Intense 2-cycle laser pulses induce time-dependent bond-hardening in a polyatomic molecule

A time-dependent bond-hardening process is discovered in a polyatomic molecule (tetramethyl silane, TMS) using few-cycle pulses of intense 800 nm light. In conventional mass spectrometry, symmetrical molecules like TMS do not exhibit a prominent molecular ion (TMS$^+$) as unimolecular dissociation into [Si(CH$_3$)$_3]^+$ proceeds very fast. Under strong field and few-cycle conditions, this dissociation channel is defeated by time-dependent bond-hardening: a field-induced potential well is created in the TMS$^+$ potential energy curve that effectively traps a wavepacket. The time-dependence of this bond hardening process is verified using longer-duration ($\geq$ 100 fs) pulses; the relatively "slower" fall-off of optical field in such pulses allows the initially trapped wavepacket to leak out, thereby rendering TMS$^+$ unstable once again. Our results are significant as they demonstrate (i) optical generation of polyatomic ions that are normally inaccessible and (ii) optical control of dynamics in strong fields, with distinct advantages over weak-field control scenarios that demand a narrow bandwidth appropriate for a specified transition.Comment: To appear in Phys. Rev. Let

Study of the photovoltaic effect in thin film barium titanate

The photoelectric effect in structures consisting of metal deposited barium titanate film silicon is described. A radio frequency sputtering technique is used to deposit ferroelectric barium titantate films on silicon and quartz. Film properties are measured and correlated with the photoelectric effect characteristics of the films. It was found that to obtain good quality pin hole free films, it is necessary to reduce the substrate temperature during the last part of the deposition. The switching ability of the device with internal applied voltage is improved when applied with a ferroelectric memory device

Decision-Stage Method: Convergence Proof, Special Application, and Computation Experience

This paper presents a new method for obtaining exact optimal solutions for a class of discrete-variable non-linear resource-allocation problems. The new method is called the decision-state method because, unlike the conventional dynamic programming method which works only in the state space, the new method works in the state space and the decision space. It generates and retains only a fraction of the points in the state space at which the state functions are discontinuous; and thus overcomes to some extent the curse of dimensionality. It carries the cumulative decision-strongs associated with these points, and thus avoids the backtracking entailed by the conventional dynamic programming method for recovering the optimal decisions. A concise and complete statement of the method is given in Algorithm 2 and it is proved that the algorithm finds all exact optimal solutions. In addition the method is adapted for solving some problems with special structures such as block-angular or split-block-angular constraints and the resultant substantial advantages are demonstrated. The performance of Algorithm 2 on many resource-allocations problems is reported, along with investigations on many tactical decisions which have substantial impact on the performance. The performance of the computer implementation of Algorithm 2 is compared with that of the MMDP algorithm and it showed that for the class of problems at which the two are aimed, the decision-state Algorithm 2 performed better than MMDP algorithm both in terms of storage requirement and solution time. In fact, it achieved an order of magnitude saving in storage requirement.

Control of the Onset of Filamentation in Condensed Media

Propagation of intense, ultrashort laser pulses through condensed media like crystals of BaF$_2$ and sapphire results in the formation of filaments. We demonstrate that the onset of filamentation may be controlled by rotating the plane of polarization of incident light. We directly visualize filamentation in BaF_2 via six-photon absorption-induced fluorescence and, concomitantly, by probing the spectral and spatial properties of white light that is generated.Comment: To appear in Phys. Rev.

Molecular Dynamics Simulation of Carbon Nanotube & Pulmonary Surfactant Protein - B Interactions

Absorption of proteins onto carbon nanotubes is important part of biomedical engineering because it is helpful to fabricate stable, compatible and sensitive scaffold, which is the basic step of fabricating biosensors. Many previous researches show that most of the proteins can be absorbed on surface of carbon nanotube. However, the mechanism of this absorption is not specific clear. In this lecture, mechanism of protein absorbed on nanotube will be explained by molecular dynamics(MD) using NAMD and VMD software package