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1

Photoelectron emission and its instrumental effect on optogalvanic measurements in a hollow cathode discharge

Zhechev D., Bundaleska N., Costello J. T., Todorov D.

Opto-Electronics Review

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2005

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Vol. 13, No. 3

193-196

EN

The photoelectron emission (PE) from the cathode surface of a hollow cathode discharge (HCD) with a sub-breakdown bias applied, and hence no discharge present, was measured within the framework of an optogalvanic (OG) experimental arrangement. The work function dependence on the applied sub-breakdown voltage was investigated. The PE component in a real OG measurement was found to manifest itself as an instrumental effect together with nonresonant ionization which we call here space ionization (SP). The convolution of these components was determined experimentally as an instrumental function. A deconvolution procedure to determine the actual OG signal was developed.

2

Diagnostyka ośrodków laserowych i wyładowczych na mieszaninach gazów szlachetnych i par metali

Adamowicz T. M.

Prace Naukowe Politechniki Warszawskiej. Elektronika

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2003

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z. 146

3--128

PL

Praca obejmuje przegląd badań ośrodków laserowych na mieszaninach gazów szlachetnych i par metali wytwarzanych w wyładowaniu wnękowym. Szczególną uwagę poświęcono diagnostyce laserów tego typu. Opracowano unikalną metodę pomiarów wszystkich parametrów laserowych ośrodka, tj. wzmocnienia nienasyconego i nasyconego oraz ich rozkładów przestrzennych, parametru nasycenia, a także strat optycznych w rezonatorach laserowych. Prezentowana metoda umożliwia precyzyjne porównywanie ośrodków wytworzonych w różnego typu katodach wnękowych dla różnych rodzajów pobudzania. Stosując ją, przeprowadzono badania wnękowych laserów jonowych ważnych dla generacji ultrafioletu. Wyniki pomiarów parametrów laserowych i plazmowych zostały wykorzystane do ilościowego opisu zjawisk prowadzących do generacji laserowej. Opracowano i rozwinięto nowatorską metodę wyznaczania współczynników dyfuzji atomów metali w gazach szlachetnych, która może zastąpić lub uzupełnić dotychczas stosowane metody spektroskopowe. Dzięki nowej metodzie określono szereg, dotychczas nieznanych, współczynników dyfuzji atomów metali, m.in. Au i Ag w He oraz Ag i Zn w Ne. Zapoczątkowane przez autora badania wpływu lżejszego izotopu He3 na parametry laserowe oraz plazmowe zaowocowały znaczącym wzrostem mocy i sprawności generacji laserowej na mieszaninach gazów szlachetnych w ośrodkach wytworzonych w wyładowaniu wnękowym. Podobnej poprawy parametrów laserowych należy oczekiwać także w przypadku laserów jonowych na parach metali (He-Cd i He-Se), w których wykorzystuje się kolumnę dodatnią wyładowania. Badania wyładowania Townsenda w mieszaninach Ne-Ar przy użyciu laserowego efektu optogalwanicznego (OGE) doprowadziły do odkrycia kataforezy, której istnienia nie podejrzewano w tym typie wyładowania. Analityczne modele wyładowania Townsenda oraz zjawiska optogalwanicznego opracowane dla tego wyładowania, umożliwiły wyznaczenie z dostateczną dokładnością całkowitego współczynnika jonizacji w mieszaninach Ne-Ar oraz wielkości sygnałów OGE.

EN

This work presents the results of researches on lasing and discharge plasma media created in noble gas and metal vapour mixtures. Special interest was given to sputtered metal ion lasers operating in hollow cathode discharges (HCD). The study of the HCD laser features were performed by using anovel diagnostic method for measuring alllasing parameters in such lasers. Unsaturated and saturated gain, its spatial distribution, saturation intensities and optical losses in laser resonators were measured for several HCD sputtered metal ion lasers with different hollow cathode configurations. The obtained results were used in modelling laser action in He-Au and He-Cu lasers. An unique method was invented and developed to determine diffusion coefficients of metal atoms in noble gases. Employing this method the diffusion coefficients of several metals in He and Ne were found, some of them, e.g Au and Ag atoms in He as well as Ag and Zn atoms in Ne, have never been reported before. The influence of helium He3 isotope on plasma and laser parameters in He - noble gas and metal atom mixtures excited in HCD was investigated. A significant increase in gain, output power and efficiency of the laser operation was achieved for He-Kr, He-Ar and He-Ne lasers. Townsend discharges in Ne-Ar Penning mixtures were studied by using the optogalvanic effect (OGE). A strong cataphoresis was observed though this phenomenon had never been thought to occur in this kind of discharge. An analytical model of the OGE based on rate equations for Ne(ls2-s) states population together with electron production term for this discharge was elaborated. The model was used to calculate total ionisation coefficients in Penning mixtures and intensities of OGE signaIs in a wide range of Ne-Ar pressures and Ar admixture.

3

Radial inhomogeneity in a shape of spectral line emitted from hollow cathode discharge

Parvanova N.

Opto-Electronics Review

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2003

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Vol. 11, No. 4

345-347

EN

The Lorentzian width of the spectral line Hel 504.7 nm emitted in the negative glow of a hollow cathode discharge (HCD) was found to increase depending on the distance from the emitting volume to the cathode axis. This effect manifests itself at low buffer gas pressures pHe E[epsolon](0.0-0.28) Torr. The later is typical for the experiments on SFS, radiative width and other constants. Thus, the observed radial inhomogeneity concerns the accuracy of these measurements. It is checked by determination of radiative width of the Hel 504.7 nm line emitted by two regions along the radius of HCD.

4

Excitation space anisotropy, coherence and coherent conductivity in hollow cathode discharge

Zhechev D., Parvanova N.

Opto-Electronics Review

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2003

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Vol. 11, No. 1

51-54

EN

Based on the excitation space anisotropy a partial polarisation of the spontaneous emission is found in hollow cathode discharge. This polarisation is ascribed to existing spontaneous coherence, i. e., self-alignment of the excited states. The aligning factors are the beam-like fast electrons from the cathode dark space. An expression for observed signal of the spontaneous emission magnetic depolarisation is obtained. Withim the frames of the ordinary opto-galvanic effect a separate coherent conductivity is analysed. a poor coherent conductivity due the self-aligned states is detected.

5

Anomalous optogalvanic signal : spectrometric applications

Zhechev D., Parvanova N.

Opto-Electronics Review

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2003

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Vol. 11, No. 1

31-34

EN

Along with the conventional optogalvanic (OG) signal an anomalous ligh-induced response has been detected in hollow cathode discharge. This response manifests itself both in the amplitude and time-resolved OG reactions. The anomalous OG signal is found to be less dependent on the absorbing optical transition and yet, more informative on the parameters of the plasma medium, that is the OG detector. This circumstance is proposed for usage in four applications based on the behaviour of the anomalous OG signal. The latter is taken as a spectral marker, as an amplified quasi-amplitude signal as well as a sensitive tool in monitoring procedure.

6

A hollow cathode discharge modification as a of sputtered atoms and their ions

Zhechev D., Tileva S., Mishinsky G. V., Zhemenik V. I.

Opto-Electronics Review

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2001

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Vol. 9, No. 4

419-422

EN

A nonconvectional hollow cathode discharge (HCD) modification grounded on a conical bottom (CB) cylindrical cathode is reported. this CBHCD enhances the main HCD property, i.e., the sputtering of the cathode surface/probe inserted. Comparative polarisation measurements with a conventional flat bottom HCD show a stronger narrowing of the Hanle signal width for the sputtered Cu atoms in CBHCD.This their density is higher in CBHCD. This result is specified by the redial optogalvanic profile. It contains two peaks of the mentioned density, i.e., near the cylindrical cathode surface and over the cone peak. Some preliminary examinations of CBHCD as an ion source in three arrangements are performed and discussed.