Characterization of attosecond harmonic pulses using the RABITT method = RABITT 방법을 이용한 아토초 고차 조화파 펄스의 측정

Interaction of atoms in an intense femtosecond laser results in high-order harmonic generation, a highly nonlinear process. The process is described well by the semi-classical three step model consisting of ionization, acceleration, and recombination. High-order harmonics have features needed for attosecond pulse generation such as broad bandwidth and equally spaced frequencies. The temporal profile of the attosecond pulse needs to be characterized in order to explore dynamics of atoms and molecules. An attosecond pulse train was generated from high-order harmonics obtained by focusing 25-fs, 0.8-mJ titanium sapphire laser pulses on argon gas. The attosecond pulse can be temporally characterized using the interference of two-photon transitions between the harmonics and time-delayed laser pulses, which is called the RABITT (reconstruction of attosecond beating by interference of two-photon transition) technique. The interference generates sidebands appearing between adjacent harmonics. The sideband intensity varies with time delay, from which the spectral phase information can be obtained. The attosecond pulse train can be reconstructed in the time domain from this information. The result confirms that the attosecond pulse repeats every half-cycle of the laser and has positive chirp. The duration of attosecond pulse is estimated to be 235 as, and the group delay dispersion is estimated to be $1.47e \times 10^{-32} s^2$. In conclusion, the temporal characteristics of attosecond pulse train are obtained successfully using RABITT, which will accelerate applications of attosecond pulses to ultra-fast phenomena.
Nam, Chang-Heeresearcher남창희researcher
Issue Date
259999/325007  / 020043952

학위논문(석사) - 한국과학기술원 : 물리학과, 2006.8, [ vi, 43 p. ]


RABITT; attosecond pulse; 고차 조화파; high-order harmonics; 아토초 펄스; 래빗

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