This paper reports on the creation of a THL-100 multi-terawatt hybrid laser system based on a Start-480M titaniumsapphire starting complex and photochemical XeF(C-A) amplifier with a 25-cm aperture. The complex produces 50-fs radiation pulses of energy up to 5 mJ at a second harmonic wavelength of 475 nm. The active medium of the amplifier is created in a XeF 2 /N 2 mixture under vacuum-ultraviolet radiation of electron beam-excited xenon. The results of first experiments on femtosecond pulse amplification in the active medium of the XeF(C-A) amplifier are presented to demonstrate that a laser beam peak power of 14 TW has been attained.

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Optically excited active medium at XeF(/4) transition (X = 481 nm) is considered from the viewpoint of its possible application in ultrashort (down to 10 fs) light pulses amplification due to the extremely wide amplification band of the transition. Photolytical pumping of XeF(C -A) by pulsed discharge or shock wave radiation allows one to amplify light beams with the cross-section at least up to -1 m 2 . Taking into account strong bulk and surface nonlinear effects at high-power density, it seems feasible to get the output energy up to ~ 1 kJ and the power density in the focal spot up to 10 23 W/cm 2 . Consideration of spatial-time distribution of the excited XeF(C) molecules, formed in the XeF 2 photodissociation wave under the action of powerful optical pumping, shows a possibility in principle to design multipass amplifiers with the inversion running wave, which are intended for the amplification of ultrashort pulses up to the energies noted above.

The three-step three-color laser population of the I2(β1g, νβ, Jβ and , νD, JD) rovibronic states via those of the and 1u, (bb) states, correlating with the second and third dissociation limits of the valence states, has been used for the study of mechanisms of optical transitions involved in the population of the β1g, νβ, Jβ rovibronic states. It has been shown that the 1u(bb) ←  transition is allowed due to hyperfine interactions of the 1u(bb), ν1u, J1u and (bb), ν0, J0 rovibronic states, though energy gaps between these pairs of the states are huge, greater than 0.7 cm−1. The ΔJ = ±2 lines observed in the β1g − 1u(bb) transition are also due to hyperfine interaction of the 1u(bb), ν1u, J1u and (bb), ν0, J0 rovibronic states. It has been also shown that the 1u(bb) ←  transition cannot be attributed either to magnetic dipole or to electric quadrupole transitions. Contributions from the Stark effect in a strong laser field and from possible production of the I2(X)… I2(B) colliding pairs to mechanism of the 1u(bb) −  transition are negligible.