A. Klisnick

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.

Pulse-front control of 15-TW pulses with a tilted compressor, and application to the subpicosecond traveling-wave pumping of a soft-x-ray laser

We have implemented an adjustable traveling-wave method of excitation for the transverse pumping of laser media based on tilting one of the gratings of the compressor of a chirped pulse amplification [Opt. Commun.56, 219 (1985)] (CPA) laser chain. We show that the only requirement to obtain the best locally compressed pulse is to slightly tilt and translate one of the gratings from its original position. Exact and approximate expressions of these two motions are derived, allowing an easy reconfiguration of any CPA laser. An experimental validation is performed with the first observation of a unidirectional soft-x-ray lasing when subpicosecond pumping pulses are used.

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.

Optimization toward a high-average-brightness soft-x-ray laser pumped at grazing incidence

We report the near-field imaging characterization of a 10 Hz Ni-like 18.9 nm molybdenum soft-x-ray laser pumped in a grazing incidence pumping (GRIP) geometry with a table-top laser driver. We investigate the effect of varying the GRIP angle on the spatial behavior of the soft-x-ray laser source. After multiparameter optimization, we were able to find conditions to generate routinely a high-repetition-rate soft-x-ray laser with an energy level of up to 3 microJ/pulse and to 6x10(17) photons/s/mm2/mrad2/(0.1% bandwidth) average brightness and 1x10(28) photons/s/mm2/mrad2/(0.1% bandwidth) peak brightness.

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 .

Effective rates for li-like ions; calculated XUV gains in Al10+

This work concerns the modelling of the Li-like recombination X-ray laser. We have improved the description of the ionization dynamics and the gain production in a recombining laser-produced plasma. The contribution of the Li-like excited levels (up to n=30), which are assumed to follow a quasi-steady state evolution with respect to the ionic populations, is now incorporated in the ionization and recombination rates connecting He-like and Li-like ionic species. Simple expressions for these effective rates are derived. The number of Li-like excited levels to be included in the model, as well as the determination of the lower limit of the thermal band are examined. Predicted 3d-4f gain values (3 cm−1 at λ=154.6 Å) when simulating fibre targets cylindrically illuminated by a short laser pulse are now in good agreement with experiments. Persistent discrepancies in other cases (3d-5f inversion or slab targets) are discussed.

Optimization of the non-normal incidence, transient pumped plasma X-ray laser for laser spectroscopy and plasma diagnostics at the facility for antiproton and ion research (FAIR)

Intense and stable laser operation with Ni-like Zr and Ag was demonstrated at pump energies between 2 J and 5 J energy from the PHELIX pre-amplifier section. A novel single mirror focusing scheme for the TCE x-ray laser ~XRL! has been successfully implemented by the LIXAM0MBI0GSI collaboration under different pump geometries. This shows potential for an extension to shorter XRL wavelength. Generation of high quality XRL beams for XRL spectroscopy of highly charged ions is an important issue within the scientific program of PHELIX. Long range perspective is the study of nuclear properties of radioactive isotopes within the FAIR project.

Observation of intense soft-x-ray lasing at the J = 0 to J = 1 transition in neonlike zinc

We present experimental results from recent studies of soft-x-ray lasing in Ne-like Zn (Z = 30). The lasing plasma was produced by irradiation of slab targets as much as 2 cm long with intensities of ~1.4 × 1013 W cm−2 at λ = 1.06 μm in pulses of 600 ps (FWHM). Amplification at three 3p–3s transitions was observed. While the J = 2 to J = 1 transitions at 262 and 267 A provided gain coefficients of 2.3 and 2.6 cm−1, respectively, the J = 0 to J = 1 transition at 212 A exhibited a significantly larger gain of 4.9 cm−1 and yielded a much brighter signal. Furthermore, its temporal characteristics were revealed to be unlike those of the J = 2 to J = 1 transitions. The results indicate that the J = 0 to J = 1 line originates from a different plasma region than do the J = 2 to J = 1 lines and that the temporal evolution of the pumping process into its upper lasing level J = 0 differs considerably from that to the J = 2 levels. In addition, the gain and the gain–length product of ~10 achieved in this experiment are, to our knowledge, the highest ever reported for a driving laser of similar energy (~450 J).

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.