Pulsed Gas Lasers Based on SOS-Diodes
Pulsed Gas-Discharge Lasers with Pumping from Inductive Energy Store with Semiconductor Opening Switch
Tech Area / Field
- PHY-OPL/Optics and Lasers/Physics
- PHY-PLS/Plasma Physics/Physics
8 Project completed
Senior Project Manager
Lapidus O V
Siberian Branch of RAS / Institute of High Current Electronics, Russia, Tomsk reg., Tomsk
- VNIITF, Russia, Chelyabinsk reg., Snezhinsk
- Department of the Navy / Naval Research Laboratory, USA, DC, Washington
Project summaryThe goal of the Project is to develop ultraviolet gas lasers on the basis of the latest achievements of the Project participants in the field of powerful pulsed equipment and physics of pulsed gas discharges.
The principle goals of the Project are the following:
– to develop a new type of gas media pumping source on the basis of completely solid generators with inductive storage of energy and semiconductor opening switch;
– to optimize the regimes of consistent energy transmission from inductive store with semiconductor opening switch into gas discharge loading;
– to build several pilot samples of ultraviolet gas lasers with new type of pumping source which differ by power and wave length of radiation (small-size nitrogen lasers with wave length 337.0 nm and radiation energy from 10 100 to 100 MJ, pulse repetition rate from 1 up to 1,000 Hz; pulse excimer lasers with wave length from 248.4 up to 351.0 nm and radiation energy from 100 MJ at a small aperture up to 10 J with wide-aperture version).
The experience of development of laser technologies show that for some problems, it is necessary to apply pulse ultraviolet radiation with high peak and/or medium power. Gas lasers meet most completely these problems, in particular the lasers on nitrogen molecules and exiplex molecules. These lasers having high generation threshold are easy-to-excite by powerful volume charges, generate pulse ultraviolet radiation with relatively high efficiency, can work in frequency regime.
In order to excite such lasers, it is necessary to provide small rise time and high specific power of pumping pulse; in order to achieve high efficiency, pulse duration on the whole is not to exceed optimum. Using traditional equipment to generate pulses of current and voltage based on capacitive store and spark gaps, it is difficult to meet these requirements due to design inductivity of discharge loop. Because of high inductivity, pumping of lasers with wide aperture is especially difficult, where distance between electrodes can be tens of centimeters. In order to excite lasers, various complicated schemes of pumping were applied, for example, schemes with double loop, schemes with sharpening spark gaps and others.
In lasers with high generation threshold and small time of existence of inverse population which are nitrogen and exiplex lasers, it is promising to use inductive stores of energy with fast opening switches. Inductance of discharge loop is used as the main element of pumping generator – energy store, that leads to increase of pulse power of pumping. Design location of opening switch directly on electrodes of laser interval permits to decrease up to minimum loop inductivity that leads both to decrease of rise time and increase of the power of this pulse. Powerful pumping pulse formation is facilitated by the fact that when fast opening switch is operated, the amplitude of generated pulse of voltage increases by a factor of 3-5 in comparison to charge voltage of initial store. However, currently, there is no opening switch applicable to using in schemes of gas laser pumping.
Within recent 10 years, we discovered and investigated the effect of dense current interruption in semiconductor devices. It was called SOS-effect (SOS - semiconductor opening switch), and the devices built on its basis – semiconductor opening switches were called SOS-diodes . Such switches unlike exploded wires or plasma switches provide the pulse repetition rate up to 1,000 pps at switched power: medium – up to tens kW and peak - up to units of GW. Besides, SOS-diodes have high stability of operation that provide repetitive mode of generated pulses. Currently, several pulse generators were built on the basis of SOS-effect having wide range of parameters .
In this Project, it is proposed to develop new type of gas medium pumping source on the basis of generator with inductive store and SOS-diodes to generate radiation both in small-size lasers and in lasers of wide aperture. Generators on SOS-diodes permit to optimize the duration and amplitude of pumping pulse for specific core that increases the efficiency of the whole device. It is the use of SOS-diodes as the opening switches having small sizes and located directly on electrodes of discharge gap that permits to build wide-aperture lasers with high pulse power at the cost of decrease of pumping loop inductivity. The effect of voltage pulse amplitude increase with current cutoff by SOS-diodes permits to use low charge voltage of initial store. Fast recovery of SOS-diodes permits to use them for generation of pulses with the pulse repetition rate higher than 1,000 Hz.
New systems of pumping always caused new turn in the development of laser equipment. Thus, our Project is directed to the development of physical and technical foundations of building powerful equipment of generation of laser radiation with high peak and medium power on the basis of SOS-effect. The samples of lasers built as the result of Project performance will be the prototypes for subsequent reproduction and application in different areas of science, industry and medicine, for example:
– laser modification of the surface for laser annealing of semiconductors and nano crystals in particular;
– laser cutting of micro elements;
– investigation in the field of photo- and laser chemistry and CVD-processes;
– microsurgery, including ophthalmology.
For mentioned applications, in the frames of the Project, the following pilot samples of lasers will be built:
– repetitive nitrogen lasers with wave length 337.1 nm and radiation energy from 10 up to 100 MJ, pulse repetition rate from 10 up to 1,000 Hz;
– pulsed exiplex laser with radiation wave length from 248.4 up to 351.0 nm and radiation energy higher than 100 mJ;
– wide-aperture exiplex laser with radiation wave length 308.0 nm and energy in the pulse up to 10 J.
Competence of the Project participants corresponds to the placed task. In order to perform the Project, various scientists were united. In their pioneer efforts, they:
– discovered and investigated SOS-effect;
– developed and built SOS-diodes;
– built high voltage pulsed generators on the basis of SOS-effect with wide spectrum of parameters;
– established the regularities of forming independent space discharges for gas laser pumping.
The key condition of successful performance of the Project is the use of scientific, technical and production potential of VNIITF and IEP UD of RAS where they accumulated rich investigation experience in the field of pulsed power equipment, formation of independent volume discharges and laser radiation. Besides, in these institutions, unique experimental equipment is available whose using in the frames of the Project will simplify its performance.
The main expected result of the Project is to create a mock-up of UV laser sample with new type of pumping generators, including wide-aperture laser. To achieve the result, pulse generators will be built on the basis of inductive stores with SOS-diodes, the issues of effective energy transmission from inductive stores into gas discharge plasma will be studied, characteristics of radiation of UV radiation of nitrogen and excimer pulsed gas lasers will be investigated.
Application of this result will permit to create up-to-date types of gas lasers and will serve the basis for investigations on laser technologies. These efforts will provide occupation of weapon scientists-participants of the Project on commercial basis.
Realization of proposed Project perfectly meets the ISTC goals and objectives:
1. VNIITF nuclear specialists and engineers will have unique opportunities to redirect their talents to the development of high-tech products.
2. Scientists of IEP will have the opportunity to realize their scientific developments in actual devices.
3. US leading specialists participation in the Project as collaborators will facilitate the involvement of Project participants into international scientific community.
The scope of activities is determined by the necessity to solve the main tasks of the Project. They are: creation of generators of pulsed voltage with different parameters; investigation of regimes of consistent energy transmission from inductive stores into plasma of volume discharges; investigation of the influence of parameters of pumping generators and characteristics of a core on laser radiation, especially in wide-aperture laser.
Solution of these problems is made in parallel with the following splitting by years:
1st year – the development and creation of generators of pulsed voltage on the basis of inductive stores and semiconductor opening switches; creation of small-size nitrogen lasers;
2nd year – creation of excimer small-size and wide-aperture lasers and investigation of their characteristics;
3rd year – creation and refinement of the working models, development of pilot samples of gas discharge lasers.
Role of foreign collaborators consists of the consultation at the stage of the Project preparation, exchange of information on the topic of the Project, expertise of obtained results, participation in the technical verification of the Project activities, conducting joint workshops and support in commercial realization of the Project results.
Originality of technical approach and methodology of the Project consists first of all of the following:
1. In order to excite gas media, generators of pulsed voltage on inductive stores with SOS-diodes will be used.
2. Complex character of investigations of the processes in plasma of gas discharges, including experimental study of the processes of consistent energy input into the plasma of discharge, its transformation into coherent radiation as well as numerical methods of studying the processes in radiating plasma will be realized.
3. For the first time, in exiplex wide-aperture laser, pumping generator will be used with SOS-diodes that will open the possibility to create powerful (higher than 10 kW) UV lasers working in repetitive mode.
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