J. Dunn

X-ray laser gain measurements in a collisionally excited germanium plasma

We have used a novel beam-averaging technique that makes use of a segmented wedge array (SWA) to overlap several line foci and to produce a much more uniform linear plasma than has been obtained to date. With this focusing arrangement, laser gain was observed for the first time to our knowledge on a 2s2p63d–2s2p63p, J = 2–1 Ne-like transition at 198.99 A. The experiments were carried out on the LP2 Nd:glass laser system operating at 1.06 μm with incident energies of ~125 J/cm of line focus. We also observed gain on five 3p–3s transitions, using both the SWA and crossed cylindrical lenses to produce the line focus.

Effects of irradiation non-uniformity on X-ray laser physics

Abstract Time resolved monochromatic imaging diagnostic is used to study in lasing plasma the effects of laser irradiation non-uniformity on line focused plasma conditions. Significant large scale non-uniformities are observed with a conventional focusing system. A new focusing arrangement (SWA) is used to produce a more uniform linear plasma. Quantitative measurements of the influence of the local laser intensity variations on the ionization balance and on the recombination time history are presented and discussed.

Energy transport in plasmas produced by a high brightness KrF Raman laser

Abstract A high brightness KrF Raman laser generating 60 GW, 40 ps pre-pulse free pulses has been focused to an 8 μm focal spot at 9x10 16 W cm -2 . Axial and lateral transport of energy has been studied by analysis of X-ray images of the focal spot and from X-ray spectra emitted by a thin layer of aluminium beneath a variable thickness of CH polymer on planar targets. The results show strong lateral transport of energy and reduced axial penetration of heating.

Dynamics of Ne-like populations in the germanium x-ray laser

Time‐ and two‐dimensional (2‐D) space‐resolved monochromatic imaging is used to study the dynamics of Ne‐like populations in the electron collisionally excited germanium x‐ray laser. Large‐scale variations in the n=3 level population, specifically the upper level of the 2s2p63d‐2s2p63p laser transition, are observed in plasmas created in uniform and nonuniform irradiation conditions, and the degree of homogeneity along the amplification axis is related to the x‐ray gain. The influence of inhomogeneities on the core‐excited 3d‐3p x‐ray lasers is discussed.

Observations of x-ray gain in a laser-produced germanium plasma

Slab germanium targets have been irradiated in a line focus geometry with 1-3 nsec FWHM, 1.06-micron laser pulses at irradiances of I equal to or less than 10 exp 13 W/sq cm. The effect of varying the rise-time of the driving laser pulse on the amplification of 3-3 soft X-ray lasing lines is investigated. Results of short-pulse (100 psec FWHM) experiments have also shown gain on the same lasing transitions, but at substantially higher irradiances of I equal to or greater than 3 x 10 exp 13 W/sq cm.

Experiments with SPRITE 12 ps facility

Lateral and axial thermal energy transport in laser-plasma interactions has been studied using a short (12 psec) pre-pulse free KrF pumped Raman laser pulse (λ = 268 nm) of low beam divergence. A new method of producing narrow line foci using random phase plates was employed to study the plasma conditions required to generate high gain, short wavelength recombination X-ray lasers. In addition, the laser energy was focused into a small focal spot (8 μm) for higher intensity (1-2 x 1017 cm-2) interaction studies.

The inhomogeneity issue for X-ray lasers

Summary form only given. Temperature and density homogeneity along X-ray laser line plasmas is important for the optimization of the gain. Irradiation nonuniformities are usually present in experiments and produce large-scale inhomogeneities in the plasma emission along the amplification axis. The authors have investigated the evolution of such inhomogeneities on Ne-like Ge line plasmas and their effect on the gain with a space- and time-resolved monochromatic imaging technique, for both uniform and nonuniform laser irradiation. In particular, they have studied 3d-3p lasing at 199 /spl Aring/ and the quadrupole E2 (8.031 /spl Aring/) and dipole 3A (8.371 /spl Aring/) line emissions originating from its upper and lower states, respectively.

Diagnostics of x-ray laser plasmas (Invited Paper)

Thomson scattering, X-ray diagnostics and optical interferometry are employed to characterize both collisionally excited and recombination X-ray laser plasmas. Spatially and time-resolved Thomson scattering spectra from carbon plasmas provide the electron and ion temperatures, which are compared with hydrodynamic computer modelling. The electron density is inferred from the recorded interferograms. Time-integrated X-ray spectra in the keV range are used to characterize very precisely the optimum irradiance conditions for lasing in Ne-like germanium plasmas. Also, electron temperatures obtained with the 5C/4C line ratio, assuming a PLTE model, are compared to Thomson scattering results.

Laser-plasma energy transport with high-intensity short laser pulses

In order to investigate the production of plasma with simultaneous high density and high degree of ionisation and to study laser-plasma energy transport, experiments have been undertaken to measure the plasma electron densities formed in a thin layer of aluminium buried below an overlay of plastic when the plastic overlay is irradiated by focussed lasers of wavelength (and pulse length).53tm (2Ops) ; .35im (2Ops) and .27 pm (5Ops) . For the .53im and .35pni wavelengths, the shorter pulse length (2Ops) results in higher time-averaged electron densities (up to 6 x 1022 cm3) than for the .27tm wavelength experiments with 50 ps pulse length, but the production of hydrogen-like aluminium relative to helium-like is less with the shorter pulse-length.