Measurement of a subpicosecond coherence time in a quasi-steady-state XUV laser

We have carried out a detailed characterization of the temporal coherence and spectral bandwidth of the Ne-like Zn XUV laser, collisionally pumped in the quasi-steady-state (QSS) regime and operated at saturation. The measured coherence time τc=680±70 fs is significantly shorter than previously observed with other types of collisional XUV lasers, using the same measurement technique. Additional measurements performed below saturation were used to investigate gain narrowing of the spectral width of the lasing line. Our experimental data are well reproduced by calculations performed with a one-dimensional radiative transfer numerical code, taking the measured gain as an input. We show that our results are consistent with spectral measurements of QSS XUV lasers reported by different authors in the 1990s, although they were based on slightly different pumping conditions and measurement techniques.