Clusters of 2x10(3) to 4x10(4) Ar atoms are Coulomb exploded in intense (up to 8x10(15) W cm(-2)) laser fields. The dependence of multiply charged argon ion energies on the polarization state of light is probed. A directional asymmetry in the ion-explosion energies is observed for the highest charge states. The ion-energy distribution consists of a low-energy isotropic component, and a high-energy anisotropic one. The results are discussed in terms of an asymmetric Coulomb-explosion scenario.

We demonstrate that strong laser pulses can induce torsional motion in a molecule consisting of a pair of phenyl rings. A nanosecond laser pulse spatially aligns the carbon-carbon bond axis, connecting the two phenyl rings, allowing a perpendicularly polarized, intense femtosecond pulse to initiate torsional motion accompanied by an overall rotation about the fixed axis. We monitor the induced motion by femtosecond time-resolved Coulomb explosion imaging. Our theoretical analysis accounts for and generalizes the experimental findings.

It is demonstrated that strong laser pulses can introduce torsional motion in the axially chiral molecule 3,5-difluoro-3('),5(')-dibromobiphenyl. A nanosecond laser pulse spatially aligns the stereogenic carbon-carbon (C-C) bond axis allowing a perpendicularly polarized, intense femtosecond pulse to initiate torsional motion accompanied by a rotation about the fixed axis. We monitor the induced motion by femtosecond time-resolved Coulomb explosion imaging. Our theoretical analysis corroborates the experimental findings and on the basis of these results we discuss future applications of laser-induced torsion, viz., time-resolved studies of deracemization and laser controlled molecular junctions based on molecules with torsion.

One-dimensional alignment of molecules in the adiabatic limit, where the pulse duration greatly exceeds the molecular rotational periods, is studied experimentally. Four different asymmetric top molecules (iodobenzene, p-diiodobenzene, 3,4-dibromothiophene, and 4,4'-dibromobiphenyl), rotationally cooled through a high pressure supersonic pulsed valve, are aligned by a 9-ns-long pulse. Their orientations are measured through Coulomb explosion, induced by a 130-fs-long pulse, and by recording the direction of the recoiling ions. The paper focuses on the crucial role of the initial rotational temperature for the degree of alignment. In particular, we show that at molecular temperatures in the 1 K range very strong alignment is obtained already at intensities of a few times 10(11) W/cm2 for all four molecules. At the highest intensities (approximately 10(12) W/cm2) the molecules can tolerate without ionizing >or=0.92 in the case of iodobenzene. This is the strongest degree of alignment ever reported for any molecule.

Energetic, highly-charged oxygen ions, O q+ (q ≤ 6), are copiously produced upon laser field-induced disassembly of highly-charged water clusters, (H 2 O) n and (D 2 O) n , n ∼ 60, that are formed by seeding high-pressure helium or argon with water vapor. Ar n clusters (n∼40000) formed under similar experimental conditions are found undergo disassembly in the Coulomb explosion regime, with the energies of Ar q+ ions showing a q 2 dependence. Water clusters, which are argued to be considerably smaller in size, should also disassemble in the same regime, but the energies of fragment O q+ ions are found to depend linearly on q which, according to prevailing wisdom, ought to be a signature of hydrodynamic expansion that is expected of much larger clusters. The implication of these observations on our understanding of the two cluster explosion regimes, Coulomb explosion and hydrodynamic expansion, is discussed. Our results indicate that charge state dependences of ion energy do not constitute an unambiguous experimental signature of cluster explosion regime.