Producing ultrashort, ultraintense plasma-based soft-x-ray laser pulses by high-harmonic seeding

Simulations show that intense plasma-amplified pulses of 100 fs duration and below are feasible by seeding specifically tailored plasma with an ultrashort pulse of high harmonic radiation. Seeding overcomes gain narrowing by driving amplifying media into saturation earlier, and compensates for reduced gain resulting from boosting the lasing transition linewidth. We conclude that ultrahigh intensities (above ${10}^{16}$ W cm${}^{-2}$) could be reached.

Figure 1

FWHM determined experimentally by Koch et al. [10] and our predictions as a function of distance into the plasma amplifier with 36 mÅ of Doppler broadening and a 23.5 mÅ Lorentzian component, as calculated in this work (solid line). An unrealistic Lorentzian value of 1 mÅ (dashed line) was also used to illustrate saturation rebroadening, though these predictions take no account of collisional redistribution (see main text).

Figure 2

Predicted FWHM of a 20.6 nm laser pulse versus distance into an Ne-like Se plasma under differing plasma conditions. The unbroken lines show predictions under the original Koch conditions (see text) and the broken lines show those under the revised conditions (again, see text). In each case, the seeding level is given in terms of the respective saturation intensity, $I_s$.

Figure 3

Peak intensities corresponding to Fig. 2 (same legend).

Figure 4

Top: Pulse shape as it passes through the plasma amplifier under the revised conditions with a seeding level of $0.01I_s$ (see main text). Bottom: As above but with an expanded horizontal scale.

Figure 5

Plots of predicted electron density and temperature as a function of the distance from the longitudinal plane of an Se foil of 0.15 $\mu \mathrm{m}$ initial thickness at 400 ps after the peak intensity of double-sided irradiation by long wavelength pulses of 250 ps FWHM and $~2\times {10}^{13}$ W cm${}^{-2}$ intensity. The simulation was performed using the ehybrid 1.5 D atomic physics and hydrodynamic fluid code [27].