Generation of XUV supercontinuum and attosecond pulses
by half-cycle gating
J. R. Macdonald Laboratory, Kansas State University,
Manhattan, KS 66506, USA
Singe attosecond pulses at the cutoff region of high-order
harmonic spectra have been generated using few-cycle laser pulses.
We report a unique method that used birefringence optics to create a laser
pulse whose polarization varied rapidly from circular to linear and back
to circular, in order to produce single attosecond pulses over the much
broader plateau spectrum region. When a 8 fs pulse centered at 850 nm was
split and delayed with a quartz plate, then recombined with a quarter waveplate,
the near-linearly polarized portion of the resultant pulse was only 1.3
fs long that was much shorter than the laser pulse duration. The ellipticity
dependent pulse behaved like a half-cycle linearly polarized pulse for
generating high-order harmonics that is susceptible to ellipticity. By exciting argon gas with the pulse, a supercontinuum that covered 25
to 45 nm was produced in the plateau and cutoff region of high harmonic
spectrum, which corresponds to an estimated single 200 attosecond pulse.
The synchrotron like XUV spectrum is very important for time-resolved absorption
spectroscopy and for feeding x-ray FEL.