Design of optimal infrared femtosecond laser pulses for the overtone excitation in acetylene Original Research Article

Optimal laser pulses in the femtosecond region are designed for a state selective excitation of infrared overtone vibrations in acetylene, for which an experiment is actually set up in our institute. To attack the preparation problem the moleculeʹs Hamiltonian is reduced to the IR-active modes, which are the twice degenerated cis-bending and the asymmetric CH-stretching mode. For distinct populations we compute the corresponding two-dimensional potential energy surface, dipole moments and eigenfunctions and then use optimal control theory strategies to calculate applicable laser pulses. These optimized pulses are analysed in the time and frequency domain. Ladder climbing is found to be the preferred mechanism for very efficient and highly selective overtone excitation. This mechanism is discussed in detail and a model for the observed transition frequency shift is presented.