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.