A. Carillon

Soft-x-ray amplification by lithium like ions in recombining hot plasmas

This paper describes calculations and experiments about soft-x-ray amplification by lithiumlike ions in recombining laser-produced plasmas. Time- and space-dependent population inversion densities calculated with a collisional-radiative model used as the postprocessor of a hydrodynamic code are reported. Amplification diagnostic accuracy in plasma experiments is discussed. Time-integrated and time-resolved measurements of gain are presented, especially at 105.7 A in lithiumlike aluminum. It is shown that, in a plasma produced by a 3-nsec laser pulse, the peak of amplified radiation occurs about 7 nsec after the top of the pulse. The maximum gain–length product measured previously was 2–2.5. A short description of a future experiment designed for producing a much larger gain is presented.

Ultraviolet luminescence of CsI and CsCl excited by soft x-ray laser

We present the observation of solid material luminescence excited by soft x-ray laser. The 21.2 nm photons of the soft x-ray laser of the Laboratoire d’Utilisation des Lasers Intenses (Palaiseau, France) have been used to induce ultraviolet luminescence in CsCl and CsI. The laser supplied up to 6×1012 photons in 80 ps. A single laser shot was sufficient to obtain luminescence spectra with very good resolution. In the case of CsI, the use of two illumination conditions, differing by a factor 150 in intensity, showed the collapse of luminescence efficiency for very strong illumination. The quenching effect is discussed in terms of the large increase of crystal excitation mean density, altering the usual process of luminescence centers production.

Amplification of soft-X-ray spontaneous emission in aluminium and magnesium plasmas

Amplification of spontaneous emission at 105.7 and 127.9 AA is reported for Li-like aluminium and magnesium in recombining laser-produced plasmas. Evidence of gain is deduced from the variation of radiation intensity according to the length of a line-shaped plasma. Detailed calculations of rate equations with a suitable plasma model, associated with numerical simulations of plasma hydrodynamics, predict population inversions between 3d and 5f levels, in accordance with these experiments.

Interferograms obtained with a X-ray laser by means of a wavefront division interferometer

Abstract A wavefront division interferometer has been used for the first time with a soft X-ray laser (λ = 21.2 nm). The experiment aims to demonstrate X-ray laser interferometry in this configuration and to investigate the phase shifting measurement accuracy as well. The X-ray laser is generated in a neon-like zinc plasma in which it makes two passes thanks to a multilayer mirror half-cavity. The X-ray pulse duration is ≈50 ps. The beam has a very high brightness (≈4 × 10 15 W cm −2 sr −1 in 0.01% bandwidth) which allows us to place the interferometer far from the source (2.8 m) and thus to benefit by a large transverse coherence width. The interferometer consists of a Fresnel bi-mirror which adds coherently one part of the X-ray laser beam section to the other one. Single laser-shot interferograms of a reflecting sample provided with a λ 2 dephasing step (51.7 nm height) have then been successfully recorded. The phase shifting accuracy resulting from the smallest observable fringe change is about λ 20 .

Soft X-ray amplification in aluminium recombining plasma produced from a thin coated fibre

Thin carbon fibres, coated with aluminium, are irradiated with approximately=120 ps, 0.53 mu m laser pulses yielding a specific absorbed energy of approximately=4 J cm-1 and time-resolved gain measurements on the n=4-3 and n=5-3 transitions of lithium-like Al XI ions in the recombining plasma are made. In particular, gain on the 4f-3d line at 15.4 nm is measured with alpha max approximately=2-3 cm-1 using both single-shot and multi-shot techniques. Gain measurements from multi-shot data on the 5f-3d line at 10.6 nm indicate alpha max approximately=1.5 cm-1. Observations are compared with theoretical calculations, discrepancies are noted and the need for reproducible plasma conditions in low gain-length product data sets is discussed.

Soft–X-Ray Amplification in Recombining Aluminum Plasma

This paper reports time-resolved measurements of gain at 105.7 A in an aluminum plasma produced by a laser. It is shown that the amplification occurs during the plasma cooling, at the end of the laser pulse. The observed time-variation of the gain agrees with the prediction of a plasma recombination model used for calculating the level populations of the lithium-like Al10+ ions.

Transient pumping of a Ni-like Ag x-ray laser with a subpicosecond pump pulse in a traveling-wave irradiation geometry

We report what is to our knowledge the first demonstration of a transient x-ray laser pumped by a 350-fs pulse in a traveling-wave irradiation geometry. For a 500-fs pump pulse the traveling-wave irradiation was found to have a strong effect on enhancing the Ni-like silver 4d–4p lasing emission at 13.9 nm. The signal enhancement was significantly less when the pulse duration was lengthened to 1.7 ps. The experimental observations are well reproduced by a simple model when the duration of gain is taken of the order of 15–20 ps. For the 500-fs pulse a gain coefficient of 14.5 cm-1 was measured for plasma lengths up to 7 mm. Refraction of the amplified photons is believed to be the main cause of the limitation of the effective amplification length.

Beam properties of a deeply saturated, half-cavity zinc soft-x-ray laser

We report what is to our knowledge the first experimental study of beam quality and prepulse effect for a deeply saturated neonlike Zn soft-x-ray laser at 21.2 nm, comparing two distinct regimes of operation: amplified spontaneous emission (in single pass) and double pass. The single-pass x-ray laser output emitted by a 30-mm-long plasma column delivers a smooth, highly symmetric ellipsoidal beam with horizontal and vertical divergence of 3(±0.5) and 5(±0.5) mrad, respectively. With a half-cavity consisting of a Mo:Si flat multilayer mirror, the x-ray laser output is boosted by factor of ∼11, providing a narrowly collimated beam with horizontal and vertical divergence of 3.8(±0.5) and 5.8(±0.5) mrad, respectively. The dependence of the beam parameters on the half-cavity setup and on the level of prepulse is described and discussed.

INVESTIGATION OF STRONG ELECTRIC-FIELD INDUCED SURFACE PHENOMENA BY SOFT X-UV LASER INTERFEROMETRY

Abstract Transient perturbed niobium surface states are observed for the first time during a long continued action of the applied DC-field owing to surface imaging by the means of an X–UV laser interferometry technique.

X-Ray Laser Experiment with a Long Recombining-Plasma Column

We report the results of a soft-X-ray laser experiment in which five Nd-laser beams are used for producing a 6-cm long aluminium plasma column. Population inversion occurs for the 3d-5f transition of lithiumlike ions (λ = 105.7 A) according to the plasma recombination scheme. A double-pass device is achieved with a W/C multilayer mirror. Double-pass is shown to increase largely the intensity and the directivity of the beam at 105.7 A. A plasma produced from thin aluminium target supplies a gain coefficient of 0.5 cm-1, whereas population inversion is strongly reduced by radiation trapping in the case of massive targets.