THEORY OF ULTRAFAST LASER CONTROL FOR STATE-SELECTIVE DYNAMICS OF DIATOMIC-MOLECULES IN THE GROUND ELECTRONIC-STATE - VIBRATIONAL-EXCITATION, DISSOCIATION, SPATIAL SQUEEZING AND ASSOCIATION

An overview of the current state of the art in the laser control of mo lecular dynamics is presented with a special emphasis on the ultrafast vibrationally state-selective processes controlled by short and shape d infrared laser pulses. Ultrafast state-selective vibrational dynamic s and dissociation of isolated diatomic molecules in the electronic gr ound state under the control of intense and shaped infrared laser puls es of picosecond and femtosecond duration is investigated within the S chrodinger wavefunction formalism. The laser driven dissipative dynami cs is investigated within the reduced density matrix formalism beyond and within a Markov-type approximation for the ultrafast state-selecti ve excitation of diatomic molecules, which are coupled to an unobserve d quasi-resonant thermal environment. Quantum dynamics in a classical electric field is simulated for a one-dimensional Morse oscillator, re presenting the local OH bond of the H2O and HOD molecules in the elect ronic ground state. Flexible tools of optimal laser control are develo ped and demonstrated on a picosecond timescale, which enable to locali ze the population with a very high probability at any prescribed vibra tional level of OH, including those close to the dissociation threshol d, without substantial dissociation. Comparative analysis of the Marko vian and non-Markovian dissipative quantum dynamics reveals that the M arkov approximation results in a pronounced decrease of a predicted pr obability for ultrafast selective preparation of very high vibrational bound states. The laser-controlled dissociation from selectively prep ared high vibrational bound states is investigated for a wide range of the laser carrier frequencies, revealing the role of the phase of the dissociating laser pulse. In the limiting case of small laser frequen cies, for half-cycle pulses, a spatial squeezing of highly excited mol ecules is discovered. It is demonstrated that the optimally controlled dissociation may be very efficient, and the dissociation probability may approach the maximal value. Quantum dynamics of vibrationally stat e-selective association of a diatomic molecule in the electronic groun d state controlled by shaped sub-picosecond infrared laser pulse is in vestigated by means of representative wavepackets. It is shown, in par ticular, that a colliding pair of O and H atoms can be transferred sel ectively into a prespecified vibrational bound state of OH(v). Optimal design of the laser field controlling this process results in a high association probability with a very high vibrational state-selectivity . (C) 1997 Elsevier Science B.V.