"Intense CEO-controlled pulse generation and coherent control in the XUV regime using attosecond pulse trains."
Ursula Keller
ETH Zurich, Switzerland
Wednesday, February 8, 2006 from 11- 12:00 Noon in 375 LeConte Hall
Abstract
High harmonic generation opens the way towards attosecond pulse generation.
Single attosecond pulse generation requires not only intense, reproducible few-cycle
drive pulses, but also a control of the carrier phase with respect to the pulse
envelope (i.e. the carrier envelope offset, CEO). Until recently the only
successful demonstration of CEO-phase-locked intense pulses was based on a CEO
stabilized Ti:sapphire laser, chirped-pulse amplification and pulse compression in
a hollow fiber. Meanwhile, there are some new promising ways to achieve this goal.
One is based on chirped pulse optical parametric amplification (CPOPA) and the
other on pulse compression through filamentation.
During this talk CEO-controlled filament self-compression will be reviewed which
resulted in pulse durations as short as 5.1 fs to date.
For longer IR pulses attosecond pulse trains (APTs) are generated. During this
talk we discuss the possibility for coherent control of high-order harmonic
generation using APTs. Here the APTs are being used as a tool for controlling
strong field processes in high-order harmonic generation. When used in combination
with an intense infrared laser field, the timing of the APT with respect to the
infrared (IR) laser field can be used to microscopically select a single quantum
path contribution to a process that would otherwise consist of many interfering
components. It is through this timing that we predict control over the release of
the electron into the continuum, its excursion inside the continuum and consequently influence the yield and coherence of the harmonics. Macroscopic propagation effects
in the APT assisted harmonics generation predicts a much larger enhancement than
by the simple single atom model alone. This is a volume effect, because the
enhancement is much larger at the lower IR intensity. In a first experiment we
have generated extreme ultraviolet (XUV) harmonics around 90 eV in He using a
combination of vacuum ultraviolet (VUV) harmonics, generated in a Xe capillary,
and the strong infrared (IR) laser pulse. With no changes in the IR input energy
or the configuration of the He target, the collinearly focused combination of the
two fields changed the spectral properties and increased the yield of the XUV
harmonics compared to those generated with the IR field alone.
