Thin liquid sheet jet flows in vacuum provide a new platform for performing experiments in the liquid phase, for example X-ray spectroscopy. Micrometer thickness, high stability and optical flatness are the key characteristics required for successful exploitation of these targets. A novel strategy for generating sheet jets in vacuum is presented in this article. Precision nozzles were designed and fabricated using high resolution (0.2 µm) 2-photon 3D printing and generated 1.49±0.04 µm thickness, stable and <λ/20-flat jets in isopropanol under normal atmosphere and under vacuum at 5×10 −1 mbar. The thin sheet technology also holds great promise for advancing the fields of high harmonic generation in liquids, laser acceleration of ions as well as other fields requiring precision and high repetition rate targets.

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Rotational wave packets of the weakly bound C 2 H 2 -He complex have been created using impulsive alignment. The coherent rotational dynamics were monitored for 600 ps enabling extraction of a frequency spectrum showing multiple rotational energy levels up to J ¼ 4. spectrum has been combined with ab initio calculations to show that the complex has a highly delocalized structure and is bound only by ca. 7 cm −1 . The experiments demonstrate how highly featured rotational spectra can be obtained from an extremely cold environment where only the lowest rotational energy states are initially populated. DOI: 10.1103/PhysRevLett.113.043004 PACS numbers: 33.20.-t, 33.80.-b, 36.40.Mr Weakly bound molecular complexes are important model systems for condensed matter held together by van der Waals forces [1]. The weak binding leads to large amplitude motion and delocalized structures that are often reflected in complex rotational spectra that cannot easily be categorized through rigid rotor models. Furthermore, obtaining these spectral features imposes practical problems associated with the very low temperatures that are required to form weakly bound complexes. The low temperatures imply the population of only the lowest quantum states. Consequently, the features in conventional rotational (microwave) spectroscopy comprise only a few lines-often not enough for a comprehensive analysis of the structure of the complex [2].A potential solution to this problem is to use impulsive alignment to generate rotational wave packets through the nonresonant interaction of an intense laser field with a molecule, aligning it in space [3]. Tuning the laser pulse duration and intensity controls the number of rotational eigenstates that contribute to the wave packets. Using this technique for isolated molecules it is possible to monitor the evolution of alignment in time, simultaneously obtaining information on the rotational dynamics and structure [3][4][5][6][7][8][9][10]. The extension of this technique to complex systems where weak interactions are important has been postulated theoretically [11], and demonstrated on the very simplest of systems, noble-gas dimers [12]. The extension of impulsive alignment to van der Waals complexes with internal and delocalized structures remains a challenge. This is due in part to the weak binding and floppy nature of the complex, but also due to the increased complexity of the resulting rotational spectrum, such that currently, to the best of our knowledge, no such measurement has been reported.This approach may also have potential for exploring liquids, where the wave-packet dynamics will be sensitive to dephasing. A particularly promising liquid to begin such studies is superfluid helium. Frequency-domain spectra of molecules embedded into large superfluid helium droplets show sharp rotational transitions, suggesting that wave packets will not dephase [2,13]. However, the recent attempt to impulsively align molecules in large helium droplets by Pentlehner et al. suggests that this may not be th...

We show that rotational line spectra of molecular clusters with near zero permanent dipole moments can be observed using impulsive alignment. Aligned rotational wavepackets were generated by non-resonant interaction with intense femtosecond laser pump pulses and then probed using Coulomb explosion by a second, time-delayed femtosecond laser pulse. By means of a Fourier transform a rich spectrum of rotational eigenstates was derived. For the smallest cluster, C 2 H 2 -He, we were able to establish essentially all rotational eigenstates up to the dissociation threshold on the basis of theoretical level predictions. The C 2 H 2 -He complex is found to exhibit distinct features of large amplitude motion and very early onset of free internal rotor energy level structure.

Nanoparticles produced when ethanol jet exits nozzle (a), over silver vapour source (b), captured in a cold trap (c).