Optical control of molecular dynamics: Molecular cannons, reflectrons, and wave-packet focusers

Abstract

We consider the control of molecular dynamics using tailored light fields, based on a phase space theory of control Ty. J. Yan ef al., J. Phys. Chem. 97, 2320 (1993)]. This theory enables us to calculate, in the weak field (one-photon) limit, the globally optimal light field that produces the best overlap for a given phase space target. We present as an illustrative example the use of quantum control to overcome the natural tendency of quantum wave packets to delocalize on excited state potential energy curves. Three cases are studied: (i) a "molecular cannon" in which we focus an outgoing continuum wave packet of I2 in both position and momentum, (ii) a "reflectron" in which we focus an incoming bound wave packet of I,, and (iii) the focusing of a bound wave packet of Na, at a turning point on the excited state potential using multiple light pulses to create a localized wave packet with zero momentum. For each case, we compute the globally optimal light field and also how well the wave packet produced by this light field achieves the desired target. These globally optimal fields are quite simple and robust. While our theory provides the globally optimal light field in the linear, weak field regime, experiment can in reality only provide a restricted universe of possible light fields. We therefore also consider the control of molecular quantum dynamics using light fields restricted to a parametrized functional form which spans a set of fields that can be experimentally realized. We fit the globally optimal electric field with a functional form consisting of a superposition of subpulses with variable parameters of amplitude, center time, center frequency, temporal width, relative phase, and linear and quadratic chirp. The best fit light fields produce excellent quantum control and are within the range of experimental possibility. We discuss relevant experiments such as ultrafast spectroscopy and ultrafast electron and x-ray diffraction which can in principle detect these focused wave packets.

Resolution of strongly competitive product channels with optimal dynamic discrimination: Application to flavins

“…Hence, for the situation in which wavepacket localization is desirable [ Fig. 13(b)], an initial launch composed of lower-energy eigenstates instills a "reflectron" character 59,60 on to the generated wavepacket, whereupon it is constructively amplified when returning to the Franck-Condon region. Conversely, an initial launch of higher-energy vibrational eigenstates imparts a "cannon" character 59,60 on to the outgoing wavepacket, which results in slightly degraded localization upon returning to the Franck-Condon window.…”

“…13(b)], an initial launch composed of lower-energy eigenstates instills a "reflectron" character 59,60 on to the generated wavepacket, whereupon it is constructively amplified when returning to the Franck-Condon region. Conversely, an initial launch of higher-energy vibrational eigenstates imparts a "cannon" character 59,60 on to the outgoing wavepacket, which results in slightly degraded localization upon returning to the Franck-Condon window. It is also possible that the observed chirp structure is a result of phase-only modulation, and various other structures, including replica double pulses with the appropriate intrapulse phase relation, would be obtained if amplitude modulation was included in the optimization routine.…”

A single isolated sub-50 attosecond pulse generation with a two-color laser field by a frequency-chirping technique

“…Frequency-chirping, i.e., a time-dependent change in the laser frequency during the pulse provides a new and easy way to create and control a focused wavepacket of the laser field [16][17][18]. It is usually easier to induce a chirping into a femtosecond pulse than to obtain a specific pulse shape.…”

Adiabatic Passage in a Three-State System with Non-Markovian Relaxation: The Role of Excited-State Absorption and Two-Exciton Processes

“…The possibility of the optical control of molecular dynamics using properly tailored pulses has been the subject of intensive studies in the last few years [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23]. Chirped pulses can selectively excite coherent wave packet motion either on the ground electronic potential energy surface of a molecule or on the excited electronic potential energy surface due to the intrapulse pump-dump process [1,5,11,12].…”