One of the most crucial issues for the present attophysics is to
increase the pulse energy of isolated attosecond pulses (IAP.s). For
this purpose, there are two crucial experimental challenges to
demonstrate; one is to develop multi-mJ few cycle lasers with a
stabilized carrier-envelope phase (CEP) and the other is to achieve the
phase-matching highly between the few cycle pulses and high harmonics of
them.
In this talk, I will present our research activities on both challenges.
First, I will present our recent results of RIKEN based on our
TW-class 2-cycle laser system (5 fs, 780 nm, 5 mJ, 1 kHz). Recently, we
have stabilized CEP of this system with two feedback loops and by
blocking mechanical vibrations on the laser system thoroughly. Through
the phase matching process, we could select the supercontinuum component
of the harmonics without any use of bandpass filters such as Mo/Si
mirrors. By using a heterodyne interferometry using mixed gases, we
verified that we could select IAP directly. Second, I will briefly
introduce our recent results at Imperial College London on constructing a
CEP-stabilized high power OPA (optical parametric amplification) laser.
CEP-stabilized seed pulses were generated using type II DFG of
different frequency components of the supercontinuum generated with a
hollow fiber compression technique, and the seed pulses were amplified
by two-stage OPA.s. Final output pulses had a pulse energy of 500 μJ,
pulse duration of 40fs, and tunable wavelength from 1300-1800 nm. As
the first demonstration of this handmade laser, we could generate high
harmonics up to 47th using a tube target filled with Xe gas.
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