Laser Wave Drives Electrons

At Max-Planck-Institut, Dr. Matthias Kling and his collaborators studied the influence of intense linearly-polarized laser pulses with duration of 5 femtoseconds on the motion of electrons in a chemical bond. In the experiments, positively-charged deuterium molecules (D2+), also known as heavy hydrogen, were used. These molecules are very simple: they consist of two positively charged ions (the D+ nuclei, each containing a proton and a neutron), and one electron that is left behind following ionization of neutral D2 with a laser pulse.

With a special camera the scientists measured the emission direction of deuterium ions (D+) and deuterium atoms (D) after dissociation of D2+ molecules with respect to the laser polarization axis.
As long as the scientists used conventional laser pulses without phase control, equal numbers of deuterium ions (as well as atoms) were ejected in both directions along the laser polarization axis.

Figure of dissociation of a deuterium molecule
Dissociation of a deuterium molecule: it falls apart into a D+ ion and a neutral D-atom; © AMOLF/MPQ

Using phase-controlled pulses with a specific value of the phase, deuterium ions and deuterium atoms were preferentially emitted to the right and left, respectively. A simple shift of the phase to 180 degrees, resulting in the same waveform with the oscillations flipped around the propagation axis, turns the outcome of this simple laser-induced reaction into the opposite: the D+ ions preferable fly to the left and the D atoms to the right. On the basis of quantum mechanical calculations the scientists can explain the observed phenomenon. These results are published in the journal Science.

Processes, in which electrons are transported, are extremely important in chemistry and biology. For example, electron transfer plays an important role in both damage and repair of DNA. The here described results of the Dutch-German research team on the dissociation of hydrogen molecules may provide a clue how to control the transfer of electrons in larger systems using the electric field of light. This work may also have an impact on the new field of molecular electronics, where the flow of electrons between molecules may be steered in a controlled way with laser pulses.; Source: Max-Planck-Institut für Quantenoptik