhangDongWen
School: National University of Defense Science and Technology
Course: Atomic and Molecular Physics
Keywords: Two-color fields High-order Harmonic Generation Terahertz Relative phase Coincident measurement
CLC: TN215
Type: Master's thesis
Year: 2011
Downloads: 35
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Abstract


The interaction between intense laser fields and atoms or molecules has been a hot topic for a long time. High-order harmonics and terahertz waves are both generated during ionizing of atoms and molecules in intense laser fields. When two-color fields are applied, the generation efficiency of high-order harmonics and THz both increased depending on the relative phase between the two-color fields. In this thesis, the dynamics linking high-order harmonic generation (HHG) and THz emission is investigated experimentally from inert gas atoms in intense two-color fields.The effect of the phase difference on the high-order harmonic spectrum of inert gases in the two-color field is studied firstly. In the experiment, the 800nm, 25fs, 1k Hz fundamental field and its second harmonic field are focused into the gas cell to ionize the atomic Ne or Ar to generate high-order harmonics. It’s found that weak even-order harmonics are generated and periodically modulated by the relative phase of the two fields when the second harmonic intensity is three orders lower than the fundamental laser intensity. Further increasing the intensity of the second harmonic, even-order harmonics get more intense, and reversed modulation is observed for odd-order harmonics. The modulation phase depends on the harmonic order. Theoretical calculation is performed by solving the time-dependent Schrodinger equation numerically, and the results agree well with the experimental observation. When the intensity of the second-harmonic is increased to 25% of the fundamental field, the odd-order and even-order harmonics start to be modulated in the same way. The high-order harmonics of atomic Ar in the cut-off region are studied using less intense two-color field, and the similar results are observed.HHG and THz waves generated by Ne and Ar in two-color fields are coincidently measured in this thesis. In the experiment, we found that in the cut-off region, the harmonics and THz waves are modulated out of phase, which agree well with the theoretical calculation.

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CLC: > Industrial Technology > Radio electronics, telecommunications technology > Photonics technology,laser technology > Infrared technology and equipment > Infrared detection,infrared detectors
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