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A molecular conveyor belt by controlled delivery of single molecules into ultrashort laser pulses


Trapping and laser cooling in atomic physics enables control of single particles and their dynamics at the quantum level in a background-free environment. Ultrashort intense laser pulses reveal the ultimate control of electromagnetic fields, enabling the imaging of matter, in principle down to a single molecule or virus resolved on atomic scales. However, current methods fall short in overlapping each target with a pulse of comparable size. We combine the two fields by demonstrating a deterministic molecular conveyor, formed of electric trapping potentials. We deliver individual diatomic ions at millikelvin temperatures and with submicrometre positioning into few-femtosecond ultraviolet laser pulses. We initiate and probe the molecule’s femtosecond dynamics and detect it and its response with 100% efficiency. This experiment might become key for investigations of individual molecules, such as structural determinations using few-femtosecond X-ray lasers. Our scheme may overlap each single molecule with a pulse, focused to (sub)micrometre size, providing the required number of photons at the repetition rate of the laser.

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Figure 1: Schematic of the set-up combining the fields of single-particle preparation on the quantum level and single, ultrashort laser pulses.
Figure 2: Preparation of a single molecular ion as a cold, micropositioned target.
Figure 3: Schematic representation of our experiment on a deterministically positioned single molecule, based on the ab initio potential-energy curves of the electronic states involved.
Figure 4: Vibrational motion of molecules derived from the dissociation of single molecules as a function of pump–probe delay for 4 fs laser pulses.

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Financial support is gratefully acknowledged by the Deutsche Forschungsgemeinschaft (DFG), the DFG Cluster of Excellence: Munich Centre for Advanced Photonics, the International Max Planck Research School on Advanced Photon Science and the EU research project PICC: the Physics of Ion Coulomb Crystals, funded under the European Communities Seventh Framework Programme. The authors would like to thank J. Britton, W. Schmid, C. Hackenberger, J. Bayerl, M. Schulze, T. Dou and C. Kerzl for their contributions and H. J. Neusser for support of a continuous-wave cooling laser. We also thank D. Habs for the triggering discussion and G. Rempe for his intellectual and financial support.

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S.K. and G.L. contributed equally to this work. M.K., W.F. and R.d.V-R. developed the theory. A.S., E.B., R.E., F.K., R.K. and T.S. contributed to the experimental work.

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Correspondence to Tobias Schaetz.

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Kahra, S., Leschhorn, G., Kowalewski, M. et al. A molecular conveyor belt by controlled delivery of single molecules into ultrashort laser pulses. Nature Phys 8, 238–242 (2012).

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