arXiv subjects

D. Mathur

Publications and source records attributed to D. Mathur.

25 records · Page 2Linked to original sources

arXiv2003

Explosions of water clusters in intense laser fields

Energetic, highly-charged oxygen ions, $O^{q+}$ ($q\leq 6$), are copiously produced upon laser field-induced disassembly of highly-charged water clusters, $(H_2O)_n$ and $(D_2O)_n$, $n\sim$ 60, that are formed by seeding high-pressure helium or argon with water vapor. $Ar_n$ clusters (n$\sim$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.

physics.atm-clus↗

arXiv2003

Anisotropic "charge-flipping" acceleration of highly charged ions from $(N_2)_n$ clusters in strong optical fields

The disassembly of molecular clusters $(N_2)_n$ ($n$=50-3000) in strong optical fields is investigated using two-dimensional time-of-flight spectrometry. Very highly charged ions are formed with a two-component energy distribution. A low-energy, isotropic component correlates with Coulomb explosion. A high-energy, anisotropic component, that results from a ``charge flipping" acceleration mechanism, gives rise to ions with energies in excess of the Coulombic limit.

physics.atm-clus↗

arXiv2002

Asymmetric emission of high energy electrons in the two-dimensional hydrodynamic expansion of large xenon clusters irradiated by intense laser fields

Energy spectra and angular distributions have been measured of electrons that are emitted upon disassembly of $Xe_{150000}$ following irradiation by intense (10$^{15}-10^{16}$ W cm$^{-2}$) laser pulses whose durations are varied over the 100-2200 fs range. The cluster explosion dynamics occur in the hydrodynamic regime. Electron emission is found to be unexpectedly asymmetric and exhibits a resonance when the laser pulse duration is $\sim$1 ps. These results are rationalized by extending the hydrodynamic model to also take into account the force that the light field exerts on the polarization charge that is induced on surface of the cluster. We show that the magnitude of this electrostrictive force is comparable to those of Coulombic and the hydrodynamic forces, and it exhibits resonance behavior. Contrary to earlier understanding, we find that low-energy electrons are connected to the resonance in energy absorption by the cluster. The high-energy electrons seem to be produced by a mechanism that is not so strongly influenced by the resonance.

physics.atm-clus↗

arXiv2000

Irradiation of benzene molecules by ion-induced and light-induced intense fields

Benzene, with its sea of delocalized $π$-electrons in the valence orbitals, is identified as an example of a class of molecules that enable establishment of the correspondence between intense ion-induced and laser-light-induced fields in experiments that probe ionization dynamics in temporal regimes spanning the attosecond and picosecond ranges.

physics.atom-ph↗

arXiv2000

The propensity of molecules to spatially align in intense light fields

The propensity of molecules to spatially align along the polarization vector of intense, pulsed light fields is related to readily-accessible parameters (molecular polarizabilities, moment of inertia, peak intensity of the light and its pulse duration). Predictions can now be made of which molecules can be spatially aligned, and under what circumstances, upon irradiation by intense light. Accounting for both enhanced ionization and hyperpolarizability, it is shown that {\it all} molecules can be aligned, even those with the smallest static polarizability, when subjected to the shortest available laser pulses (of sufficient intensity).

physics.atom-ph↗

arXiv1999

Dynamic and geometric alignment of CS_2 in intense laser fields of picosecond and femtosecond duration

CS$_2$ is identified as a molecule for which distinction can be made between dynamic and geometric alignment induced by intense laser fields. Measured anisotropic angular distributions of fragment ions arise from (i) dynamic alignment of the S-C-S axes along the laser polarization vector for 35-ps laser pulses and (ii) geometric alignment due to an angle-dependent ionization rate in the case of 100-fs pulses. Results of classical calculations of the alignment dynamics support our observations. By comparing mass spectra obtained with linearly- and circularly-polarized light it is not possible to distinguish between dynamic and geometric alignment. 33.80.Rv, 33.90.+h, 42.50.Vk

physics.atom-ph↗

arXiv1998

Electron attachment to valence-excited CO

The possibility of electron attachment to the valence $^{3}Π$ state of CO is examined using an {\it ab initio} bound-state multireference configuration interaction approach. The resulting resonance has $^{4}Σ^{-}$ symmetry; the higher vibrational levels of this resonance state coincide with, or are nearly coincident with, levels of the parent $a^{3}Π$ state. Collisional relaxation to the lowest vibrational levels in hot plasma situations might yield the possibility of a long-lived CO$^-$ state.

physics.atom-ph↗