Subcycle Controlled Charge-Directed Reactivity with Few-Cycle Midinfrared Pulses

Abstract

The steering of electron motion in molecules is accessible with waveform-controlled few-cycle laser light and may control the outcome of light-induced chemical reactions. An optical cycle of light, however, is much shorter than the duration of the fastest dissociation reactions, severely limiting the degree of control that can be achieved. To overcome this limitation, we extended the control metrology to the midinfrared studying the prototypical dissociative ionization of D(2) at 2.1 μm. Pronounced subcycle control of the directional D(+) ion emission from the fragmentation of D(2)(+) is observed, demonstrating unprecedented charge-directed reactivity. Two reaction pathways, showing directional ion emission, could be observed and controlled simultaneously for the first time. Quantum-dynamical calculations elucidate the dissociation channels, their observed phase relation, and the control mechanisms.

Understanding the role of phase in chemical bond breaking with coincidence angular streaking

“…2c) for E k 40.6 eV. This confirms that our measured asymmetry is indeed due to interference between the 1o and net-2o dissociating wavepackets [20][21][22][23][24][25][26][27][28][29][30]32 . In our second two-state quantum mechanical model, we numerically solved the one-dimensional time-dependent Schrödinger equation for the vibrational nuclear wavepacket 33 …”

“…Electron localization in the breakup of hydrogen molecular ions has previously been observed [20][21][22][23][24] with symmetry-broken laser fields produced by CEP stabilizing a few-cycle pulse [20][21][22] or by composing a pulse of two different carrier frequencies 23,24 . The asymmetric fields drive and eventually localize the bound electron at one of the dissociating nuclei 25 .…”

“…A vibrational nuclear wavepacket on the 1ss g þ curve is created by the early part of the laser pulse at time t i . The wavepacket is coupled forth-and-back between the 2ps u þ and 1ss g þ states at later times (t c ) when the energy gap between the potential curves matches the photon energy (or three times the photon energy), with the molecular ion eventually dissociating into H þ þ H. Because of the coherent superposition of 1ss g þ and 2ps u þ contributions [20][21][22][23][24][25][26][27][28][29][30] , the electron probability density localizes asymmetrically at the nuclei. This electron localization dynamics is governed by the laser phase at the instant of field ionization (t i ) and by the coupling times t c,3o , t c,1o and t 0 c,1o , which depend on the chosen photon energy and on the shape of the potential energy curves involved.…”

“…The kinetic energy spectrum shifts when f el mol is changed by 180°. This is indicative of a kinetic-energy-dependent asymmetric dissociation or electron localization due to the interference between the 1o-and net-2o-dissociating wavepackets [20][21][22][23][24][25][26][27][28][29][30]32 .…”

MAKING OPTICAL WAVES, TRACING ELECTRONS IN REAL-TIME: THE ONSET OF THE ATTOSECOND REALM (Invited Review)

“…The cosine wave gives rise to a smooth spectrum in the cutoff range, suggesting emission in a single burst of potentially sub-fs duration, whereas the appearance of modulation for the sine wave suggests that that the emission is distributed in two bursts half a cycle apart. complex molecules [33,34] or towards the sub-cycle manipulation of EUV generation in strongly driven surface plasmas [35] and the photoemission from metal nanotips [36].…”