Comparison studies of high-order harmonic generation in argon gas and different laser-produced plasmas

The gases and laser-produced plasmas (LPP) are both suitable transparent media for high-order harmonic generation (HHG) in the extreme ultraviolet range from near infrared femtosecond laser pulses. In this work, we perform a comparison study of these media as the emitters of harmonics. We demonstrated stronger HHG from different plasmas (Ag, Ag2S, stainless steel) than the harmonics generated from argon gas, especially in the 20–50 nm wavelength range. Different schemes of HHG (single- and two-color pumps, tunable positions of LPP with regard to gas jet) are analyzed, which allowed us to determine the best configurations of separated LPP + gas and gas + LPP schemes for harmonic generation. A three- to twenty-fold increase of harmonic yields are found from LPP compared to the gas medium under similar experimental conditions.

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