Laser control activation

The invention of schemes to induce and observe dynamical processes in molecules employing ultrashort laser pulses has founded research areas with the names Femtochemistry and Femtobiology [1-8], culminating with the Nobel Prize awarded to Ahmed Zewail for his achievements in femtosecond spectroscopy [9,10]. More recently, the technology of pulse shaping [11,12] has opened up the field of laser control of chemical reactions, until then populated only by theorists [13-17]. This has been an active area of research in recent years [18— 23], and textbooks [24-26] as well as many reviews [27-40] have been published on the topic. 

One of the advantages of lasers for activating gas phase reactions is the feasibility to control the dimension of the process zone by laser focus. In this way very small regions may be achieved where nucleation and particle growth happen. The same advantage is applicable to processes where the laser is used for evaporating coarse ceramic material in order to get nano-scale ceramic powders by re-condensation via homogeneous nucleation [232]. This technique has also been used to prepare SiC nanopowder with yields up to 100 g h [233]. However, with this approach, traces of free silicon were also detectable. 

P. Heinz, M. Fickenscher, A. Lauberau, Electro-optic gain control and cavity dumping of a Nd glass laser with active passive mode-locking. Opt. Commun. 62,343 (1987)... 

Wave packet propagation phenomena influenced by electronic perturbations and by intramolecular vibrational redistributions (IVR) these phenomena are studied for extremely cold alkali dimers (K2, Na2) and trimers (K3, Naa). A highlight is the possibility to control actively the molecular dynamics of these species under certain experimental conditions, by means of ultrashort laser pulses. 

Replacement gas is provided using two gas cylinders and a fluorine generator. Figure 5.7 shows the mechanical system for refilling the lasers. One gas cylinder provides the helium and the other provides the premix of other gases. The fluorine source is initially in the solid form of potassium fluoride. During filling, the laser s controller activates heaters that raise the temperature of the solid compound, which... 

Several heterostructure geometries have been developed since the 1970s to optimize laser performance. Initial homojunction lasers were advanced by the use of heterostmctures, specifically the double-heterostmcture device where two materials are used. The abiUty of the materials growth technology to precisely control layer thickness and uniformity has resulted in the development of multiquantum well lasers in which the active layer of the laser consists of one or mote thin layers to allow for improved electron and hole confinement as well as optical field confinement. 

Osmotic Control. Several oral osmotic systems (OROS) have been developed by the Alza Corporation to allow controUed deHvery of highly water-soluble dmgs. The elementary osmotic pump (94) consists of an osmotic core containing dmg surrounded by a semi-permeable membrane having a laser-drilled deHvery orifice. The system looks like a conventional tablet, yet the outer layer allows only the diffusion of water into the core of the unit. The rate of water diffusion into the system is controUed by the membrane s permeabUity to water and by the osmotic activity of the core. Because the membrane does not expand as water is absorbed, the dmg solution must leave the interior of the tablet through the smaU orifice at the same rate that water enters by osmosis. The osmotic driving force is constant until aU of the dmg is dissolved thus, the osmotic system maintains a constant deHvery rate of dmg until the time of complete dissolution of the dmg. 

Linearly polarized, near-diffraction-hmited, mode-locked 1319 and 1064 nm pulse trains are generated in separate dual-head, diode-pumped resonators. Each 2-rod resonator incorporates fiber-coupled diode lasers to end-pump the rods, and features intracavity birefringence compensation. The pulses are stabilized to a 1 GHz bandwidth. Timing jitter is actively controlled to < 150 ps. Models indicate that for the mode-locked pulses, relative timing jitter of 200 ps between the lasers causes <5% reduction in SFG conversion efficiency. 

During the course of the last century, it was realized that many properties of solids are controlled not so much by the chemical composition or the chemical bonds linking the constituent atoms in the crystal but by faults or defects in the structure. Over the course of time the subject has, if anything, increased in importance. Indeed, there is no aspect of the physics and chemistry of solids that is not decisively influenced by the defects that occur in the material under consideration. The whole of the modem silicon-based computer industry is founded upon the introduction of precise amounts of specific impurities into extremely pure crystals. Solid-state lasers function because of the activity of impurity atoms. Battery science, solid oxide fuel cells, hydrogen storage, displays, all rest upon an understanding of defects in the solid matrix. 

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