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Efficiency Improvements in Excimer Lasers

#1754


Research into Ways to Increase the Efficiency of Short-Pulse Excimer Lasers with E-Beam Pumping

Tech Area / Field

  • PHY-OPL/Optics and Lasers/Physics

Status
3 Approved without Funding

Registration date
23.12.1999

Leading Institute
NIIEFA Efremov, Russia, St Petersburg

Supporting institutes

  • VNIIEF, Russia, N. Novgorod reg., Sarov\nRussian Scientific Center of Applied Chemistry, Russia, St Petersburg\nTRINITI, Russia, Moscow reg., Troitsk

Project summary

The basic purpose of the project is the development of ways for increasing of the total efficiency of excimer lasers with e-beam pumping of active media at receiving of radiation pulses with duration from units up to hundreds ns.

Excimer lasers on halide of inert gases are one of the main candidates in drivers for thermonuclear reactors with inertial confinement of plasma. The elaboration of large-aperture KrF-amplifying modules are carrying out in large physical laboratories of the world, that is caused by their known advantages: directly received small wavelength and low coherence of radiation, high internal efficiency of active medium, relatively cheap, оptically homogeneous gaseous active medium convenient for the realization of operating mode with pulse repetition.

As is known, for receiving of economically favorable balance of energetic reactor the laser driver should have the total efficiency not less than 5% at generation of radiation pulses with the duration of 5-10 ns, that essentially exceeds the efficiency of modern large installations. Thus, the search of ways for increasing of efficiency of ns-excimer laser installations is represented nowadays rather urgent.

Because of small time of spontaneous decay of upper levels of excimer media in comparison with media of other types modern thermonuclear excimer installations of ns-range pulse duration are constructed on scheme of the generator - amplifier with use of systems of compression and decompression of amplified pulses. In this case it is possible to achieve relatively high efficiency of large-aperture amplifiers with pumping of medium by transverse electron beams. The numerical modeling of such amplifiers shows an opportunity of the further improvement of their characteristics. Therefore in the present project as the first direction of works the development of computing codes for stricter and exacter complex optimization of large-aperture KrF-amplifiers and the elaboration of its projects for revealing of technical difficulties which can arise at their realization.

The necessary check of the technical decisions for future reactor drivers can be carried out on installations of small and average scale capable to work with frequency of pulse repetition of 10-20 Hz. In this case an opportunity of their independent use in various technological applications in processing, electronic and other industries appears. The increase of efficiency of such installations also is the important task, but it is not so much from the scientific point of view, as from economic one. In connection with told in the present project the second direction of works - continuation of the development of compact pulse-periodic excimer lasers with transverse e-beam pumping of the type "Lira" is planned.

In last years an interest to generation of high power laser pulses of super-short duration has strongly increased. The similar systems represent large interest for fundamental researches of interaction of super-strong light fields with substance and for applied tasks too. In particular, rather new schemes of ignition of thermonuclear targets in the problem of IFC were recently offered, in which together with ns- laser pulses carrying the main part of energy, light pulses of ps-duration are proposed for using. The similar schemes allow essentially to lower the requirements to output energy level of the laser driver and consequently are deserved serious complex studies.

It is necessary to emphasize, that the physics of e-beam pumping of laser active medium for times, smaller time of spontaneous decay of upper levels of exited halides and dimers of inert gases, and also physics of amplification of super-short high-intensive pulses of radiation in many respects is not even clear. If at numerical modeling of large-aperture exciplex lasers and amplifiers quasi-stationary approach is usually applied, in this case non-stationarity of processes of interaction between electron beams at high density current (1 kA/cm2) and gases at pressure 1 аtm and kinetic processes developing in active medium will have determining influence on the physical picture as a whole and on total efficiency of laser system, in particular. Told has defined the third direction of works under the present project, which has more fundamental importance, than applied one, and the received results can create the basis for preparation of subsequent proposals.

Four scientific institutions which have prepared the present project, have decided to unit efforts in searches of ways for increasing of total efficiency of excimer lasers with e-beam pumping at receiving of short pulses. Thus the use of scientific and technical starts available at disposal of teams of participating organizations, including on complex numerical modeling of excimer lasers (NIIEFA, ТRINITI), development of methods of formation and amplification ns-pulses of laser radiation (ТRINITI, RSC PH), numerical modeling of interaction between electron beams and solid/gas media (NIIEFA, ТRINITI), experimental improvement of methods of excimer media pump with using of transverse and longitudinal electron beams (ТRINITI, NIIEFA, VNIIEF, RSC PH), researches of plasma-chemical processes, occurring in excimer media at e-beam pumping (RSC PH, VNIIEF), and also on designing and creation of excimer lasers, including ones with pulse repetition (NIIEFA, TRINITI, RSC PH) is supposed.

Proceeding from a general purpose, taking into account the opportunities and experience, each participating institution plans to carry out coordinated numerical and experimental researches, joint analytical discussions of results of these researches and the elaboration of the scientific recommendations on increase of total efficiency of excimer lasers with e-beam pumping, capable to work both in single pulses and pulse-periodical operating modes. These recommendations will be taken into account at the elaboration of the project of 1кJ 10 Hz excimer laser for technological applications and technical proposals on creation of large-aperture multi-kilo-joule KrF-excimer amplifier of short pulses for physical researches, including ones on the problem of ICF.

Distinctive features of proposed elaboration, distinguishing it from similar works in other scientific centers, are more high density of accumulation and more high efficiency of transformation of energy in all systems of lasers, that allows to create compact and effective installations capable to work in pulse repetition mode.

The main technical approach to achievement of posited purpose consists in development of computer codes, numerical modeling and self-coordinated numerical optimization of physical processes of energetic pumping of active medium in excimer lasers and amplification of light ns-pulses, and also in carrying out model physical experimental researches for check of theoretical predictions and proposals on increasing of efficiency both separate systems, and lasers as a whole and using of these proposals at the elaboration of concrete projects.

Development of computing codes is understood as the research and the account in numerical programs of such factors as nonstationarity and spatial nonhomogeneity of e-beam pumping of active medium, nonstatonarity of kinetic processes, developing in it and also coherent interaction of short pulses of amplified radiation with medium in various operating modes, including in the mode of running wave. Besides for more complex modeling of lasers the codes for the calculation of processes of generation and formation of electron beams, passage by them piding foils and supporting structures of accelerator vacuum diodes will receive the development also.

The experimental researches will be carried out on existing or modernized installations:


· Excimer lasers "Lira-1М" (1kJ, 500 ns), "Lira-01" (0,1 кJ, 500 ns, 20 Hz) with transverse pumping by contrary electron beams - NIIEFA;
· Excimer laser "Malish" (0,03 кJ, 30 ns) with longitudinal e-beam pumping - RSC PH;
· Subnanosecond laser bench ТL-2 - ТRINITI;
· Electron accelerator "Straus-2М" (3 МeV, 100 кА, 20-40 ns) - VNIIEF;
· Electron accelerator "Neva-L" (1МeV, 100 кА, 80 ns) - NIIEFA.

These installations in a complex create the wide opportunities for researches of various active media, conditions of their excitation and output of laser energy in pulses of various duration. The electron accelerators "Straus-2М" and "Neva-L" will be used basically for realization of model physical researches, while excimer laser "Lira-01" - for improvement of the technical decisions, which will be used in the more high power pulse-periodical laser "Lira-1".

The present proposal basically should be attributed to a category of applied researches. Executed on the basis of results of numerical and experimental researches the elaboration of the technical proposal on creation of large-aperture multi-kilo-joule KrF-amplifier could serve as the Russian contribution to international cooperation in area of ICF. The created project of 1 кJ 10 Hz excimer laser could make a basis for creation jointly with collaborators and other foreign organizations the technological 10 kW laser installation. The received results on the third direction of works could be used for preparation of the new projects to ISTC, having applied significance and connected with development of short-pulse e-beam pumped excimer lasers of UV and VUV-ranges of spectrum.

The submitted project will bring the contribution in performance of the ISTC purposes, namely:


· In preservation of the high-professional staff in participating scientific organizations.
· In development of conversion activity of these organizations and creation of new laser engineering for scientific researches and high technologies.
· In involving the Russian scientists involved before in development of weapons, in international scientific and technical cooperation in the peace purposes.

The Russian participants are interested in cooperation with foreign collaborators on the following positions:


· Exchange of the scientific and technical information during realization of the project;
· The help in commercialization of results of works, including elaboration of 10 kW pulse-periodic excimer laser;
· Rendering of assistance to the participants of the project in visiting of international meetings on given and related themes.

Carrying out of joint symposiums and working meetings.


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