RESONANT HIGH-ORDER HARMONIC GENERATION OF PICOSECOND ND:YAG LASER RADIATION IN LEAD PLASMA

The advantages of high-order harmonic generation (HHG) of laser radiation in a plasma plume could largely be realized with the use of low-excited and weakly ionized plasma, because the limiting processes governing the dynamics of the laser frequency conversion would play a minor role in this case. This has been confirmed by several studies concerned with high-order harmonic generation in the plasma plumes. A substantial increase in the cutoff of the generated harmonics, the emergence of a second plateau in the intensity distribution of highest order harmonics, the high efficiencies obtained with several plasma plumes, the resonance enhancement of individual harmonics, the efficient harmonic enhancement in the plasma plumes containing clusters of different materials and other properties have demonstrated the advantages of the application of specially prepared plasmas for the HHG. In this connection, a search for new plasma media and definition of the best experimental conditions, such as pulse duration of driving laser field, for efficient HHG in different spectral ranges is a way for further enhancement of harmonic yield. Some metal plasmas, such as indium and tin [1,2] have proven that, at appropriate experimental conditions, they can be considered as excellent plasma media for the enhanced harmonic generation in the 80 – 40 nm spectral range using ultrashort laser pulses. Moreover, some harmonic orders (13th harmonic from In plasma and 17th harmonic from Sn plasma in the case of 800 nm, femtosecond radiation) demonstrated the enhancement attributed to the influence of the ionic transitions.