We present an implementation of an additional cost in the functional of the recently published iteration methods for quantum optimal control [W. Zhu, J. Botina, and H. Rabitz, J. Chem. Phys. 108, 1953 (1998)] to design optimal laser pulses for population transfer. The additional criterion takes into account the asymptotic switch on and off behavior of experimentally generated laser pulses. Exemplarily, a specially adapted windowed Fourier transform is applied to decompose a complex, highly nonintuitive optimal laser field in a sequence of subpulses to provide laser pulse parameters as helpful information for experimental reconstruction. Numerical calculations for three typical spectroscopic excitation mechanisms show that laser fields obtained with the new functional signify a step towards experimental feasibility.
Isomerization reactions from a reactant state to a near-degenerate product state which are typical for
intramolecular hydrogen transfer may be achieved by means of ultrashort picosecond or sub-picosecond laser
pulses having three consecutive time domains. Initially, the laser field is switched on such that the wave
packet representing the reactant is converted into a superposition of near-degenerate delocalized states of the
“dressed” molecule, with level spacing ΔE
ε. In the second stage, the laser field ε is kept approximately
constant until the wave packet has tunneled from the reactant to the product configuration, during the tunneling
time τε = h/2ΔE
ε. Finally the field is switched off in such a way that the wave packet is stabilized as the
target product state. This approach is suggested by optimal control theory and applied to a one-dimensional
model resembling substituted malonaldehydes. Here it is found that the laser-driven tunneling requires time-integrated laser field intensities fifty times smaller than the alternative pump−dump approach which drives
the reactant wave packet over the potential barrier toward the product state without tunneling. Various
applications and extensions of this method are discussed.
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