The constriction of the positive column of a glow discharge in argon was studied both experimentally and theoretically. In experiments the direct current discharge was maintained in a cylindrical glass tube of 3 cm internal diameter and 75 cm length. The voltage–current U(I) characteristics of the discharge were measured at a gas pressure P from 1 to 120 Torr in a wide range of discharge currents. At P > 20 Torr the measured U(I) characteristics display the classical hysteresis effect: the transition from the diffuse to the contracted discharge form (with increasing current) occurs at a current higher than that for reverse transition (with decreasing current). It was also found that in some cases the so-called partially contracted form of the discharge is realized, when the diffuse and contracted forms coexist in the discharge tube.To calculate the plasma parameters under experimental conditions a 1D axial-symmetric discharge model for pure argon was developed. The details of the model are described and the results of simulations are presented. In particular, the electric field strength E in the positive column was calculated as a function of the discharge current. Theoretical E(I) characteristics are compared with those derived from the experiment. For the first time, the detailed kinetic model without the usage of fit parameters predicts the hysteresis effect in pure Ar with parameters of diffuse and constricted forms of the discharge in good agreement with the experiment.

A new quasi-one-dimensional model for a negative corona in air is formulated allowing for the quantitative description of the mechanism of Trichel-pulse formation. Detailed analysis of the processes controlling pulse dynamics is made. Comparison with experiment for a short-gap corona demonstrates a reasonable agreement with the shape of the pulse and in the average characteristics of the negative corona.

The electron energy distribution function (EEDF) in decaying nitrogen plasmas is investigated numerically. The comparison of the calculated and experimentally measured EEDF allows a correction to be made to the cross sectional magnitude for electron scattering from vibrationally excited molecules. The influence of electron-electron (e-e) collisions on the EEDF is investigated. It is shown that e-e collisions may have a strong influence on the EEDF in decaying plasmas even at very low degrees of ionization (2*10-6).

Concentrations of NO, NO 2 , NO 3 , N 2 O 5 , and O 3 were measured by classical absorption spectroscopy in dielectric barrier discharges in flowing O 2 /NO x and N 2 /O 2 /NO x mixtures. The results of measurements in different parts of the discharge chamber and in its exhaust are compared to a numerical zero-dimensional kinetic model and good agreement is found. The experimentally found upper limit of the NO x concentration allowing ozone production is confirmed by the kinetic calculations for both gas mixtures. The rotational temperature of different nitrogen bands was measured by high-resolution emission spectroscopy. The results are explained on the basis of a simplified model and related to the gas temperature in the microdischarge channel and the surrounding gas.

In negative corona discharges in ambient air different discharge modes can be observed. In this paper the discharge current regions corresponding to these modes are determined. The influence of anode geometry, anode resistivity, inter-electrode distance and gas flow on the threshold currents that mark the corona-to-glow and glow-to-spark transitions is investigated. The experimental data are backed up by an analytical treatment of ionization instability development within a local current spot on metallic and resistive anodes.

In this reply we respond to the comment made by E A Bogdanov, M V Krasilnikov and A A Kudryavtsev on our review 'Non-thermal plasma instabilities induced by deformation of the electron energy distribution function'.

We demonstrate that in-phase mode operation with a near-diffraction-limited beam can be realized in large aperture ͑up to 100 elements͒ antiguided vertical-cavity surface-emitting laser ͑VCSEL͒ arrays. A selective etching process with two-step metalorganic chemical vapor deposition is used for fabrication of the antiguided VCSEL array structures. Modal discrimination is enhanced by intentionally choosing a GaAs cap thickness so as to introduce suitable loss to array interelement regions. Far field patterns indicate in-phase mode operation from both triangular and rectangular geometry antiguided VCSEL arrays, which is in good agreement with theory. © 2004 American Institute of Physics. ͓DOI: 10.1063/1.1640799͔Coupled two-dimensional vertical-cavity surfaceemitting arrays are promising as high power ͑more than 10 mW͒ coherent light sources for many applications such as telecommunications, printing, data storage etc. In addition, their two-dimensional periodicity of the gain and index make them ideal sources with which to study the properties of active photonic lattices.1 In the past, much effort has been directed towards realizing coherent emission from phaselocked vertical-cavity surface-emitting laser ͑VCSEL͒ arrays. However, previous work has shown that phase-locked VCSEL arrays tend to lase in the highest-order, out-of-phase, transverse mode. Mode discrimination is also low among various transverse array modes, and generally results in a mixture of high-order modes reaching laser threshold.2 Continuous wave ͑cw͒ operation of 10ϫ10 VCSEL arrays that utilized a metal grid defined structure to insure single higherorder mode operation has been reported. 3 Larger aperture (ϳ138 mϫ138 m) coherent 20ϫ20 VCSEL arrays have been reported previously using photon pumping, and they exhibited a four-lobe, multimode, far-field pattern.4 This behavior is characteristic of evanescent wave coupling in weakly positive index guided or gain guided arrays. 5 To make ''in-phase-mode-like emission,'' external phase shifters are required, although the result is still a relatively broad beam that is indicative of multimode operation.6 Thus, stable, high power, diffraction-limited beam operation has not been realized.Compared to weak evanescent coupling in positive index guided arrays, antiguided structures are attractive due to the strong leaky-wave coupling between each element in the array. What is more, modal discrimination is also enhanced by array mode dependent lateral radiation loss. Thus, by properly choosing the index step and width of the coupling region, the in-phase array mode is favored to lase. Moreover, antiguided arrays are less vulnerable to thermal lensing and gain spatial hole burning ͑GSHB͒ because of the strong built-in index step, which leads to stable beam operation at high output power. 7 In 1999 Serkland et al. reported the observation of in-phase mode emission from two leaky-wave coupled VCSELs. 8 Later, in 2000, diffraction-limited emission from two-dimensional ͑2D͒ (4ϫ4) leaky-wave coupled VCSEL arrays 9,10...

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