Demonstration of the 101st harmonic generated from a laser-produced manganese plasma

Abstract

We demonstrate the generation of the 101st harmonic (wavelength $\ensuremath{\lambda}=7.9\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$) from manganese plasma, which is generated using the plasma high-order harmonic technique. We also investigate the variation of the high-order harmonic distribution from the manganese plasma plume as a function of the prepulse and main pulse intensities. The harmonic cutoff was at the 31st order, for pump intensities below the barrier suppression intensity for singly charged Mn ions. However, by using higher prepulse and main pulse intensities, the harmonic cutoff was extended to the 101st order, with an appearance of second plateau for harmonics higher than the 31st order. In this case, the low-order harmonics decreased in intensity, or completely disappeared, and the spectrum for wavelengths longer than $27.6\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ was dominated by plasma line emission. The origin of the harmonics appearing at this short wavelength plateau is attributed to the interaction of the intense main pump laser field with doubly charged manganese ions.