Phase-locked ultra-broadband supercontinuum generation in a mid-infrared polarization gating.

We theoretically investigate the UV-assisted high-order harmonic generation (HHG) process in a mid-infrared polarization gating (PG) field. The ionization and recombination steps of the HHG process can be controlled simultaneously by the UV and PG pulses. The influences of the delay between the UV and PG pulses on the phase-locking degree and the intensity of the harmonics are presented quantitatively. The results show that the harmonics are phase-locked as well as the intensity is significantly enhanced by 3 or 4 orders at a proper delay. Then a phase-locked ultra-broadband supercontinuum with a bandwidth of 240 eV is produced efficiently, supporting the generation of a Fourier-transform-limited pulse duration below one atomic unit of time. In addition, efficient isolated 110 as pulses with tunable central wavelengths can be obtained directly by selecting a different range of the supercontinuum. [ABSTRACT FROM AUTHOR]