Soft x-ray brilliance of femtosecond and picosecond laser-plasmas

Soft x-ray spectra (10-70 Å) from carbon and aluminium plasmas produced by high-intensity laser pulses have been studied as a function of laser pulse duration (130 fs-1.3 ps) and intensity (10¹⁴-5 × 10¹⁷ W cm^-2) for two different laser wavelengths (248 and 800 nm). The x-ray energy emitted from the plasma into specific lines and into the continuum has been measured by means of an absolutely calibrated x-ray spectrograph and thus allows the water window x-ray yield from plasmas produced by long and short wavelength laser radiation to be compared directly. Comparison was made between the dependence of the x-ray energy and width of the x-ray lines on the laser pulse duration, wavelength and intensity. The experimental results have been related to hydrocode simulations.