Investigation of the excimer lasers

The experimental laser facility named ELA with e-beam excitation of gas mixtures is used in the laboratory to investigate the high power eximer lasers. The purpose of these studies is to identify and solve problems on the way of creation of industrial lasers of this type.

The Experimental e-beam pumped Laser Facility ELA

A high-current electron gun of laser facility ELA has the electron energy of ~300 keV, the total e-beam energy after a foil of electron gun is up to 500 J with a pulse duration of 80 ns and a repetition rate of about 1 mHz.

A large set of studies on the physics of e-beam pumped excimer lasers and laser radiation interaction with different materials has been performed on ELA facility during it operation since 1980.

1. The series of e-beam pumped lasers (EBL) with high specific power and energy of excitation have been launched and investigated on it. These are XeF-EBL (353 nm with the pulse energy up to 5 J in 80 ns), XeCl-EBL (308 nm, up to 6 J), KrF-EBL (248 nm, up to 15 J), ArF-EBL (193 nm, up to 6 J). The laser generation on C-A transition of XeF* molecule has been obtained at photolytic pumping of Ar/Xe2F gas mixture by the radiation of e-beam excimer lamp on Xe2*. Even at the initial stage of ELA facility operation the survivability problem of separation foil of its electron gun has been solved by the use of a multilayer foil from different materials.
2. The possibility of using a KrF-laser radiation for dye lasers excitation on Rhodamine 6G, Coumarin 47, p-terphenyl and POPOP has been studied and the laser energies up to 1 J have been obtained on them.
3. The possibilities of arsenic implantation in silicon using a KrF laser radiation have been investigated.
4. A large number of tests on the radiation strength of mirror and anti-reflective coatings for KrF- and ArF-lasers have been carried out in the development of their production technologies at our Institute, as well as the subsequent implementation of these technologies in a number of other organizations.
5. Working closely with the manufacturers of optical materials for UV and VUV ranges (quartz glasses, MgF2, CaF2, BaF2 and Al2O3 crystals) the behavior of these materials under the action of XeF-, KrF-and ArF-laser radiations as well as the e-beam has been studied. The nonlinear characteristics of a large number of samples of these optical materials at 353, 248 and 193 nm as well as their radiation resistance have been measured. Characteristics of the e-beam induced short-lived absorption of laser radiation have been identified.

   These experimental results have allowed revealing the mechanism of increasing of UV laser radiation absorption in the examined optical materials (OM) due to the appearance of absorption on the short-lived states of the recombination cascade in the OM at their ionization during the laser radiation pulse with duration of more than 1 ns.

6. The behavior of e-beam-induced long-lived absorption in crystals of SiO2, Al2O3, BaF2, CaF2, MgF2 and in high-purity quartz glasses has been studied on the facility “ELA”. Experiments have shown that at a periodic influence of e-beam pulses with the electron energy of ~300 keV and a total fluence F up to~30 kJ/cm2, the induced absorption of the tested quartz glasses KU-1, KS-4V and Corning 7980 as well as of the fluorite with increasing F goes to saturation. The average specific power density of e-beam determines the absorption level. Under the identical exposure conditions a stationary level of absorption in the new Russian quartz glass KS-4V at the range of ~180-300 nm was about 4 times less than that of glass KU-1 and 2 times less than that of the samples of Corning 7980 ArF Grade. In high-purity CaF2 samples the maximum transmission changes under the same conditions of e-beam exposure did not exceed 5-10% at the range of 120-1000 nm. The irradiation of the samples of these optical materials by KrF- or ArF-laser radiation with the intensity of ~5 MW/cm2 both at the time of e-beam influence, and after it reduces the residual absorption in them in 1.5-2 times.

   Thus, it has been demonstrated for the first time that the quartz glasses existing now, first, of KS-4V type, as well as the high purity CaF2 crystals can provide a prolonged and stable operation of repetitively pulsed e-beam pumped KrF-laser windows at insignificant losses of laser radiation energy.

7. A full picture of key defects formation and relaxation in these optical materials at e-beam irradiation as well as at annealing of these defects by UV laser radiation has been revealed analyzing a great number of the induced absorption spectra of various quartz glasses and MgF2 crystals on the basis of their decomposition into individual absorption bands.

The above results have been published in the articles with such key authors as: P.B. Sergeev, N.V. Morozov and A.P. Sergeev. A list of these articles can be found in PUBLICATIONS section.