Physics @ Berkeley
Events in Physics
Title: 290F Atomic Physics Seminar    (Seminar)
Start Date: 02/08/2006
End Date: 02/08/2006
Time: 11:00 am
Location: 375 Le Conte Hall
Speaker: Ursula Keller
Affiliation: Zurich, Switzerland
Contact Person: Daniel W. Tatum   (510) 643-4906

"Intense CEO-controlled pulse generation and coherent control in the XUV regime using attosecond pulse trains."



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.