11 research outputs found
Monotonically convergent optimal control theory of quantum systems under a nonlinear interaction with the control field
We consider the optimal control of quantum systems interacting non-linearly
with an electromagnetic field. We propose new monotonically convergent
algorithms to solve the optimal equations. The monotonic behavior of the
algorithm is ensured by a non-standard choice of the cost which is not
quadratic in the field. These algorithms can be constructed for pure and
mixed-state quantum systems. The efficiency of the method is shown numerically
on molecular orientation with a non-linearity of order 3 in the field.
Discretizing the amplitude and the phase of the Fourier transform of the
optimal field, we show that the optimal solution can be well-approximated by
pulses that could be implemented experimentally.Comment: 24 pages, 11 figure
Monotonically convergent optimal control theory of quantum systems with spectral constraints on the control field
We propose a new monotonically convergent algorithm which can enforce
spectral constraints on the control field (and extends to arbitrary filters).
The procedure differs from standard algorithms in that at each iteration the
control field is taken as a linear combination of the control field (computed
by the standard algorithm) and the filtered field. The parameter of the linear
combination is chosen to respect the monotonic behavior of the algorithm and to
be as close to the filtered field as possible. We test the efficiency of this
method on molecular alignment. Using band-pass filters, we show how to select
particular rotational transitions to reach high alignment efficiency. We also
consider spectral constraints corresponding to experimental conditions using
pulse shaping techniques. We determine an optimal solution that could be
implemented experimentally with this technique.Comment: 16 pages, 4 figures. To appear in Physical Review
Field-free molecular orientation by nonresonant and quasiresonant two-color laser pulses
International audienceWe analyze the control of molecular orientation by nonresonant and quasiresonant two-color laser pulses (2+1 process). The laser pulses are assumed to be short with respect to the rotational period. In the nonresonant case, we show that the efficiency of this strategy crucially depends on the polarizability and the hyperpolarizability of the molecule. In the quasiresonant case, i.e., if the 2ω frequency is in quasiresonance with a vibrational frequency, one can improve the orientation by adjusting the detuning. The best orientation is obtained for an optimal value of the detuning, which is different from zero
Snapshot imaging of postpulse transient molecular alignment revivals
International audienceLaser induced field-free alignment of linear molecules is investigated by using a single-shot spatial imaging technique. The measurements are achieved by femtosecond time-resolved optical polarigraphy FTOP . Individual alignment revivals recorded at high resolution in CO2, as well as simultaneous observation of several alignment revivals produced within the rotational period of the O2 molecule are reported. The data are analyzed with a theoretical model describing the alignment experienced by each molecule standing within the interaction region observed by the detector. The temporal dynamics, intensity dependence, and degree of alignment are measured and compared with the awaited results. The technique is simple and can be easily implemented in a large class of molecular samples. Improvement to extend the performance of the method is discussed. The reported study is a decisive step toward feedback optimization and optimal control of field-free molecular alignment
Control and optimization of postpulse molecular alignment by shaped laser pulse
Talk given by O. FaucherInternational audienc