Using the grazing incidence pumping technique with a 600 mJ, 500 ps background pulse and a 250 mJ, 200 fs main
pulse the lasing emission from a molybdenum target has been studied. A flat field spectrometer designed to observe the
X-ray laser emission in both the first and second orders was used to record the time integrated data. Time resolved data
was obtained by installing an Axis-Photonique PX1 X-ray streak camera to observe the first order output from the
spectrometer whilst retaining the time integrated second order observation. In this paper both time integrated and time
resolved data are presented for a range of grazing angles, target lengths, delays between pumping pulses and pumping
energy. Comparisons are also drawn with simulations from the Ehybrid and Medusa codes. An additional experiment is
also described in which a two colour pumping method is used to investigate lasing at short wavelength from high Z
targets (Z ≥ 62).
We present a review of recent development and applications of soft x-ray lasers, undertaken at the PALS Centre. The applications benefit from up to 10-mJ pulses at the wavelength of 21.2 nm. We describe the pumping regimes used to produce this soft x-ray laser, and outline its emission characteristics. A significant fraction of applications carried out using this device includes probing of dense plasmas produced by IR laser pulses and high-energy-density-in-matter experiments. Results obtained in these experiments are reviewed, including x-ray laser probing of dense plasmas, measurements of transmission of focused soft x-ray radiation at intensities of up to 10<sup>12</sup> Wcm<sup>-2</sup>, measurements of IR laser ablation rates of thin foils, and probing high density plasmas by x-ray laser Thomson scattering
The rate of laser ablation at irradiances of ~2x10<sup>14</sup> Wcm<sup>-2</sup> of solid iron and aluminum has been measured using the
transmission of a neon-like zinc X-ray laser at 21.2 nm through thin iron and aluminum targets. It is shown that the
opacity of ablated material falls rapidly with increasing temperatures and decreasing density from the solid value. As
ablated plasma becomes transparent to the X-ray laser flux, the thickness of solid, unablated material and hence the rate
of ablation can be measured from time resolved X-ray laser transmission. A self-regulating model of laser ablation and
fluid code simulations with absorption to thermal plasma of 5-10% show agreement with our measured ablation rates.
The Axis-Photonique PX1 fast X-ray streak camera records the temporal structure of events with picosecond accuracy.
Using a potassium iodide photocathode the streak camera has been characterised for the effects of space charge. In a
recent grazing incidence pumping X-ray laser experiment the streak camera was coupled to the output of a flat field
spectrometer to observe first order diffraction. The second order was observed using a CCD camera. In this paper data
is presented from this experiment comparing the brightness of the X-ray laser emission with the dispersion of the
streaked image both temporally and spectrally (non temporal direction). Consequently measurements of the dynamic
range of the streak camera are made. The results are compared with data from previous experiments.
Experimental measurements of the opacity of plasmas at densities close to solid state and temperatures ~ 60 - 300 eV using a probing X-ray laser are presented. Utilizing thin targets, opacities of iron have been measured using x-ray lasers of photon energy 89 eV created by pumping with the VULCAN RAL laser. The thin targets are separately heated by spot focus laser pulses. We have demonstrated that X-ray laser brightness is sufficient to overcome the self-emission of hot plasma so that useful opacity measurements can be made. Due to their high brightness, x-ray lasers can fulfill a useful niche in measuring opacity and other phenomena associated with laser-plasma interactions. Quantities such as opacity measured in laser-plasmas are useful elsewhere. For example, plasma opacity is important in understanding radiative transfer in the sun.
We present a detailed analysis of an experiment carried out recently in which the temporal coherence of the Ni-like silver transient X-laser at 13.9 nm was measured. Two main consequences of this measurement will be discussed and interpreted with numerical calculations. First we show that the high temporal coherence length measured corresponds to an extremely narrow spectral width of the X-ray laser line. Second we show that the high temporal coherence helps to explain the presence of small-scale structures observed in the cross-section of all transient X-ray laser beams.
We give an overview of recent advances in development and applications of deeply saturated Ne like zinc soft X-ray laser at PALS, providing strongly saturated emission at 21.2 nm. Population inversion is produced in the regime of long scale-length density plasma, which is achieved by a very large time separation between the prepulse (<10 J) and the main pump pulse (~500 J), of up to 50 ns. This pumping regime is unique in the context of current x-ray laser research. An extremely bright and narrowly collimated double-pass x-ray laser beam is obtained, providing ~10 mJ pulses and ~100 MW of peak power, which is the most powerful soft X-ray laser yet demonstrated. The programme of applications recently undertaken includes precision measurements of the soft X-ray opacity of laser irradiated metals relevant to stellar astrophysics, soft X-ray interferometric probing of optical materials for laser damage studies, soft X-ray material ablation relevant to microfabrication technologies, and pilot radiobiology studies of DNA damage in the soft X-ray region. A concomitant topic is focusing the x-ray laser beam down to a narrow spot, with the final goal of achieving ~10<sup>13</sup> Wcm<sup>-2</sup>.
The ablation of plain aluminium foil and aluminium foil with a thin (50 nm) iron coating was observed using a neon-like zinc x-ray laser. The 21.2 nm x-ray laser was produced by a double pass of a 3 cm long zinc target at the PALS centre in Prague. The x-ray laser was used to probe the sample targets as they were heated by a separate laser beam of 10 J, focussed to a 100 micron diameter spot. The data from the experiment are presented and compared with Ehybrid simulations and simple ablation rate calculations.
We review our recent progress in the development of transient x-ray lasers and of their application to plasma diagnostic. The first observation of C-ray laser emission at the new PHELIX-GSI facility is reported. This TCE X-ray laser will be a promising tool for heavy-ion spectroscopy. We then present the main results obtained at the LULU-CPA facility with a compact high-resolution X-UV imaging device. This device was used to investigate the spatial source structure of the Ni-like silver transient X-ray laser under different pumping conditions. The key-role of the width of the background laser pulse on the shape of the emitting aperture is demonstrated. Finally the imaging device was used as an interference microscope for interferometry probing of a laser-produced plasma. We describe this experiment performed at APRC-JAERI.
Below saturation, X-ray laser output shows a reduction in pulse duration and frequency bandwidth as the gain-length product increases. Above saturation, both quantities can be expected to rebroaden. The duration of gain can be close to an order-of-magnitude longer than the output pulse duration. With gain-length products just below saturation, X-ray lasing at 13.9 nm in nickel-like silver has been measured with a pulse duration Δ<i>t</i> of 3 - 4 ps and an estimated frequency bandwidth Δ<i>v</i> of 5×10<sup>11</sup> Hz. Such values imply that the pulses are close to transform limited with Δ<i>t</i> Δ<i>v</i> ≈ 1.5. Measurements of x-ray laser pulse-lengths and gain duration will described in this paper.