Detailed studies of charge exchange pumping of ions in femtosecond laser-produced plasmas colliding with a pulsed gas jet are presented. Strong selective excitation of XUV ionic transitions in the reaction C4++H→C3++H+ is observed. Dependences of line intensities on various experimental parameters are reported which are in good agreement with the theory of charge transfer processes. Analyses of experimental data provide evidence that an efficient charge exchange pumping is realized at densities of reagents well in excess of 1016 cm−3, which is essential for the realization of XUV lasers. In preliminary investigations of the reaction C6++H→C5+ (n=3,4)+H+ a strong increase of line intensities at 13.5 and 18.2nm is reported. Analysis of lasing in Na-like ions with an example for Chlorine promises even more efficient pumping as compared with the before analyzed hydrogen like ions.

Short pulse laser generated plasmas interacting with a pulsed gas jet are studied to aid the realization of novel XUV laser schemes based on recombination supported by charge exchange pumping. Interaction of C 4+ , O 3+ and O 4+ ions with hydrogen and nitrogen indicates strong charge exchange pumping of C 3+ (3p-2s, 3d-2p) lines at 31.2 and 38.4 nm, and O 2+ (2p 3s-2p 2 ) and O 3+ (2s 3d-2s 2 2p) lines at 37.4 and 23.8 nm.

Summary form only given. With intense short laser pulses highly ionized plasmas can be generated that allow the realization of lasers in the XUV spectral range. The needed population inversion in the studied systems is generated by the recombination of ions and electrons. Here we will present investigations on plasmas, starting from gaseous targets (gas jet) and targets consisting of particles and clusters produced by ablation mechanisms. For the ionization a 100 fs titanium sapphire laser is used, while the ablation from solid targets is performed by a ns Nd:YAG laser. It is shown that for atomic gas targets optimum conditions for possible lasing transitions are obtained with the shortest pump pulses (100 fs). In contrast, particle and cluster targets require longer pulses (ps-range). This indicates different involved ionization mechanisms like multiphoton- and optical field ionization (OFI) for the short pulses and cluster ionization with Coulomb explosion for the longer pump pulses. Specifically, short laser pulse ionization of oxygen gas and low ionized lithium ablation preplasmas are compared. For the O/sup 2+/(2p3s /spl rarr/ 2p/sup 2/) transition at 37.4 nm, where gain was already observed, the line intensity strongly decreases with longer laser pulse duration (at a constant pulse energy), while for the Li/sup 2+/(3d /spl rarr/ 2p) transition at 72.9 nm the line intensity increases with longer laser pulses. This is attributed to cluster ionization effects in lithium plasmas. Experimental attempts to obtain gain at 72.9 nm will be presented.

The interaction of a femtosecond laser-produced ablation plasma with a pulsed gas jet is studied. XUV spectroscopic investigations show that charge-exchange excitation due to the reaction C4+ + H → C3+ (n = 3) + H+ takes place in the interaction region. The dependence of line intensities on different experimental parameters is studied. At optimum conditions, the 3p–2s transition of C3+ ions at 31.2 nm wavelength shows an increase of up to four times in the line intensity which is induced by the gas jet at a backing pressure of 100 mbar at a distance of 1 mm from the target surface, while transitions from the n = 4 and higher levels decrease. Preliminary experiments with an Al2O3 target show even a tenfold increase in intensity of the 2p3s–2p2 line (λ = 37.4 nm) of O2+ ions.

A charge transfer pumping as a possible tool for lasing in XUV is investigated in the Institute of Laser Physics, Novosibirsk. A new scheme based on the laser-produced plasma colliding with the laser-evaporated gas was previously proposed and tested. It showed that lasing at 52 nm can be achieved on the 4-3 transition of Li-like O+5 ion. Preliminary results on the enhanced emission at 50 nm and on the specifics of charge transfer reaction O+6 + H-2 --> O+5 + H+ are reported.

A charge transfer pumping as a possible tool for lasing in XUV is investigated in the Institute of Laser Physics, Novosibirsk. A new scheme based on the laser-produced plasma colliding with the laser-evaporated gas was previously proposed and tested. It showed that lasing at 51.2 nm can be achieved on the 4-3 transition of Li-like O+5 ion. Preliminary results on the enhanced emission at 50 nm and on the specifics of charge transfer reaction O+6 + H-2 --> O+5 + H+ are reported.