X-ray laser research at the LULI (Palaiseau)

The X-ray laser program at Palaiseau is based on the recombination scheme in lithiumlike ions, which requires a moderate pump power and seems to be promising for the purpose of scaling to shorter wavelengths. In aluminum plasmas, peak gain values of 2-2.5 cm^-1 have been obtained at a wavelength of 105.7 Å corresponding to the 3d -5f transition, 6 ns after the top of a 2 ns laser pulse. The same transition in sulfur is emitted at 65.2 Å and has shown a gain of 1 cm^-1 in a preliminary time-integrated experiment. Simulations using a collisional-radiative model as the postprocessor of a hydrodynamic numerical code predict amplifications for the 3d-4f, 3d-5f, and 4d-5f transitions. A new experiment, in progress at the present time, has been designed to enhance the gain-length product up to 10-15 at 105.7 Å. The recently extended facilities of the LULI make it possible to produce a 6-cm-long plasma column, keeping the flux density at the same level as in the previous experiments     

New identifications in the Al IV spectrum

Three lines observed in an aluminium laser produced plasma spectrum are added to Soderquist's identifications of Al³⁺ion2p⁶ - 2p⁵nd transitions. Theoretical results, leading to the exchange of previous identifications relative to 2p⁵nd¹P°1 and ³D°₁, are presented.     

Spectral Decomposition of Intracellular Complex Fluorescent Signals Using Multiwavelength Phase Modulation Lifetime Determination

Lifetime-based spectral decomposition using a frequency-domain phase/modulation technique has been developed on our UV confocal microspectrofluorimeter prototype. Examples of such an application are first given in the case of complex mixtures of three overlapping fluorescent components in solution. Preliminary results concerning cellular potential application are also reported in the case of Snarf-1 pH sensor. Limits and perspectives of such an approach at the subcellular level are discussed in view of future improvement.     

Sur le calcul des intégrales R k(n alanblb,nclcndld) de Slater à l'aide des fonctions d'onde hydrogénoïdes

Sans résumé     

A matrix study of the transfer of polarized radiation in plasmas. Application to neon-like germanium lasers

In order to solve the radiative-transfer equation for polarized beams propagating in plasmas a matrix approach is applied. The solution is the four-components Stokes vector, and the effect of the medium on the state of the radiation is represented by an amplification operator. Our approach is applied to the neon-like germanium 23.6 nm line, when a right-circularly polarized beam is injected into an amplifying plasma. The conditions governing the recovery of the initial polarization state are investigated over the entire spectrum of the output. Received: 10 October 1997 / Revised: 12 January 1998 / Accepted: 27 January 1998     

Lasing near 200 Å with neon-like zinc and lithium-like sulfur

In this paper we present the recent results obtained on X-ray lasers with the new facility of LULI (Palaiseau, France). As regards the study of collisional-excitation pumping we show that the J=0–1 line of neon-like zinc, at 212 Å, exhibits a surprisingly large gain coefficient of 4.9 cm^–1. A detailed comparison of the time-dependent intensities of the J=0–1 and the J=2–1 line at 267 Å leads to the conclusion that these two lines are not emitted in the same region of the plasma. On the other hand we performed a theoretical and experimental study of 5g-4f lasing line of lithium-like sulphur at 206.5 Å. For the first time, in the case of plasma recombination pumping, we did not observe any reduction of the gain coefficient when the plasma length is raised from 1 cm to 2 cm. From numerical simulation this is likely due to radiation trapping and similar processes having much less influence on 5g-4f population inversion than on previously observed lithium-like lasing transitions. These results show that large gain-length values should be obtained with 0.5 kJ driving laser pulses.     

SUBCELLULAR DISTRIBUTION OF HYPERICIN IN HUMAN CANCER CELLS

Confocal laser microspectrofluorometric measurements on human T47D mammary tumor cells have been performed to assess the intracellular distribution of hypericin within the various cell compartments: cytoplasmic membrane, cytoplasm and nucleus. Confocal fluorescence measurements obtained from microvolumes (? 1 μm³) located within the three sites of interest show that, while being primarily located in the cell membrane and cytoplasm after a short-term incubation in a 10^?6M hypericin-containing culture medium, hypericin actually reaches the inside of the cell nucleus after a long-term incubation (210 min). Moreover, owing to the relative fluorescence quantum yields of hypericin determined in vitro when the molecule interacts with DNA, membrane and protein model systems, it is assumed that there is a significant accumulation of the drug into the cell nucleus. Consequently, the nucleus has to be considered as a possible target for the toxic action of hypericin.     

High level of low-density lipoprotein receptors enhance hypericin uptake by U-87 MG cells in the presence of LDL

The dependence of the uptake of hypericin (Hyp) by human glioma U-87 MG cells on the level of expression of low-density lipoprotein (LDL) receptors has been studied in this work. A special role of the LDL receptor-pathway for Hyp delivery to U-87 MG cells in the presence of LDL was revealed by the substantial increase of Hyp uptake in the situation, when the number of LDL receptors on the cell surface was elevated. Moreover, the colocalization experiments showed the lysosomal localization of Hyp following the uptake and that the concentration of Hyp in these organelles was enhanced in the cells with elevated number of LDL receptors when the incubation medium contained LDL. Both these findings suggest that LDL and LDL receptor-pathway play an important role in the delivery and accumulation of Hyp into the cells.