Angular dependence of filament-induced plasma emission from a GaAs surface.

Quantitative measurements of the angular distribution of the plasma line emission from a gallium arsenide (GaAs) target irradiated by a single laser-air filament are reported. These enable reliable estimates of the stand-off ranges possible with single-filament-induced laser-induced breakdown spectroscopy materials detection.

Study of filamentation threshold in zinc selenide.

The possibility of creating filaments with laser wavelengths ranging from 800 nm to 2.4 µm was investigated using an OPA laser system. Zinc Selenide's (ZnSe) unique characteristics - small band gap E(gZnSe)=2.67eV and positive dispersion for this wavelength range - are well suited for filamentation study where multi-photon absorption can be achieved with two to six photons.

Kilometer range filamentation.

We demonstrate for the first time the possibility to generate long plasma channels up to a distance of 1 km, using the terawatt femtosecond T&T laser facility. The plasma density was optimized by adjusting the chirp, the focusing and beam diameter. The interaction of filaments with transparent and opaque targets was studied.

Tensile and shear bond strength evaluation of a total-etch three-step and two self-etching one-step dentin bonding systems.

PURPOSE: The aim of this study was to compare the bond strengths of two new self-etching one-step (Prompt L-Pop 2 and Adper Prompt L-pop) to a total-etch three-step dentin bonding system (Scotchbond Multipurpose Plus). MATERIALS AND METHODS: One hundred twenty human molars were randomly divided into 3 groups of 40 specimens each. Dentin surfaces of each group were bonded with either Scotchbond Multipurpose Plus (SMP), a three-step system, Prompt L-Pop 2 (PLP), or Adper Prompt L-Pop (APLP), two one-step bonding systems--according to manufacturers' recommendations. After adhesive application, a composite resin cylinder was incrementally built in a Teflon mold (5 mm high and 5 mm in diameter). The samples of each group were randomly divided into 2 subgroups of 20 samples each and were tested in a shear bond or in a tensile bond strength mode (crosshead speed 5 mm/min). Statistical analyses were performed with one-way ANOVA and Student's t-test. RESULTS: The significantly lowest shear and tensile bond strength values were obtained with APLP. PLP revealed higher shear bond strengths than APLP and SMP. There were no differences in tensile bond strengths between PLP and SMP (p < 0.05). CONCLUSION: The results of this in vitro study showed that the chemical modifications (adjunction of monomers and copolymers) of the self-etching all-in-one system APLP did not improve its mechanical properties.

Dramatic enhancement of supercontinuum generation in elliptically-polarized laser filaments.

Broadband laser sources based on supercontinuum generation in femtosecond laser filamentation have enabled applications from stand-off sensing and spectroscopy to the generation and self-compression of high-energy few-cycle pulses. Filamentation relies on the dynamic balance between self-focusing and plasma defocusing - mediated by the Kerr nonlinearity and multiphoton or tunnel ionization, respectively. The filament properties, including the supercontinuum generation, are therefore highly sensitive to the properties of both the laser source and the propagation medium. Here, we report the anomalous spectral broadening of the supercontinuum for filamentation in molecular gases, which is observed for specific elliptical polarization states of the input laser pulse. The resulting spectrum is accompanied by a modification of the supercontinuum polarization state and a lengthening of the filament plasma column. Our experimental results and accompanying simulations suggest that rotational dynamics of diatomic molecules play an essential role in filamentation-induced supercontinuum generation, which can be controlled with polarization ellipticity.

The antibody response to hepatitis B virus vaccination is negatively influenced by the hepatitis C virus viral load in patients with chronic hepatitis C: a case-control study.

The purpose of this work was to evaluate in a case-control study the immunogenicity of a recombinant hepatitis B virus (HBV) vaccine in patients with chronic hepatitis C. Seventy-seven patients with histologically proven chronic hepatitis C without cirrhosis were included in a prospective trial and matched for sex and age to 231 healthy adult subjects. Recombinant HBV vaccine was administered at a dose of 20 microg at months 0, 1 and 2. The definition of 'responder to vaccination' was anti-HBs titre > 10 mIU/ml after the three injections. Forty-nine (63.6%) chronic hepatitis C patients were responders to vaccination, compared with 217 (93.9%) controls (P < 0.0001). After the three injections, anti-HBs titres were 156 +/- 260 and 615 +/- 435 mIU/ml (P < 0.0001), respectively. Chronic hepatitis C patients who were non-responders to vaccination had significantly higher viral load than responders to vaccination. Moreover, a negative correlation was observed between viral load and anti-HBs concentration (r = -0.36, P = 0.003). No significant side effects were observed. There was no effect of vaccination on alanine aminotransferase (ALT) levels and hepatitis C virus (HCV) viral load during or after vaccination. In multivariate analysis, the main predictive factors of response to HBV vaccine were absence of anti-HCV antibodies (OR = 7.65, P < 0.0001), weight < 75 kg (OR = 1.99, P < 0.035), and age < 50 years (OR = 1.58, P < 0.082). Our results suggest that viral load seems to negatively influence the response to HBV vaccine.

Transition from linear- to nonlinear-focusing regime in filamentation.

Laser filamentation in gases is often carried out in the laboratory with focusing optics to better stabilize the filament, whereas real-world applications of filaments frequently involve collimated or near-collimated beams. It is well documented that geometrical focusing can alter the properties of laser filaments and, consequently, a transition between a collimated and a strongly focused filament is expected. Nevertheless, this transition point has not been identified. Here, we propose an analytical method to determine the transition, and show that it corresponds to an actual shift in the balance of physical mechanisms governing filamentation. In high-NA conditions, filamentation is primarily governed by geometrical focusing and plasma effects, while the Kerr nonlinearity plays a more significant role as NA decreases. We find the transition between the two regimes to be relatively insensitive to the intrinsic laser parameters, and our analysis agrees well with a wide range of parameters found in published literature.