Dr. Ko Dong Hyuck
January 11(Thu) - January 11(Thu), 2018
12:30
R109, UQBF
We demonstrated holographic measurement of attosecond high harmonic pulses and a femtosecond laser pulse in order to characterize time-dependent optical fields. To achieve this, we introduce a weak laser field into the harmonic generation medium together with the strong driving laser field [1,2]. The weak laser field perturbs the trajectories of ionized electrons periodically, which are very sensitive while generating high harmonics. Since the periodic structure in the near-field dipole emissions implies cross-correlation between the attosecond pulse and the perturbing laser pulse, we can achieve temporal characterization by measuring the diffracted high harmonic radiations.
Since the far-field intensity distribution is insensitive to the near-field dipole emissions, we superposed a reference X-ray beam generated from another source [3]. The measured harmonic image shows dense fringes that originate from two-source interference. The rapid oscillation enables us to reconstruct the near-field dipole emissions by applying Fourier transform [4]. As a result, we determined the attosecond pulses, showing a pulse duration of 390 as, and the time-dependent electric field of the perturbing laser pulse from the retrieved near-field image [5]. The duration of the perturbing pulse that we obtain is consistent with the result achieved by a conventional FROG measurement.
The holographic pulse measurement method is a fast, robust and effective way to monitor attosecond pulses in soft X-ray region. Eventually, it will be a new technique to probe ultrafast strong-field dynamics in many materials.