Short pulse pumped X-ray lasers

Double laser pulses of duration similar to 75 ps and short laser pulses similar to 1 ps superimposed on longer duration background pulses have been shown to efficiently pump lasing in Ne-like and Ni-like ions. For the 75 ps pumping, X-ray laser output without travelling wave pumping is shown to be well-described by a model of ASE output. With I ps pumping, the X-ray laser output with different velocity travelling wave pumping is well-fitted with an extension to the ASE model allowing for travelling wave excitation of the gain along the plasma line. The model is used to investigate the production of short (<1 ps) x-ray laser pulses and the effects of non-ideal travelling wave velocities on the X-ray laser output. Resonance line spectra of emission perpendicular to the plasma line are measured and simulated. It is shown that an accurate opacity model for the more intense Ne-like ions is needed to correctly simulate the spectra.

COLLISION PUMPED SOFT-X-RAY LASERS - PROGRESS AT RAL

Recent developments and progress on collision pumped soft X-ray lasers using the VULCAN glass laser at Rutherford-Appleton Laboratory are presented. This includes saturated output operation of a double target germanium system within a low Fresnel number half-cavity, measurement of the spatial coherence of the output beam in the above and other geometries, use of the beam to demonstrate almost-equal-to 0.15 mum spatial resolution in a full-field microscope and initial studies of other Ne-like and Ni-like systems. Future directions, in the light of new developments of VULCAN facilities, are outlined.

Transient inversion soft X-ray lasers

The collisionally excited transient inversion scheme is shown to produce exceptionally high gain coefficients and gain-length products. Data are presented for the Ne-Like titanium and germanium and Ni-like silver X-ray lasers (XRL's) pumped using a combination of nanosecond and picosecond duration laser pulses. This method leads to a dramatic reduction of the required pump energy and makes down-sizing of XRL's possible, an important prerequisite if they are to become commonly used tools in the Long-term.

Enhancement of optically thick to thin line intensities in solar and stellar coronal plasmas through radiative transfer effects: an angularly resolved study.

An analysis of radiative transfer effects present in the Fe XV ion stage of solar and stellar coronal plasmas provides a general explanation of line radiation intensity enhancement above the optically thin limit. Full linearization radiation transfer is compared with the escape factor method and found to be in good agreement at the lower column densities. An angular study of the enhancement shows that symmetry factors are of great importance. This gives a possible reason for the indeterminate status of opacity in relation to coronal lines of distant stellar sources, where only emission integrated across the whole surface is detected.

An analytic geometry-variant approach to line ratio enhancement above the optically thin limit

We describe a simple theoretical model to investigate the anomalous effects of opacity on spectral line ratios, as previously studied in elements such as Fe XV and Fe XVII. The model developed is general: it is not specific to a particular atomic system, thus giving applicability to a number of coronal and chromospheric plasmas; furthermore, it may be applied to a variety of astrophysically relevant geometries. The analysis is underpinned by geometrical arguments, and we outline a technique for it to be used as a tool for the explicit diagnosis of plasma geometry in distant astrophysical objects.