Frequency conversion of femtosecond radiation in magnesium plasma

The generation of high harmonics (up to the 23rd order, λ = 34.6 nm) of Ti:sapphire laser radiation in the prepulse-produced magnesium plasma is studied. The steady decrease of conversion efficiency for each next harmonic order is observed, unlike the plateau pattern registered in the case of boron plume. The main contribution on the limitation of conversion efficiency was caused by the self-defocusing of femtosecond beam. The analysis of spatial and spectral characteristics of high-order harmonics is presented. The conversion efficiency of 17th harmonic generated in magnesium plasma was measured to be 4 × 10−7.