Coherent soft-x-ray generation by the harmonics of an ultrahigh-power KrF laser

Abstract

Harmonic generation is investigated at an intensity range of ${10}^{15}$–${10}^{18}$ W/${\mathrm{cm}}^2$ by using a 280-fsec KrF laser. The highest-order harmonic observed with Ne as a nonlinear medium is the 25th (9.9 nm), which gives the shortest-wavelength coherent radiation ever obtained. The inversions or anomalous peaks of harmonic intensity are first found at the 19–21st in Ne, the 17–19th in He, and the 11–13th in Ar. The intensity dependence of the harmonics is measured over a range of ${10}^{15}$–${10}^{18}$ W/${\mathrm{cm}}^2$. The observed distribution of harmonics is discussed and compared with the previous reports.