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Ultraviolet Radiation Source

#1378


High Power Ultraviolet Sources

Tech Area / Field

  • PHY-OPL/Optics and Lasers/Physics

Status
3 Approved without Funding

Registration date
13.10.1998

Leading Institute
Vavilov State Optical Institute (GOI), Russia, St Petersburg

Collaborators

  • Technische Universität München, Germany, Munich\nUniversity of Uppsala, Sweden, Uppsala\nABB Corporate Research Ltd, Switzerland, Baden\nUniversity of Toledo, USA, OH, Toledo

Project summary

The urge to create new sources of ultraviolet (UV) radiation arose mainly from the needs of microelectronics, metrology, ecology, byology, medicine, etc. Here we mean hard UV radiation sources emitting in the wavelength shorter than 200 nm, that is in the so called vacuum UV region where it is necessary to place optical devices in vacuum because of the absorption of the atmospherical gases. Recent publications testify that molecules of the heavy rare gases (argon, krypton, xenon), both homo- and heteronuclear, are very promising emitters in the spectral region 110-200 nm (neighbouring the vacuum UV region), and that electric discharges are efficient way of exciting the spectra of these molecules. Investigations of the rare gases molecules with the purpose to develop both coherent and noncoherent UV radiation sources are going on in USA, Canada, Germany, Switzerland, Sweden, France, Japan, Russia etc.

The rare gases molecules are typical excimers (excited dimer), that is their ground states are weakly bound, and these molecules may easyly be split in atoms by chaotic collisions. Optical transitions from the bound excited states of excimer molecules to their ground states result in bands of continious radiation (continua), and jointly continua of the rare gases cover the spectral interval 110-200 nm. As to the known UV sources which emit in this interval and utilize an electric discharge to excite the rare gas, the population of the emitting excimer states is a result of a sequence of atomic-molecular processes, the last components being a conversion of excited atoms to excited molecules. The authors of the present project discovered a new mechanism of creating excimers which becomes very efficient when the gas discharge plasma is cooled down to a temperature near gas condensation. In this case the concentration of the weakly bound ground state molecules increases sharply, and direct excitation from the ground state by electron impact becomes efficient. Hence the creation of excited molecular states is being realised in a single step.

The purpose of the present project is to create laboratory models of the sources (for the interval 110-200 nm) using the new mechanism for creating excimers and to determine their ‘extremum’ parameters. We intend to use three types of electric discharges - a dc discharge, a multichannel diffuse discharge, and a barrier discharge - each suited for the supposed future use of the sources.

The authors of this project believe that the proposed approach will allow us to increase the efficiency of the sources without considerably complicating their technical realisation, and to develop a new series of spectral lamps for pure and applied investigations. Besides it will provide a foundation for creating a cw (continious in time) laser of the wavelength ~ 147 nm.

Investigating the atomic-molecular processes in a deeply cooled plasma is a necessary and extremely important stage in developing the sources. This information may be obtained by a exploring in detail the rare gas spectra as functions of excitation parameters and gas mixture. In particular we intend to study and to exploite actively the mechanism of excitation energy transfer in rare gases mixtures. The spectral density of radiation may be increased sharply by transferring excitation energy to the excimer states which will then emit in a narrow band.

Experimental investigations will be supported by calculations of both excimer molecules emission spectra and plasma parameters taking into account both homo- and heteronuclear rare gas molecules. Our experience in the field of gas discharges, as well as fundamental and applied atomic and molecular spectroscopy will be used in the project. In particular our “know-how” protected by patents will be used.

The following results are supposed to be derived when carrying out the project.

1. A physical model of the processes taking place in a rare gas plasma discharge cooled cryogenically will be created based upon the results of both experimental and theoretical studies. The model will take into account all the main channels of population of the excimer states including both direct excitation from the weakly bound ground state and excitation transfer in rare gas mixtures. The constants of the processes will be determined.

2. Using the physical model, laboratory models of the sources will be designed and examined for the spectral interval 110-200 nm and herein the new mechanism of creating excimers will be efficiently used. We intend to design new sources which are more efficient than exsisting sources and to improve the spectral characteristics of radiation that is important for applications.

3. The efficiency of the new sources will be examined when using them for the most interesting applications. In particular, barrier lamps of special design will be used to disinfect water, for the photodestruction of metal containing mixtures, and for other technologies where at present moment lamps containing mercury are being used. We expect to design lamps with higher efficiency and be able to substitute mercury lamps by ecologically harmless ones filled with rare gases.

4. Gain coefficients in long plasma columns generated by a dc discharge, by a multichannel diffuse discharge, and by a barrier discharge (wavelength ~ 147 nm) will be measured.

5. A cw laser (wavelength ~ 147 nm) will be designed and radiation parameters will be examined experimentally.

Role of foreign collaborators: The project is supported by the Uppsala University (Uppsala, Sweden), Technical University (Munich, Germany), The University of Toledo (Ohio, USA), ABB Corporate Research Ltd (Baden, Switzerland). We intend to discuss the results of the project jointly with the centres mentioned above. Some of the project stages will be fulfilled using experimental equipment of Uppsala University.


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