Impact of the pulse contrast ratio on molybdenum Kα generation by ultrahigh intensity femtosecond laser solid interaction.

We present an extended experimental study of the absolute yield of Kα x-ray source (17.48 keV) produced by interaction of an ultrahigh intensity femtosecond laser with solid Mo target for temporal contrast ratios in the range of 1.7 × 107-3.3 × 109 and on three decades of intensity 1016-1019 W/cm². We demonstrate that for intensity I ≥ 2 × 1018 W/cm² Kα x-ray emission is independent of the value of contrast ratio. In addition, no saturation of the Kα photon number is measured and a value of ~2 × 1010 photons/sr/s is obtained at 10 Hz and I ~1019 W/cm². Furthermore, Kα energy conversion efficiency reaches the same high plateau equal to ~2 × 10-4 at I = 1019 W/cm² for all the studied contrast ratios. This original result suggests that relativistic J × B heating becomes dominant in these operating conditions which is supposed to be insensitive to the electron density gradient scale length L/λ. Finally, an additional experimental study performed by changing the angle of incidence of the laser beam onto the solid target highlights a clear signature of the interplay between collisionless absorption mechanisms depending on the contrast ratio and intensity.

Monitoring photonic nanojets from microsphere arrays by femtosecond laser ablation of thin films.

By comparing finite-difference time-domain near field simulations and femtosecond laser ablation of thin films, we characterize in three dimensional-space photonic nanojets from microsphere arrays. We demonstrate periodic drilling of transparent films with thickness up to 100 nm (onto absorbing substrates) is feasible with 1-microm diameter silica spheres. Working with larger polystyrene spheres, the apparent increase of the propagation length of the photonic nanojets makes possible to drill films as thick as 500 nm. Interestingly, the lateral width of the produced craters can be maintained below 400 nm evidencing the low divergence of the nanojets. For backside illumination of the arrays, the ablation features are located at the top of the microspheres. We reveal field enhancements in and out the spheres as well as laser energy confinement at the particle substrate interface. The wide variety of features observed in the experiments open routes to fabricating nanomaterials.

Preoperative intraarterial thrombolysis before surgical revascularization for popliteal artery aneurysm with acute ischemia.

Because a popliteal artery aneurysm (PAA) generates emboli that progressively deteriorate the distal arterial network, they can constitute limb-threatening lesions. In 20 to 40% of cases, discovery of PAA coincides with sudden occlusion and resulting acute ischemia. In 40 to 60% of these patients, surgical revascularization fails and amputation is required. The objective of this prospective study was to assess the value of intraarterial thrombolysis to restore distal runoff before surgical revascularization. Between January 1, 1992 and December 31, 1996, we treated 15 PAA causing acute ischemia in 15 male patients with a mean age of 66.7 years (range, 44 to 87 years). Diagnosis was documented by clinical examination and ultrasound imaging. Intraarterial thrombolysis was performed under arteriographic control through a multiperforated catheter inserted by the anterograde femoral route to the thrombus. After an initial bolus of 100,000 U of urokinase, 600,000 to 1,600,000 U was continuously infused over a period of 6 to 18 hr. Heparin sodium was administered throughout thrombolysis. Surgical revascularization was performed within 1 to 4 days (mean, 2 days) after thrombolysis by exclusion and bypass in 14 cases and percutaneous transluminal angioplasty with stenting in 1 case. The ensuing results showed that, if performed carefully, intraarterial thrombolysis can safely prepare patients presenting with occluded PAA with acute ischemia for surgical revascularization to restore distal runoff. We use this combined technique routinely in our department. Morbidity is low in comparison with the risks of amputation.

[Comparison between iopamidol and ioxaglate in digital arteriography of the lower limbs]. / Comparison du iopamidol et du ioxaglate en artériographie numérisée des membres inférieurs.

This prospective study concerning 100 subtraction angiographies of the lower limbs compared two iodine concentrations of iopamidol (300 and 370 mg l/l) and ioxaglate (320 and 350 mg l/l). More pain and movements disturbed the subtraction with iopamidol 370 in comparison with ionic contrast media (p < 0.005). The quality of the contrast was better with ioxaglate 350 (p = 0.05) than with the others. This one appears to be a good compromise for this type of examination.