ABSTRACT
Femtosecond laser-induced breakdown spectroscopy (fs-LIBS) is employed to detect tiny amounts of mass ablated from macroscopic specimens and to measure chemical images of microstructured samples with high spatial resolution. Frequency-doubled fs-pulses (length 400 fs, wavelength 520 nm) are tightly focused with a Schwarzschild microscope objective to ablate the sample surface. The optical emission of laser-induced plasma (LIP) is collected by the objective and measured with an echelle spectrometer equipped with an intensified charge-coupled device camera. A second fs-laser pulse (1040 nm) in orthogonal beam arrangement is reheating the LIP. The optimization of the experimental setup and measurement parameters enables us to record single-pulse fs-LIBS spectra of 5 nm thin metal layers with an ablated mass per pulse of 100 femtogram (fg) for Cu and 370 fg for Ag films. The orthogonal double-pulse fs-LIBS enhances the recorded emission line intensities (two to three times) and improves the contrast of chemical images in comparison to single-pulse measurements. The size of ablation craters (diameters as small as 1.5 µm) is not increased by the second laser pulse. The combination of minimally invasive sampling by a tightly focused low-energy fs-pulse and of strong enhancement of plasma emission by an orthogonal high-energy fs-pulse appears promising for future LIBS chemical imaging with high spatial resolution and with high spectrochemical sensitivity.
ABSTRACT
BACKGROUND: Studies have shown that suicidal individuals who use the Internet for suicide-related purposes are more suicidal than nonsuicide-related users, but evidence from European countries is lacking. AIMS: We assessed differences between suicidal individuals who go online for suicide-related purposes and other suicidal individuals in Austria. METHOD: Participants were 53 individuals aged between 18 and 24 years who felt suicidal in the past year and completed an anonymous online survey. RESULTS: Individuals who went online for suicide-related purposes were more suicidal, and more depressed, compared with individuals who did not use the Internet for suicide-related purposes. There were no large differences with regard to social anxiety and perceived barriers for help-seeking between the two groups. CONCLUSION: This study finds that suicidal online users are more depressed and suicidal than nonusers in a sample from Central Europe. Online interventions to combat depression and suicidality need to be strengthened to reach out to this important target population.
