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Generation and Optimization of High-order Harmonics in the Interaction of Laser with N2O Molecule

Monfared, Mohammad | 2019

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 52519 (04)
  4. University: Sharif University of Technology
  5. Department: Physics
  6. Advisor(s): Sadighi-Bonabi, Rasoul; Irani, Elnaz
  7. Abstract:
  8. The X-ray attosecond pulses have many useful applications for studying atomic and sub-atomic scales phenomena in attosecond scale duration. Generation and optimization of high-order harmonics is an efficient way to produce such attosecond pulses which are studied in this thesis. There are several limitations in the attosecond pulse generation such as low efficiency of high-order harmonics, long duration of output pulses and the impossibility of producing an attosecond pulse with any desired wavelength in the x-ray region. Therefore, more investigations into high harmonic generation and fully control and optimization of this process is significant. In this thesis, high harmonic generation from nitrous oxide molecule is investigated and affecting factors are recognized. Then, by tuning the affecting factors such as chirp parameter and carrier-envelope phase of the driving laser field, the process of the high harmonic generation is optimized. The calculation is performed by using time-dependent density functional theory in the three-dimensional real space grid. A new semi-classical method for optimizing the process of high harmonic generation is introduced which is led to a significant enhancement of the harmonics yield and the cutoff frequency by 96% compared to the not optimized case. By optimizing high harmonics from N2O molecule, an isolated 25as pulse could be produced.Moreover, high harmonics from the bromine molecule is investigated in this thesis. The dynamical and structural minima appearing in the harmonic spectrum, the effect of the phase and polarization of the laser on the harmonic spectrum from bromine molecule has been investigated. The obtained result shows a dip in its high harmonic spectrum. It is demonstrated that this dip is a structural minimum and disappears by changing the polarization angle. Our investigations indicated that by applying a driving laser pulse with zero carrier-envelope phase and polarization angle of 30 degree relative to the molecular axis, the most efficient high harmonics from the bromine molecule is achieved
  9. Keywords:
  10. High Harmonics Generation ; Attosecond Pulse ; Time Dependent Density Functional Theory ; Nitrous Oxide ; Bromine Molecule ; X-Ray Laser

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