Controlling strong-field dynamics
with synthetic CEP-stabilized pulses
Wendell T. Hill, III
University of Maryland, College
Park, Maryland, 20742 USA
Strong-field dynamics has been
shown to be sensitive to the carrier-envelop phase (CEP). Experiments
with CEP-stabilized pulses, however, have been limited to few-cycle pulses ( 2
or 3 cycles). This is because the more cycles a pulse has, the less
sensitive experiments are to variations of the CEP. Recently, we
introduced a new approach we call synthetic CEP stabilization. Synthetic
CEP stabilization is possible with pulses containing a pair of peaks, but the
relative phase and temporal separation must be controllable
independently. As we will show, the first peak induces coherence in an
incoherent, isolated quantum system allowing the second peak to interact with a
coherent, isolated quantum system. Even though neither peak is CEP
stabilized – the phases of the peaks vary randomly from shot to shot – we are
able to observe phase effects even with pulses as long as 50 fs (20+ cycles)
because there is always a well-defined phase between the two peaks – synthetic
CEP stabilization. To demonstrate the power and utility of our approach,
we have investigated strong-field optimal control of molecular dynamics.
Three distinct processes concomitant with strong-field enhanced ionization were
studied as the CEP was varied: (i) the propensity for large amplitude
bending vibration of a nominally linear 3-atom system, (ii) the alteration of
the explosion strength and (iii) the modification of the branching ratios into
degenerate channels. We will present evidence suggesting the relative phase,
which has garnered little attention in optimal control literature, plays a much
more fundamental role in optimal control than previously thought. Our
results shed light on why closed-loop optimal control searches (e.g., genetic
algorithms) lead to multiple solutions with nearly the same efficiency.
Specifics of our results and their ramification will be presented.
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