Synthesis of LaB6 micro/nano structures using picosecond (Nd:YAG) laser and its field emission investigations

Micro/nano structures have been obtained by laser surface treatment on sintered LaB₆ pellets employing a picosecond pulsed Nd:YAG laser at a pressure of ∼1×10⁻³ mbar. The X-ray diffraction pattern of the laser treated pellet shows a set of well defined diffraction peaks, indexed to the cubic phase of LaB₆ only. The scanning electron microscope studies reveal formation of micro and nano structures upon laser treatment and the resultant surface morphology is found to be strongly influenced by the laser fluence. Field electron emission studies made on the LaB₆ pellet, treated with optimized laser fluence, have been performed in a planar diode configuration under ultra high vacuum conditions. The threshold field required to draw an emission current density of ∼10 μA/cm² has been found to be ∼2.3 V/μm and a current density of ∼530 μA/cm² has been drawn at an applied field of 5.2 V/μm. The Fowler-Nordheim plot is found to be linear in accordance with the quantum mechanical tunneling phenomenon, confirming the metallic nature of the emitter. The emission current at the pre-set value ∼10 μA shows very good stability over a period of more than 3 hours. The present results emphasize the effectiveness of a picosecond laser treatment towards fabrication of a nano metric LaB₆ emitter for high current density applications.     

Expanding the linear dynamic range for quantitative liquid chromatography-high resolution mass spectrometry utilizing natural isotopologue signals

The linear dynamic range (LDR) for quantitative liquid chromatography–mass spectrometry can be extended until ionization saturation is reached by using a number of target isotopologue ions in addition to the normally used target ion that provides the highest sensitivity. Less abundant isotopologue ions extend the LDR: the lower ion abundance decreases the probability of ion detector saturation. Effectively the sensitivity decreases and the upper limit of the LDR increases. We show in this paper that the technique is particularly powerful with a high resolution time of flight mass spectrometer because the data for all ions are automatically acquired, and we demonstrated this for four small organic molecules; the upper limits of LDRs increased by 25–50 times.     

The effect of dye photodegradation on the performance of dye lasers

Detailed experimental study of laser dye stability and the subsequent effects of photodegradation products on the operation of a Nd:YAG laser pumped Rhodamine-6G pulsed dye oscillator has been carried out. Deterioration of laser output on account of dye photodegradation resulting in the loss of active dye molecules and the generation and accumulation of reaction products that introduce a loss at the laser and pump wavelengths has been theoretically simulated in terms of a time dependent rate equation model. Our experimental observations have been found to be in good agreement with our theoretical estimates. We have also investigated the deterioration in the performance of a copper vapour laser pumped tunable dye laser with a high average power and a high repetition rate operating over an extended period of time. Our theoretical model, when suitably modified, provided useful estimates for the extent of deterioration in laser performance of such a dye laser with a high average power and a high repetition rate on account of photodegradation of the active dye molecules. PACS 42.55.Mv; 42.60.By; 42.70.Hj     

On implementation via demand commitment games

A simple version of the Demand Commitment Game is shown to implement the Shapley value as the unique subgame perfect equilibrium outcome for any n-person characteristic function game. This improves upon previous models devoted to this implementation problem in terms of one or more of the following: a) the range of characteristic function games addressed, b) the simplicity of the underlying noncooperative game (it is a finite horizon game where individuals make demands and form coalitions rather than make comprehensive allocation proposals and c) the general acceptability of the noncooperative equilibrium concept. A complete characterization of an equilibrium strategy generating the Shapley value outcomes is provided. Furthermore, for 3 player games, it is shown that the Demand Commitment Game can implement the core for games which need not be convex but have cores with nonempty interiors. Received March 1995/Final version February 1997     

A study of the plasticity in the vortex matter across the second magnetization peak in a YBCO crystal via measurements of minor hysteresis loops

Results of an investigation of the path dependence of the critical current density J _c due to the plastic deformation of the flux line lattice in a weakly pinned YBa₂Cu₃O_7-δ (YBCO) crystal for H‖c are reported. The procedure of minor hysteresis loops has been used to explore the path dependence of J _c and the metastability effects. Contrary to the behavior observed in low T _c systems. in YBCO it is found that at low temperatures, the multivaluedness in J _c(H) could persist beyond the notional peak field H _p, at which the anomalous variation in J _c(H) reaches its maximum value.     

Quantum interferences from cross talk in J = 1/2 ↔ J = 1/2 transitions

We consider the possibility of a control field opening up multiple pathways and thereby leading to new interference and coherence effects. We illustrate the idea by considering the J = 1/2 ↔ J = 1/2 transition. As a result of the additional pathways, we show the possibilities of nonzero refractive index without absorption and gain without inversion. We explain these results in terms of the coherence produced by the opening of an extra pathway.