Influence of chromium plasma characteristics on high-order harmonics generation

We demonstrate the method of laser-induced plasma formation and characterization for achieving efficient high-order harmonics generation during the ablation of chromium and propagation of femtosecond pulses through the optimally adjusted plasma. The dynamics of chromium plasma spreading out from the target surface is correlated with the maximal harmonic yield for the non-resonant harmonics and resonance-enhanced harmonic. Plasma velocities at different regimes of ablation were correlated with the determination of the optimal delay between the heating pulses used for target ablation and femtosecond driving pulses propagating through this plasma. Laser-induced breakdown spectroscopy was used for the optimization of the fluency of heating pulses and determination of the parameters of plasma. The harmonics up to the forty order (in the case of 1300 nm driving pulses) and thirty order (in the case of 800 nm driving pulses) were obtained. The enhancement of the resonance-induced 29th harmonic of 800 nm radiation and 47th harmonic of 1300 nm radiation showed a direct relationship with the optimization of plasma characteristics.