Wavepacket-shaping by a frequency-chirping technique

Analytical optimal pulse shapes obtained with the aid of genetic algorithms

We propose a methodology to design optimal pulses for achieving quantum optimal control on molecular systems. Our approach constrains pulse shapes to linear combinations of a fixed number of experimentally relevant pulse functions. Quantum optimal control is obtained by maximizing a multi-target fitness function using genetic algorithms. As a first application of the methodology, we generated an optimal pulse that successfully maximized the yield on a selected dissociation channel of a diatomic molecule. Our pulse is obtained as a linear combination of linearly chirped pulse functions. Data recorded along the evolution of the genetic algorithm contained important information regarding the interplay between radiative and diabatic processes. We performed a principal component analysis on these data to retrieve the most relevant processes along the optimal path. Our proposed methodology could be useful for performing quantum optimal control on more complex systems by employing a wider variety of pulse shape functions.

QUANTUM WAVE-PACKET EXPLORATION OF ISOLATED ULTRA-SHORT ATTOSECOND PULSE GENERATION BY A MODIFIED THREE-COLOR LASER FIELD SCHEME

By numerically solving the three dimensional time-dependent Schrödinger equation, we explore the high-order harmonic and attosecond pulse generation of He atoms exposed to a special three-color field. An ultrabroad supercontinuum with a bandwidth of 887 eV has been attained, supporting an isolated 4 as pulse straightforwardly by Fourier transforming. Utilizing available intense infrared femtosecond laser resource within the nonrelativistic regime, the produced laser pulse is near to zeptosecond region. Remarkably, the harmonic conversion efficiency is enhanced in terms of the double-plateau structure of the harmonic spectra, yielding high-intensity attosecond pulses with alternative plateau.

A THEORETICAL ANALYSIS OF THE DISSOCIATION OF OH RADICAL: FINE-STRUCTURE DISTRIBUTIONS OF THE O(3PJ) PRODUCT

A theoretical treatment is presented for the nonadiabatic photodissociation of hydroxyl radical. Five electronic states, X 2Π, A 2Σ+, 14Σ-, 12Σ- and 14Π, are included in this simulation. Based on the accurate ab initio calculations of the potential energy curves, transition dipole moments and nonadiabatic couplings between the relevant states, the dissociation dynamics are investigated using the time-dependent quantum wave packet approach. The direct dissociation, following the excitation from the specific vibrational levels of the ground state X 2Π to the repulsive state 12Σ- is examined, where the total and partial cross sections and the branching fractions of spin–orbit fine-structures of O (3 P J) are calculated over a wide range of the incident photon frequencies. For the predissociation via the bound excited state A 2Σ+, the influence of the nonadiabatic interactions in different internuclear regions and the role of the repulsive states in the dissociation starting at different vibrational levels are also analyzed through the spin–orbit branching fractions of products.

SELECTIVE EXCITATION OF HIGH VIBRATIONAL STATES OF HYDROGEN FLUORIDE IN A THERMAL ENVIRONMENT BY ULTRAFAST INFRARED LASER PULSES

The selective excitation of the high ground vibrational state of rotationless HF in an unobserved quasi-resonant thermal environment under the control of a single pulse and pulse train is studied using the reduced density matrix theory. It is shown that the pulse train can enhance the population transfer probability. The numerical results reveal that the vibrational relaxation process is affected by the distribution of the environment frequency and the molecule–environment coupling intensity. The effects of the molecule–environment coupling parameter and the overlapping pulses on the population of the target state of HF are also discussed.

MODEL REAL-TIME QUANTUM DYNAMICAL SIMULATIONS OF PROTON TRANSFER IN THE GREEN FLUORESCENT PROTEIN (GFP)

In this paper, we present the results from model real-time quantum dynamical calculations of the proton transfer in green fluorescent protein (GFP) regarding four electronic states (labeled A, A*, I, I*). A coupled-states quantum wavepacket method has been used, which involves split-operator and fast FFT algorithms. The model potential energy surfaces are based upon data derived from experimental results with some modifications. Several important processes in GFP have been simulated, which include the photo-absorption and proton transfer in the excited state, the isotope effect and the recurrence time for proton motion in the excited state. The origin of the early-time (prompt) stimulated emission is tentatively explained in terms of off-resonance excitation as well as the contribution from the fastest component for proton transfer in GFP.

Theoretical study of the photodissociation of Li(2)+ in one-color intense laser fields

A theoretical treatment of the photodissociation of the molecular ion Li(2) (+) in one-color intense laser fields, using the time-dependent wave packet approach in a Floquet Born-Oppenheimer representation, is presented. Six electronic states 1,2 (2)Σ(g)(+), 1,2 (2)Σ(u)(+), 1 (2)Π(g), and 1 (2)Π(u) are of relevance in this simulation and have been included. The dependences of the fragmental dissociation probabilities and kinetic energy release (KER) spectra on pulse width, peak intensity, polarization angle, wavelength, and initial vibrational level are analyzed to interpret the influence of control parameters of the external field. Three main dissociation channels, 1 (2)Σ(g)(+) (m = -1), 2 (2)Σ(g)(+) (m = -2), and 2 (2)Σ(u)(+) (m = -3), are seen to dominate the dissociation processes under a wide variety of laser conditions and give rise to well separated groups of KER features. Different dissociation mechanisms for the involved Floquet channels are discussed.