Effects of ambient air pressure on surface structures produced by ultrashort laser pulse irradiation.

We report an experimental analysis addressing striking effects of residual air ambient pressure, from atmospheric conditions (103 mbar) to high vacuum (10-4 mbar), on the surface structures induced on a silicon target by direct femtosecond laser irradiation. We observe an interesting direct impact of the ambient pressure on the period and depth of the generated ripples as well as on the formation of microgrooves. Moreover, a significant correlation is observed between the ripples' period and depth. The change of pressure is accompanied by a variation of the degree of nanoparticle coverage, which is eventually recognized as an important factor for the development of the final surface structures. These results shed light on the intriguing mechanisms underlying the formation of the various surface textures, also evidencing that the ambient pressure can act as an effective parameter to tailor some characteristic features of the processed surface.

Laser ablation of silicon induced by a femtosecond optical vortex beam.

We investigate laser ablation of crystalline silicon induced by a femtosecond optical vortex beam, addressing how beam properties can be obtained by analyzing the ablation crater. The morphology of the surface structures formed in the annular crater surface allows direct visualization of the beam polarization, while analysis of the crater size provides beam spot parameters. We also determine the diverse threshold fluences for the formation of various complex microstructures generated within the annular laser spot on the silicon sample. Our analysis indicates an incubation behavior of the threshold fluence as a function of the number of laser pulses, independent of the optical vortex polarization, in weak focusing conditions.

Stepwise behaviour of magnetization temperature dependence in iron nanoparticle assembled films.

An unusual stepwise behaviour is reported in the temperature dependence of the zero field cooled magnetization in iron nanoparticle dense films produced by ultra-short pulsed laser deposition assisted by irradiation of nanoparticles with a nanosecond UV laser pulse, appropriately delayed, during their flight from the target to the substrate. This behaviour, induced by the particle system's morphology, characterized by clusters of tightly coupled nanoparticles as well as by some voids between them, is ascribed to the competition between Zeeman energy density, intracluster anisotropy energy density and intercluster exchange energy density. A phenomenological model and Monte Carlo simulations are reported, which support the proposed interpretation.

Magnetic behavior of Ni nanoparticle films produced by two laser irradiations in vacuum.

Ni Nanoparticle assembled thin films were prepared using an unconventional approach based on the use of a secondary nanosecond (ns) ultraviolet (UV) laser irradiation interacting with the plume of ablated nanoparticles (NPs) during the femtosecond pulsed laser deposition (fs-PLD). The secondary laser beam determines the reduction of the NPs size and their dispersion by partial vaporization of the NPs during their flight from the target to the substrate. The proper selection of the time delay between fs and ns laser pulses allows the latter to interact selectively with different parts of the NPs plume, controlling, to a certain degree, the reduction of the NPs size and dispersion. Another original effect of the UV laser irradiation is the change in the deposited films topology, due to a reduction of the NP-aggregates density and size, fostering non-uniform dense assemblies of NPs with concentration well above the percolation threshold, with the consequent reduction of the influence of the exchange interactions on the macroscopic magnetic properties. The magnetic behavior of the films prepared using two laser beams with respect to that obtained in the case of fs-PLD only is characterized by higher H(c) values (up to approximately 70%) and a good compromise between the hysteresis loops squareness and moderate exchange interactions, strongly correlated with the NPs topology.

Generation of high energy, 30 fs pulses at 527 nm by hollow-fiber compression technique.

The compression of 300-fs-long, chirp-free laser pulses at 527 nm down to 30 fs is reported. The laser pulses, originated from a frequency-doubled, mode-locked Nd:glass laser, were compressed by a 0.7-m-long, 150-microm-bore-diameter, argon-filled hollow fiber, and a pair of SF10 prisms with a final energy of 160 microJ. These are the shortest, high energy pulses ever produced by direct pulse compression at the central wavelength of 527 nm. The spectral broadening of the pulses propagating inside the hollow fiber was experimentally examined for various filling-gas pressures and input pulse energies. The spectral width of the pulses was broadened up to 25 nm, and 27 nm for argon- and krypton-filled hollow fiber, respectively, at a gas pressure lower than 2 bar. The physical limitations of the hollow-fiber pulse compression technique applied in the visible range are also studied.

Analgesic properties of electromagnetic field therapy in patients with chronic pelvic pain.

AIM: Demonstration of analgesic effects of electromagnetic field treatment in cases of chronic refractory pelvic pain. STUDY DESIGN: Prospective non-controlled trial, 64 women complaining about pelvic pain of at least 6 months duration, resistant to standard therapies, submitted to electromagnetic field applications on both iliac regions by Thelf Systems apparatus by two applications daily lasting 2 hours each for 20-40 days. Control visit after 3 months. RESULTS: Complete subsidence of pain in 39 cases (61%), in 15 patients (23%) relief during treatment, then mild endopelvic tension after a 3-month control; in 10 cases (16%) symptoms reduced only during application hours, unchanged at follow-up. Outcome of treatment appears to be independent of pre-existent psychosocial variables. CONCLUSION: Magnetic therapy shows a real analgesic effect on pelvic pain, and seems to contribute to resolution of complex interactions between somatic nociceptive stimuli and psychosocial implications affecting pain perception in these patients.

Hollow-fiber compression of visible, 200 fs laser pulses to 40 fs pulse duration.

We demonstrate the use of a very simple, compact, and versatile method, based on the hollow-fiber compression technique, to shorten the temporal length of visible laser pulses of 100-300 fs to pulse durations shorter than approximately 50 fs. In particular, 200 fs, frequency-doubled, Nd:glass laser pulses (527 nm) were spectrally broadened to final bandwidths as large as 25 nm by nonlinear propagation through an Ar-filled hollow fiber. A compact, dispersive, prism-pair compressor was then used to produce as short as 40 fs, 150 microJ pulses. A very satisfactory agreement between numerical simulations and measurements is found.

Phenolphthalein induces chromosome aberrations in human and Chinese hamster liver cells (CHEL) cultured in vitro.

Phenolphthalein is a nonprescription laxative agent that has been widely used during this century. Recent studies in animal models have shown that phenolphthalein has carcinogenic activity. In order to assess cytogenetic effects on human cells in vitro, we tested phenolphthalein in a chromosome aberration assay in human embryo cells derived from amniotic fluid. Our results show that phenolphthalein induces a significant increase in the frequency of chromosome aberrations in human cells. The lowest dose level at which the clastogenic effect is evident is 23.2 microg/ml. Similar positive results were obtained in a Chinese hamster liver cell line, which is metabolically competent to activate different classes of promutagens and procarcinogens into biologically active metabolites. Instead, parallel experiments in Chinese hamster ovary cells did not show any clastogenic effect due to phenolphthalein. These latter data suggested that phenolphthalein acts as a promutagen and must be metabolically activated to exert its clastogenic effect. Teratogenesis Carcinog. Mutagen. 20:209-217, 2000.