Enhancement of spectral line intensity and lifetime of femtosecond laser-induced Cu plasma in a cylindrical cavity

The spatial confinement effects in the femtosecond laser-induced Cu plasma contained within a cylindrical cavity are studied by optical emission spectroscopy. The Cu atomic emission intensity and spectral line lifetime are enhanced significantly when a cylindrical cavity with an inner diameter of 6 mm confined the femtosecond laser-induced Cu plasma. The enhancement factor of the emission intensity under the spatial confinement depends on the upper level energy of the spectral line, and the maximum enhancement factors is about 2.48 for the Cu I 529.3 nm spectral line. The spatial confinement can effectively prolong the lifetime of the femtosecond-induced Cu and the persistence time of the plasma is near to 7 mu s. The enhancements of the spectral line intensity and lifetime are attributed to the increased electron temperature and density owing to the spatial confinement, and the mechanism for the enhancement effects with the cylindrical cavity are discussed in terms of the shockwave interactions.