XUV Emissions from Terawatt Femtosecond Laser Produced Plasma Columns in Gases

摘要

Terawatt femtosecond laser pulses were focused into aa gas cell to produce plasma columns in gases of N_2, O_2, and He. The axial xuv emission spectra that were generated are reported and analyzed. The xuv amplifications on transitions of NIII 3s(~2S)-2p(~2P) at 45.2 nm and OIII 2p3s(~3P)-2p~2(~3P) at 37.4 nm in low-charged nitrogen and oxygen ions were successfully demonstrated by a linearly-polarized 100-fs pump laser pulse of only 25 mJ. Strong axial xuv emission lines from a laser-produced plasma column in helium gas were also observed, however, no amplification was observed for the L_ alpha line at 30.3 nm. High-order harmonics from a helium plasma column were also investigated with different pump energies under the defocusing condition for the laser beam.