Olga Smirnova receives the Karl Scheel Prize 2010

5th. February 2010

Dr. Olga Smirnova, head of MBI's Juniorgroup in Theory on "Attosecond multielectron dynamics in molecules", receives the Kar Scheel Preis of the year 2010. The prestigeous prize of the Physikalische Gesellschaft zu Berlin (PGzB) is awarded for outstanding scientific work typically achieved after PhD. It includes a cash award of 5.000 €. More about the prize ...

Molecules in real-time – how hydrogen bonds determine structure and function.

5th January 2010

The European Research Council (ERC) has awarded Prof. Thomas Elsaesser an 'Advanced Grant' of 2.49 Million Euros. The project aims at elucidating extremely fast processes which determine the properties of hydrogen bonds in molecular systems.
Thomas Elsaesser who is with the Max-Born-Institute for Nonlinear Optics and Short Pulse Spectroscopy in Berlin, Germany, is one of the leading researchers in ultrafast science, studying ultrafast processes in condensed matter. His project is devoted to unraveling changes of molecular structures on the length scale of a chemical bond and the ultrashort time scale of molecular motions. This work will cover aspects of physics, chemistry and biology. ERC Advanced Grants allow exceptional established research leaders to pursue frontier research of their choice.

Hydrogen bonds are weak chemical bonds and represent a fundamental interaction in Nature. They determine the structure of biomolecules such as deoxyribonucleic acid (DNA), the basic carrier of genetic information in cells. On the other hand, they undergo fluctuations due to their weak binding forces. In water, this leads to extremely fast changes in the arrangement of molecules including the breaking and reformation of hydrogen bonds. Although hydrogen bonds have been studied for a long time, their structural dynamics which occur in the femtosecond time domain (1 femtosecond = 10^-15 s = one millionth of a billionth of a second), are understood only in part.
Within the project, novel methods of ultrafast optics in a wavelength range from the far-infrared to hard x-rays will be applied for investigating hydrogen bonds. A key goal consists in measuring molecular structures in real-time by initiating and reading out structure changes with ultrashort light pulses. X-ray pulses of a wavelength comparable to the length of a chemical bond allow for generating a sequence of 'snapshots' of molecular structure. Infrared pulses give insight into local motions of specific molecular groups. In the experiments, the interaction of DNA with its aqueous environment will be studied, i.e., the coupling of water molecules to different functional units of the DNA double helix, the fluctuations of the water shell around DNA, and the role of water for the redistribution and the transport of energy from DNA into the environment. Hydrogen bonds play a key role for a broad range of biochemical processes and, thus, the results are expected to be of broad relevance. In a second part of the project, structures generated by charge and/or proton transfer will be studied in hydrogen bonded molecular crystals. Such elementary chemical processes govern the electrical properties of the materials which are of interest for applications in novel ferroelectric devices.

Biographical information on Thomas Elsaesser is available at http://staff.mbi-berlin.de/elsasser/

Light pressure – the route to efficient laser ion acceleration

9th December 2009

One of the recent challenges in light-matter interaction consists in the unidirectional acceleration of charged particles by laser light. This can occur through a variety of laser-induced plasma phenomena or, more directly, through transfer of the unidirectional momentum of a propagating laser field, the so-called light pressure.
Utilization of the light pressure requires rather ambitious parameters of laser intensity and temporal pulse shape. In return, theory predicts rather favorable energy conversion efficiencies and narrow ion energy distributions which both are a prerequisites for many applications.
Scientists from the Max Born Institute (MBI) Berlin and from the Max Planck Institute for Quantum Optics (MPQ) Garching and LMU Munich were able to demonstrate this principle in recent experiments (Phys. Rev. Lett. 103 (24), 245003(2009)). The key in the process is to favor the momentum exchange between the laser photons and the target while suppressing unwanted electron heating. Two technologies are essential for this purpose: Ultra-high temporal contrast laser pulses (delivered by the High-Field-Laser at MBI-Berlin) on the one hand and ultimate thin diamond like carbon foils (produced at MPQ/LMU) on the other. The results demonstrate efficient ion beam generation while simultaneously reducing the kinetic energy spread of the ions.
See also Informationsdienst Wissenschaft in english and at Informationsdienst Wissenschaft in german

Carbonic acid now measured in liquid water

Carbonic acid, the hydrated form of carbon dioxide, is one of the most abundant molecules on Earth. Carbonic acid (H₂CO₃), has until now only been detected as isolated molecule in the gas phase and frozen in ice matrices. Adamczyk et al. now describe in a publication in Science Express (12 November 2009) how carbonic acid can be generated using photoacids and detected with transient infrared spectroscopy.
More information: see press releases (in English, German, French and Dutch), highlight and detailed project pages.

Acceleration of neutral atoms in strong short-pulse laser fields

The force experienced by a charged particle in an oscillating electric field is proportional to the cycle-averaged intensity gradient. Extremely strong kinematic forces are now observed on neutral atoms in short-pulse laser fields; the ponderomotive force on electrons is identified as the driving mechanism, leading to probably the highest observed acceleration on neutral atoms in an external field to date.
Scientists of the Max-Born-Institute reported about in the current issue of Nature. These results are featured in the cover story of Nature doi:10.1038/nature08445.
see also
press release Forschungsverbund
Making the paper, Nature 461, 1171 (2009)
Nature Cover
See also articles in:
Physics Update, Physics World, ProPhysik, scinexx, spektrumdirekt, chemie.de

Miniature particle accelerator: Micro-water droplets as a source for laser driven ion acceleration

The cover of Physical Review Letters (Vol. 103 Issue 13) shows a result of a recent MBI publication. In the underlying work (T.Sokollik et al., PRL 103, 135003 (2009)) ion acceleration from isolated spherical targets was investigated by proton imaging for the first time. Already in a previous work (S. Ter Avetisyan et al. PRL 2006), scientists from the Max-Born-Institute in Berlin found that laser irradiated water (or heavy water) droplets can generate a quasi-monoenergetic proton (or deuteron) beam. On the base of simulations they could argue that this, besides additional premises might be connected to a spatially asymmetric field structure which favours a directional emission. Using proton imaging now, the evidence for an advantageous field structure was found which leads to a directional ion beam emission using a micro-sphere target which is a versatile target system. The great advantage of such a system is the MHz repetition rate of droplet generation with a liquid jet. On the other hand, the use of evaporating liquids seems to have a drawback. In case of such targets which evaporate in vacuum, the presence of an ambient plasma counteracts the energy transfer between laser and ion beam. Current investigations aim to avoid these disadvantages of liquids and to explore further fundamental processes of isolated targets.

High harmonic interferometry of multi-electron dynamics in molecules

High harmonic emission occurs when an electron, liberated from a molecule by an incident intense laser field, gains energy from the field and recombines with the parent molecular ion. The emission provides a snapshot of the structure and dynamics of the recombining system, encoded in the amplitudes, phases and polarization of the harmonic light. Here we show with CO2 molecules that high harmonic interferometry can retrieve this structural and dynamic information: by measuring the phases and amplitudes of the harmonic emission, we reveal 'fingerprints' of multiple molecular orbitals participating in the process and decode the underlying attosecond multi-electron dynamics, including the dynamics of electron rearrangement upon ionization. These findings establish high harmonic interferometry as an effective approach to resolving multi-electron dynamics with sub-Ångström spatial resolution arising from the de Broglie wavelength of the recombining electron, and attosecond temporal resolution arising from the timescale of the recombination event.
The scientists Dr. Olga Smirnova of Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie and from National Research Council of Canada published their results at the current issue of Nature (22 July 2009) doi:10.1038/nature08253.

Multispot writing in fused glass

Nature photonics selected recent work from the ongoing collabortion between MBI and Université Jean Monnet at Saint Etienne, France, as one of their Research Highlights. We quote: "Multispot writing in fused glass, Opt. Express 17, 3531–3542 (2009). Owing to its highly deterministic and nonlinear absorption process, infrared femtosecond laser writing offers the means to create buried, localized structural modifications in transparent materials. By moving the sample with respect to the laser's focal point, three-dimensional structures can be inscribed. However, the fabrication of complex structures often involves long processing times. Cyril Mauclair and co-workers from France and Germany have now demonstrated that the problem of speed can be solved by parallel photoinscription that uses multiple laser spots with reconfigurable patterns. The trick is to use a periodical binary phase mask to spatially modulate the wavefront of the laser beam. By varying the period (cycling frequency) of the binary phase, the team show that a simple grating phase mask and therefore dynamic double-spot operation can be achieved. The team use a liquid-crystal spatial light modulator, addressed optically, to create the binary phase mask. A 800-nm Ti:sapphire laser emitting 150-fs pulses at a repetition rate of 10 kHz and with a power of 30 mW is used for the process. By controlling the motion of the sample, the team succeeded in manufacturing three-dimensional light dividers and fabricating wavelength-division demultiplexing devices in fused silica. They are confident that with sufficient energy, more machining foci can be used."

Hot Electrons in Carbon – Graphite behaves like a semiconductor

Markus Breusing, Claus Ropers und Thomas Elsaesser, three scientists from the Max-Born-Institute in Berlin, have now investigated the behavior of electrons in thin graphite films in real time. As they now report in Physical Review Letters (Volume 102, 086809/1-4 (2009)), they recorded the dynamics of electrons with an unprecedented temporal resolution of only 10 femtoseconds (one femtosecond is a millionth of a billionth of a second). Electrons were excited to high energy states with ultrashort laser pulses, and their return to equilibrium was observed. The individual steps of this process are temporally resolved, and the momentary distribution of electrons in the material is identified. Within 30 femtoseconds, electrons form a hot gas with temperatures of 2500 °C, which cools down to about 200 °C in only 500 femtoseconds. The energy dissipated in this process is transferred to the crystal lattice. After this process, the electrons slowly return to their initial states. For the first time, the study shows conclusively that, on ultrashort time scales, graphite behaves like a semiconductor, such as silicon or gallium arsenide, and not like a metal.
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Ionisation dynamics in the light of elliptically polarised femtosecond laser pulses

Scientists from the MBI (I.V. Hertel, I. Shchatsinin, T. Laarmann, N. Zhavoronkov, H.-H. Ritze, and C. P. Schulz) have shown, that elliptically polarized, ultrashort light pulses allow a particularly clear view into the dynamics of ionisation processes in intense laser fields. They found e.g. convincing evidence for a so called „doorway state“ in the football molecule C60 (Buckminsterfullerene), which is populated in a first step prior to ejecting an electron from the molecule. Subsequently the molecule is so strongly deformed, that many other electrons can participate in the process and several of them can finally leave the system – on a time scale of a few femtoseconds. The work, recently published in the renowned Journal Physical Review Letters (Phys. Rev. Lett. 102, 023003 (2009)) has also been included in the Virtual Journals on "Ultrafast Science" and "Nanoscale Science & Technology".