A review is presented of the issues associated with the generation of large-volume, high-pressure, nonequilibrium plasmas, as well as the approaches that have been developed for generating these plasmas using electrical discharges in gases. The various instabilities that have been overcome to obtained these plasmas as well as the techniques for quenching them are also reviewed. Last, recent efforts to obtain atmospheric pressure plasmas are discussed with particular emphasis on the capillary plasma electrode discharge, which we have used to obtain high (electron) density nonequilibrium plasmas.

Generation of large-volume, atmospheric-pressure, nonequilibrium plasmas

Due to rapid growth in semiconductor technology, there is a continuous increase of the system power and the shrinkage of size. This resulted in inevitable challenges in the field of thermal management of electronics to maintain the desirable operating temperature. The present paper reviews the literature dealing with various aspects of cooling methods. Included are papers on experimental work on analyzing cooling technique and its stability, numerical modeling, natural convection, and advanced cooling methods. The issues of thermal management of electronics, development of new effective cooling schemes by using advanced materials and manufacturing methods are also enumerated in this paper. .

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Thermal management of electronics: A review of literature

We report the observation and characterization of a new nonresonant strong field ionization mechanism in polyatomic molecules: Nonadiabatic multi-electron (NME) dynamics. The strong field response of a given molecule depends on important properties such as molecular geometry and bonding, the path length of delocalized electrons and/or ionization potential as well as on basic laser pulse parameters such as wavelength and intensity. Popular quasi-static tunnelling models of strong field molecular ionization, based upon the adiabatic response of a single active electron, are demonstrated to be inadequate when electron delocalization is important. The NME ionization mechanism greatly affects molecular ionization, its fragmentation and its energetics. In addition, multi-electron effects are shown to be present even in the adiabatic long wavelength limit.

Polyatomic molecules in strong laser fields: Nonadiabatic multielectron dynamics

This paper presents a complete study of the temporal and spatial characteristics of the preionization of a XeCl rare-gas halide laser. The detailed study was made possible using the technique of laser-induced preionization which utilizes the uv radiation from a KrF laser to preionize a second rare-gas halide laser. In addition to the preionization study, high spatial and temporal resolution framing camera photographs have been used to investigate the growth of discharge instabilities which can lead to the premature termination of the XeCl optical pulse. The roles played by HCl, Xe, the buffer gas as well as the discharge energy loading in the development of discharge instabilities have been determined experimentally.

Preionization and discharge stability study of long optical pulse duration UV-preionized XeCl lasers

The use of volume Bragg gratings (VBGs) recorded in photo-thermo-refractive (PTR) glass for laser beam control is described. These new optical elements provide extremely narrow spectral and angular selectivity and have a high level of resistance to high-power pulsed and continuous-wave laser radiation. These features of PTR volume gratings are used for transverse and longitudinal mode selection, passive coherent coupling, and spectral beam combining (SBC) of semiconductor, solid state, and fiber lasers.

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Spectral Combining and Coherent Coupling of Lasers by Volume Bragg Gratings

A self-sustained volume discharge without preionisation, i.e. a self-initiated volume discharge (SIVD), in nonchain HF lasers with SF6—C2H6 mixtures was investigated. It was established that, after the primary local electrical breakdown of the discharge gap, the SIVD spreads along the gap in directions perpendicular to that of the electric field by means of the successive formation of overlapping diffuse channels under a discharge voltage close to its quasi-steady state value. It is shown that, as new channels appear, the current flowing through the channels formed earlier decreases. The volume occupied by the SIVD increases with increase in the energy deposited in the plasma and, when the discharge volume is confined by a dielectric surface, the discharge voltage increases simultaneously with increase in the current. The possible mechanisms which explain the observed phenomena, namely the dissociation of SF6 molecules and electron attachment SF6 molecules, are examined. A simple analytical model, which makes it possible to describe these mechanisms at a qualitative level, was developed.

Self-initiated volume discharge in nonchain HF lasers based on SF6—hydrocarbon mixtures

Significant stabilisation of self-sustained volume discharges in active mixtures of nonchain HF (DF) lasers was achieved by replacing H2 (D2) with hydrocarbons (carbon deuterides). These discharges were used in chemical lasers with large active volumes and high output parameters. An active volume of 5 litres yielded an output energy of 31 J from an HF laser and 24 J from a DF laser with the technical efficiency of 2.8% and 2.2%, respectively.

Feasibility of increasing the output energy of a nonchain HF (DF) laser

A technique for obtaining a repetitively pulsed operating regime in high-power wide-aperture lasers is proposed and experimentally realised. In this regime, the laser emits a train of pulses with a duration of 0.1 — 1 μs and a pulse repetition rate of several tens of kilohertz. The main properties of the pulsed regime are theoretically analysed and the proposed technique is tested in detail employing a test-bench gas-dynamic laser. The results of the test confirmed the conclusions of the theoretical analysis. The possibility of realising a repetitively pulsed regime in high-power wide-aperture lasers without a reduction in the average output power is experimentally demonstrated.

http://iopscience.iop.org/article/10.1070/QE2003v033n09ABEH002496/pdf

High-frequency repetitively pulsed operating regime in high-power wide-aperture lasers

The conditions under which an optical pulsed discharge stably generates periodic shock waves are determined theoretically and experimentally. It is shown that the mechanism of merging shock waves into a low-frequency quasi-stationary wave is operative in various gases (and vapours) in a wide range of laser spark energies. The application of such a wave for increasing the coupling factor in a laser engine is considered.

Interaction of an optical pulsed discharge with a gas: conditions for stable generation and merging of shock waves

It is shown that a self-sustained volume discharge is possible in mixtures of SF6 with hydrocarbons (or deuterated hydrocarbons) without special devices for the preionisation of the gas. This can be achieved with an extremely compact electrode system. Wide-aperture nonchain HF (DF) lasers with a high output radiation energy can be constructed on the basis of the discharge. It is reported that output energies of 144 J for HF and 115 J for DF were achieved in a system with a 21-litre active medium and an aperture of ~15 cm. The electric efficiencies were 2.8% and 2.2%, respectively.

Victor V. Apollonov

Papers

Self-initiated volume discharge in nonchain HF lasers based on SF6—hydrocarbon mixtures

Feasibility of increasing the output energy of a nonchain HF (DF) laser

High-frequency repetitively pulsed operating regime in high-power wide-aperture lasers

Interaction of an optical pulsed discharge with a gas: conditions for stable generation and merging of shock waves

Nonchain electric-discharge HF (DF) laser with a high radiation energy