P. Jaeglé

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.

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.

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.

Investigation of XUV amplification with Ni-like xenon ions using laser-produced gas puff plasmas

Abstract This paper presents results of a study of a gas-puff plasma soft-X-ray amplifier using Ni-like xenon. The target was created by pulsed injection of xenon from a high-pressure solenoid valve through a nozzle in the form of a 2 cm long slit. The plasma was produced by irradiating the gas puff plume with six line-focused laser beams. The uniformity of the plasma column was monitored using a crossed-slit X-ray pinhole camera while the ionisation balance was assessed with the help of keV resonance spectra obtained by a crystal spectrometer. A modest amplification was seen at two J =0–1 lasing lines allowing however the first precise measurement of their wavelengths. Comparison of the results with a previously reported amplification in the gas-puff system is made, indicating issues essential to the performance of these systems.

The influence of prepulse level on the 3p-3s XUV laser output from Ne-like ions of Zn, Cu and Ni

Abstract We have studied the effect of prepulses in enhancing the efficiency of generating ASE beams in soft X-ray laser plasma amplifiers based on pumping Ne-like ions. Slab targets were irradiated with a weak prepulse followed by a main plasma heating pulse of nanosecond duration. Time-integrated: time and spectrally resolved and time and angularly resolved lasing emissions on the 3p-3s ( J = 0–1) XUV lasing lines of Ne-like Ni, Cu and Zn at wavelengths 232 A, 221 A and 212 A respectively have been monitored. Measurements were made for pre-pulse/main-pulse intensity ratios from 10 −5 –10 −1 and for pump delay times of 2 ns and 4.5 ns. Zinc is shown to exhibit a peak in output intensity at ∼ 2 × 10 −3 pre-pulse fraction for a 4.5 ns pump delay, with a main pulse pump intensity of ∼ 1.3 × 10 13 W cm −2 on a 20 mm target. The Zn lasing emission had a duration of ∼ 240 ps and this was insensitive to prepulse fraction. The J = 0–1 XUV laser output for nickel and copper increased monotonically with prepulse fraction, with copper targets showing least sensitivity to either prepulse level or prepulse to main pulse delay. Under the conditions of the study, the pre-pulse level was observed to have no significant influence on the output intensity of the 3p-3s ( J = 2−1) lines of any of the elements investigated.

Recombination scheme in lithium-like ions for X-UV amplification

Recombination in lithium-like ions in a fast cooling plasma is an alternative attractive approach to the X-ray laser because, at a given lasing wavelength, it requires the lowest pumping energy of the main pumping schemes. In this paper we give a status report on recent experiments concerning the Li-like X-ray laser, and we discuss the problem of lengthening of the active medium necessary to obtain a true X-ray laser.