Improvement of high-order harmonics from silver plasma plumes induced by femtoseconds laser pulses

Abstract

Silver plasma plume is one of the potential sources for high-order harmonics generation (HHG) using a driving pulse of 800 nm (Ti: S laser system). The harmonic intensity (yield) and cut-off are significantly affected by ablating laser pulse duration. This work extended the harmonics generation using silver [bulk and nanoparticles (100 nm and 20 nm)] plasma plumes ablated by fs laser pulses. The shorter pulse duration of fs pulses leads to enhanced ions' density, which improves the harmonics' intensity and cut-off (65H). Moreover, the experimental harmonic cut-off for Ag+ is precisely matched with the theoretical cut-off. In Ag2+ ions, the experimental cut-off is ∼1.3 times less than the theoretical cut-off. In addition, we have measured the harmonic spectra of samples using negatively and positively chirped 135 fs driving pulses and compared them with chirp-free 35 fs driving pulse harmonic spectra. The negative and positive chirps of the pulses lead to blueshift and redshift of the harmonic's spectra, with an increase of intensity of low (9H–15H) and higher (17H–41H) range harmonics, respectively. However, the comparison between bulk and nanoparticles (NPs) studies proved that the smallest NPs possess larger HHG efficiency. The present study highlights the selection of short pulse duration, i.e., fs pulses as driving and ablating laser pulses, for enhancing the yield and cut-off of harmonics for next-generation table-top XUV light sources.