Abstract
Application of high pulse repetition rate lasers opens the way for increasing the average flux of the high-order harmonics generating in the ions- and nanoparticles-containing plasmas ablated on the surfaces of various metal targets. We demonstrate the harmonic generation of 37 fs, 150 kHz, 1030 nm, 0.5 mJ pulses in different plasmas. The formation of plasma plumes on the surfaces of carbon, titanium, boron, zinc, and manganese targets was performed during laser ablation, using 250 fs pulses from the same laser. The ablation of the mixed powder of boron nanoparticles and silver microparticles was used for generation of harmonics with high yield. Harmonics up to the fortieth orders from the carbon plasma were obtained. The estimated conversion efficiencies in laser-produced plasmas were ≤10−5. The photon flux for a single harmonic generating in carbon plasma was estimated to be 8 × 1013 photons/s.
Highlights
High pulse repetition coherent extreme ultraviolet (XUV) sources are required in different areas, such as the recovery of molecular frame photoelectron distribution from the time-of-flight imaging [1], coincidence measurements where more than one detected particle needs to be linked to the same ionization event, such as in cold target recoil ion momentum spectroscopy and reaction microscopy [2,3,4,5], experiments on correlated two-electron emission from solids [6], etc
Independently to the method of rotating target formation, the principle of rotation during ablation becomes crucial for maintaining the proper conditions of harmonics generation in the plasma plumes formed at a high pulse repetition rate
The corresponding fluxes obtained from other laser-produced plasmas (LPPs) were 4 × 1013 (B NP + Ag MP), 2 × 1013 (Mn, B, and Ti) and 1.5 × 1013 (Zn)
Summary
High pulse repetition coherent extreme ultraviolet (XUV) sources are required in different areas, such as the recovery of molecular frame photoelectron distribution from the time-of-flight imaging [1], coincidence measurements where more than one detected particle needs to be linked to the same ionization event, such as in cold target recoil ion momentum spectroscopy and reaction microscopy [2,3,4,5], experiments on correlated two-electron emission from solids [6], etc. HHG at different pulse repetition rates was reported in the case of gas media [7,8,9,10,11]. When using gas jets, the conversion efficiency does not exceed 10−6. Another option is the HHG in plasma. Most of the harmonic generation studies in laser-produced plasmas (LPPs) have been carried out on static targets. The application of ablated plasma using 1 kHz class lasers causes a considerable change in the surface properties of a static target, resulting in the deterioration of the plasma conditions and harmonic generation. Even at a relatively low pulse repetition rate the stability of harmonics decreases after a few hundred shots on the same place of the surface. One can assume that movement of the plasma along the target surface or application of the rotating target can improve the stability of the harmonic yield
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