A COMPUTATIONAL INVESTIGATION OF THE NEON-LIKE GERMANIUM COLLISIONALLY PUMPED LASER

The complex problem of a collisionally pumped Ne-like geranium laser is examined through several detailed models. The central model is EHYBRID; a 1 1/2D fluid code which self consistently treats the plasma expansion with the atomic physics of the Ne-like ion for 124 excited levels through a collisional radiative treatment. The output of EHYBRID is used as data for ray-tracing and saturation codes which generate experimental observables. A detailed description of the models is given.

Measurement of the duration of X-ray lasing pumped by an optical laser pulse of picosecond duration

Measurements of the duration of X-ray lasing pumped with picosecond pulses from the VULCAN optical laser are obtained using a streak camera with 700 fs temporal resolution. Combined with a temporal smearing due to the spectrometer employed, we have measured X-ray laser pulse durations for Ni-like silver at 13.9 nm with a total time resolution of 1.1 ps. For Ni-like silver, the X-ray laser output has a steep rise followed by an approximately exponential temporal decay with measured full-width at half-maximum (FWHM) of 3.7 (+/-0.5) ps. For Ne-like nickel lasing at 23.1 nm, the measured duration of lasing is approximate to10.7 (+/-1) ps (FWHM). An estimate of the duration of the X-ray laser gain has been obtained by temporally resolving spectrally integrated continuum and resonance line emission. For Ni-like silver, this time of emission is approximate to22 (+/-2) ps (FWHM), while for Ne-like nickel we measure approximate to35 (+/-2) ps (FWHM). Assuming that these times of emission correspond to the gain duration, we show that a simple model consistently relates the gain durations to the measured durations of X-ray lasing. (C) 2002 Elsevier Science B.V. All rights reserved.

Spatial coherence of x-ray laser emission from neonlike germanium after prepulse

The time-integrated spatial coherence of neonlike germanium x-ray laser radiation has been studied with a new dispersing coherence diagnostic. Angle-dependent spatial coherence data are recorded by sampling the diverging beam at each lasing wavelength in several directions simultaneously. Measurements of the spatial coherence, and hence effective source sizes, relevant to the output beams from double-slab targets for the J = 2-1 spectral lines at wavelengths 28.6, 23.6, and 23.2 nm and for the J = 0-1 line at 19.6 nm show differences, which indicate different conditions in the plasma volume amplifying these emissions. Targets are pumped by subnanosecond pulse drivers, with and without a prepulse, but 19.6 nm emission is detected only in the prepulsed case. The differences are discussed in terms of the time evolution of the spectral lines. (C) 1997 Optical Society of America.

A time-resolved spectroscopy study of the resonance-line emission in the Ge XXIII XUV laser

A comparison is presented of the temporally resolved resonance-line emission from the Ne-like Ge XUV laser (pumped with nanosecond pulses) with the predictions for the same emission from the hydro-atomic code EHYBRID. The specific lines chosen were the two 3s-2p Ne-like lines at 10.01 and 9.762 Angstrom, and the 3s-2p F-like group of lines in the 9.4-9.6 Angstrom region. Modification of the code to include 112 excited levels of the F-like ion facilitated a direct comparison between experiment and model of (i) the temporal variation of the emissions and (ii) the variation of the peak intensity ratios of the F-like to Ne-like emissions with irradiance on target.

Mapping the evolution of optically generated rotational wave packets in a room-temperature ensemble of D2

A coherent superposition of rotational states in D2 has been excited by nonresonant, ultrafast (12 fs), intense (2×1014 W cm-2) 800 nm laser pulses, leading to impulsive dynamic alignment. Field-free evolution of this rotational wave packet has been mapped to high temporal resolution by a time-delayed pulse, initiating rapid double ionization, which is highly sensitive to the angle of orientation of the molecular axis with respect to the polarization direction, . The detailed fractional revivals of the neutral D2 wave packet as a function of and evolution time have been observed and modeled theoretically.

Developments in X-ray laser pumping with travelling wave at Vulcan

Saturated output has been observed for both Ne and Ni-like X-ray lasers when Pumped in the transient mode. As these 'normal' transitions display very high gain, attempts have been made to observe a 2p --> 2s inner shell transition in Ne-like ions, which scale well towards the water window. Modelling of the pump conditions for Ge lasing at 6.2 run is presented. As the predicted gain is low the experiment was set up for 18 mm targets. Shots were taken on Ti, Fe, Ni and Ge. A similar to1.5 ps travelling wave pulse is applied at various times after the peak of a long, preforming Pulse. Various pump conditions were attempted but no inner shell X-ray laser was detected.