Molecular isomerization induced by ultrashort infrared pulses. I. Few-cycle to sub-one-cycle Gaussian pulses and the role of the carrier-envelope phase

Abstract

Using 550 previously calculated vibrational energy levels and dipole moments we performed simulations of the HCN-->HNC isomerization dynamics induced by sub-one-cycle and few-cycle IR pulses, which we represent as Gaussian pulses with 0.25-2 optical cycles in the pulse width. Starting from vibrationally pre-excited states, isomerization probabilities of up to 50% are obtained for optimized pulses. With decreasing number of optical cycles a strong dependence on the carrier-envelope phase (CEP) emerges. Although the optimized pulse parameters change significantly with the number of optical cycles, the distortion by the Gaussian envelope produces nearly equal fields, with a positive lobe followed by a negative one. The positions and areas of the lobes are also almost unchanged, irrespective of the number of cycles in the half-width. Isomerization proceeds via a pump-dumplike mechanism induced by the sequential lobes. The first lobe prepares a wave packet incorporating many delocalized states above the barrier. It is the motion of this wave packet across the barrier, which determines the timing of the pump and dump lobes. The role of the pulse parameters, and in particular of the CEP, is to produce the correct lobe sequence, size and timing within a continuous pulse.

Rotational averaging and optimization of laser-induced population transfer in molecules

“…In numerical simulations one frequently uses a model in which it is assumed that the orientation of the molecule is fixed or "clamped" with respect to the direction of the ͑linearly polarized͒ field throughout the interaction time. [1][2][3][4][5][6][7][8][9] In their review on stateselective dynamics, 1 Korolkov et al conclude that "more advanced model investigations" should include molecular rotation. In fact, free molecules do rotate and are statistically distributed over the quantum rotational states, and even in the condensed phases they may have a random orientation.…”

Calculation of the probability of photoprocesses induced by ultrashort electromagnetic pulses

“…A characteristic feature of the ultrashort laser action is that the probability of excitation of a quantum system depends on the relative phase between the carrier frequency and the pulse envelope (CE phase). Controlling the CE phase makes it possible to control various photoinduced processes, such as external photoeffect [3], molecular isomerization [4], photodissociation of molecules [5], generation of high harmonics [6], and some others. Besides, ultrashort pulses with a controllable CE phase allow one to obtain detailed information on the dynamics of excitation of atoms in the superthreshold ionization mode [7].…”

Geometrical Optimization Approach to Isomerization: Models and Limitations

“…-18]. Numerical results using N-level Hamiltonians under long pulses and wave-packet calculations in reduced (1 or 2)-dimensional models for short pulse dynamics have also shown great promise in the possibility of driving isomerization reactions [19][20][21][22][23][24][25][26][27][28][29][30][31] and even distinguishing optical isomers or purifying a racemate mixture [32][33][34][35][36][37][38][39][40][41][42][43][44]. The most general models of population transfer were applied.…”

“…The most general models of population transfer were applied. For instance, population inversion via π pulses were used with sequences of IR pulses [19][20][21]32] or a single short IR pulse, acting in a pump-dump mechanism [22][23][24][25]. Despite using relatively simple models, much attention was devoted to analyzing the robustness of the schemes to different types of intra-or inter-molecular couplings [23,45].…”