99 research outputs found
Quantum state tomography of dissociating molecules
Using tomographic reconstruction we determine the complete internuclear
quantum state, represented by the Wigner function, of a dissociating I2
molecule based on femtosecond time resolved position and momentum distributions
of the atomic fragments. The experimental data are recorded by timed ionization
of the photofragments with an intense 20 fs laser pulse. Our reconstruction
method, which relies on Jaynes' maximum entropy principle, will also be
applicable to time resolved position or momentum data obtained with other
experimental techniques
Colloquium: aligning molecules with strong laser pulses
We review the theoretical and experimental status of intense laser alignment\u8212a field at the interface between intense laser physics and chemical dynamics with potential applications ranging from high harmonic generation and nanoscale processing to stereodynamics and control of chemical reactions. After placing the intense laser approach in context with other alignment techniques, we proceed with a discussion of the physics underlying this technique and a description of methods of observing it in the laboratory. The roles played by the laser frequency, the pulse duration, and the system temperature are illustrated numerically and experimentally. Alignment is extended to three-dimensional orientational control, a method of hindering the rotation about all three axes of polyatomic molecules. We conclude with a discussion of potential applications of intense laser alignment.NRC publication: Ye
Laser-induced rotation of iodine molecules in He-nanodroplets: revivals and breaking-free
Rotation of molecules embedded in He nanodroplets is explored by a
combination of fs laser-induced alignment experiments and angulon quasiparticle
theory. We demonstrate that at low fluence of the fs alignment pulse, the
molecule and its solvation shell can be set into coherent collective rotation
lasting long enough to form revivals. With increasing fluence, however, the
revivals disappear -- instead, rotational dynamics as rapid as for an isolated
molecule is observed during the first few picoseconds. Classical calculations
trace this phenomenon to transient decoupling of the molecule from its He
shell. Our results open novel opportunities for studying non-equilibrium
solute-solvent dynamics and quantum thermalization.Comment: 6+7 pages; 4+1 figures; 1 tabl
Making the best of mixed-field orientation of polar molecules: A recipe for achieving adiabatic dynamics in an electrostatic field combined with laser pulses
We have experimentally and theoretically investigated the mixed-field
orientation of rotational-state-selected OCS molecules and we achieve strong
degrees of alignment and orientation. The applied moderately intense nanosecond
laser pulses are long enough to adiabatically align molecules. However, in
combination with a weak dc electric field, the same laser pulses result in
nonadiabatic dynamics in the mixed-field orientation. These observations are
fully explained by calculations employing, both, adiabatic and non-adiabatic
time-dependent models.Comment: 5 pages, 4 figure
Laser-induced 3D alignment and orientation of quantum-state-selected molecules
A strong inhomogeneous static electric field is used to spatially disperse a
rotationally cold supersonic beam of 2,6-difluoroiodobenzene molecules
according to their rotational quantum state. The molecules in the lowest lying
rotational states are selected and used as targets for 3-dimensional alignment
and orientation. The alignment is induced in the adiabatic regime with an
elliptically polarized, intense laser pulse and the orientation is induced by
the combined action of the laser pulse and a weak static electric field. We
show that the degree of 3-dimensional alignment and orientation is strongly
enhanced when rotationally state-selected molecules, rather than molecules in
the original molecular beam, are used as targets.Comment: 8 pages, 7 figures; v2: minor update
Strongly aligned molecules inside helium droplets in the near-adiabatic regime
Iodine (I) molecules embedded in He nanodroplets are aligned by a 160 ps
long laser pulse. The highest degree of alignment, occurring at the peak of the
pulse and quantified by , is measured as a
function of the laser intensity. The results are well described by calculated for a gas of isolated molecules each
with an effective rotational constant of 0.6 times the gas-phase value, and at
a temperature of 0.4 K. Theoretical analysis using the angulon quasiparticle to
describe rotating molecules in superfluid helium rationalizes why the alignment
mechanism is similar to that of isolated molecules with an effective rotational
constant. A major advantage of molecules in He droplets is that their 0.4 K
temperature leads to stronger alignment than what can generally be achieved for
gas phase molecules -- here demonstrated by a direct comparison of the droplet
results to measurements on a 1 K supersonic beam of isolated molecules.
This point is further illustrated for more complex system by measurements on
1,4-diiodobenzene and 1,4-dibromobenzene. For all three molecular species
studied the highest values of achieved in
He droplets exceed 0.96.Comment: 11 pages, 8 figure
Orientation-dependent ionization yields from strong-field ionization of fixed-in-space linear and asymmetric top molecules
The yield of strong-field ionization, by a linearly polarized probe pulse, is
studied experimentally and theoretically, as a function of the relative
orientation between the laser field and the molecule. Experimentally, carbonyl
sulfide, benzonitrile and naphthalene molecules are aligned in one or three
dimensions before being singly ionized by a 30 fs laser pulse centered at 800
nm. Theoretically, we address the behaviour of these three molecules. We
consider the degree of alignment and orientation and model the angular
dependence of the total ionization yield by molecular tunneling theory
accounting for the Stark shift of the energy level of the ionizing orbital. For
naphthalene and benzonitrile the orientational dependence of the ionization
yield agrees well with the calculated results, in particular the observation
that ionization is maximized when the probe laser is polarized along the most
polarizable axis. For OCS the observation of maximum ionization yield when the
probe is perpendicular to the internuclear axis contrasts the theoretical
results.Comment: 14 pages, 4 figure
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