Strongly aligned and oriented molecular samples at a kHz repetition rate

We demonstrate strong adiabatic laser alignment and mixed-field orientation at kHz repetition rates. We observe degrees of alignment as large as cos\Theta=0.94 at 1 kHz operation for iodobenzene. The experimental setup consist of a kHz laser system simultaneously producing pulses of 30 fs (1.3 mJ) and 450 ps (9 mJ). A cold 1 K state-selected molecular beam is produced at the same rate by appropriate operation of an Even-Lavie valve. Quantum state selection has been obtained using an electrostatic deflector. A camera and data acquisition system records and analyzes the images on a single-shot basis. The system is capable of producing, controlling (translation and rotation) and analyzing cold molecular beams at kHz repetition rates and is, therefore, ideally suited for the recording of ultrafast dynamics in so-called "molecular movies".Comment: 6 pages, 4 figures, in press in Mol. Phys., accepted in February 2013, in final production (galley proofs done) since March 8, 2013, v3 only adds publication dat

Improved spatial separation of neutral molecules

We have developed and experimentally demonstrated an improved electrostatic deflector for the spatial separation of molecules according to their dipole-moment-to-mass ratio. The device features a very open structure that allows for significantly stronger electric fields as well as for stronger deflection without molecules crashing into the device itself. We have demonstrated its performance using the prototypical OCS molecule and we discuss opportunities regarding improved quantum-state-selectivity for complex molecules and the deflection of unpolar molecules.Comment: 6 figure

Two-state wave packet for strong field-free molecular orientation

We demonstrate strong laser-field-free orientation of absolute-ground-state carbonyl sulfide molecules. The molecules are oriented by the combination of a 485-ps-long non-resonant laser pulse and a weak static electric field. The edges of the laser pulse create a coherent superposition of two rotational states resulting in revivals of strong transient molecular orientation after the laser pulse. The experimentally attained degree of orientation of 0.6 corresponds to the theoretical maximum for mixing of the two states. Switching off the dc field would provide the same orientation completely field-free

Photophysics of indole upon x-ray absorption

A photofragmentation study of gas-phase indole (C$_8$H$_7$N) upon single-photon ionization at a photon energy of 420 eV is presented. Indole was primarily inner-shell ionized at its nitrogen and carbon $1s$ orbitals. Electrons and ions were measured in coincidence by means of velocity map imaging. The angular relationship between ionic fragments is discussed along with the possibility to use the angle-resolved coincidence detection to perform experiments on molecules that are strongly oriented in their recoil-frame. The coincident measurement of electrons and ions revealed fragmentation-pathway-dependent electron spectra, linking the structural fragmentation dynamics to different electronic excitations. Evidence for photoelectron-impact self-ionization was observed.Comment: 11 pages, 6 figure

Improved spatial separation of neutral molecules

We have developed and experimentally demonstrated an improved electrostatic deflector for the spatial separation of molecules according to their dipole-moment-to-mass ratio. The device features a very open structure that allows for significantly stronger electric fields as well as for stronger deflection without molecules crashing into the device itself. We have demonstrated its performance using the prototypical carbonyl sulfide molecule and we discuss opportunities regarding improved quantum-state-selectivity for complex molecules and the deflection of unpolar molecules

Adiabatic Mixed-Field Orientation of Ground-State-Selected Carbonyl Sulfide Molecules

We experimentally demonstrated strong adiabatic mixed-field orientation of carbonyl sulfide molecules (OCS) in their absolute ground state of $\text{N}_{\text{up}}/\text{N}_{\text{tot}}=0.882$. OCS was oriented in combined non-resonant laser and static electric fields inside a two-plate velocity map imaging spectrometer. The transition from non-adiabatic to adiabatic orientation for the rotational ground state was studied by varying the applied laser and static electric field. Above static electric field strengths of 10 kV/cm and laser intensities of $10^{11} \text{W/cm}^2$ the observed degree of orientation reached a plateau. These results are in good agreement with computational solutions of the time-dependent Schr\'odinger equation

Adiabatic mixed-field orientation of ground-state-selected carbonyl sulfide molecules

We experimentally demonstrated strong adiabatic mixed-field orientation of carbonyl sulfide molecules (OCS) in their absolute ground state of $\text{N}_{\text{up}}/\text{N}_{\text{tot}}=0.882$. OCS was oriented in combined non-resonant laser and static electric fields inside a two-plate velocity map imaging spectrometer. The transition from non-adiabatic to adiabatic orientation for the rotational ground state was studied by varying the applied laser and static electric field. Above static electric field strengths of 10 kV/cm and laser intensities of $10^{11} \text{W/cm}^2$ the observed degree of orientation reached a plateau. These results are in good agreement with computational solutions of the time-dependent Schr\'odinger equation

Controlled molecules to investigate ultrafast chemical dynamics directly in the molecular frame

A molecule’s chemical behavior is governed by its electronic and nuclear properties. Imaging the temporal evolution of the valence electrons and the positions of the atoms during a chemical reaction provides direct insight into fundamental chemical processes. State-selected, strongly aligned and oriented molecular ensembles serve as ideal samples to study ultrafast chemical dynamics in the molecular frame [1]. Such dynamics can be extracted, for instance, via molecular-frame photoelectron angular distributions (MFPADs) [2]. We have developed techniques to manipulate the motion of molecules in cold supersonic beams using strong inhomogeneous electric and laser fields [3]. The state-selected molecules are aligned or oriented by the combined effect of a dc electric field and moderately strong laser pulses with tunable duration between 50 fs and 500 ps. This allows for non-adiabatic as well as adiabatic alignment. We will present our work on the alignment and orientation of carbonyl sulphide (OCS): We have created, for example, coherent superpositions of pendular states in the strong field of the alignment laser that resulted in pendular motion [4] or strong laser-field-free orientation of absolute-ground-state OCS [5]. Subsequently, we have applied the obtained knowledge to the control of complex molecules.Furthermore, MFPADs of indole and indole-water1 clusters were used to topographically build up a 3D MFPAD. These can be discussed using two different theoretical models, i.e., first, an approach based on the strong-field approximation and, second, employing time-dependent density functional theory.References:[1] C. Z. Bisgaard et al. Science, 323, 1464–1468 (2009)[2] L. Holmegaard et al., Nature Physics, 6, 428 (2010).[3] S. Trippel et al., Mol. Phys. 111, 1738 (2013)[4] S. Trippel et al., Phys. Rev. A 89, 051401(R) (2014)[5] S. Trippel et al., Phys. Rev. Lett. 114, 103003 (2015