RESUMO
We present laser-based methane detection near 1651 nm inside an antiresonant hollow-core fiber (HCF) using photothermal spectroscopy (PTS). A bismuth-doped fiber amplifier capable of delivering up to more than 160 mW at 1651 nm is used to boost the PTS signal amplitude. The design of the system is described, and the impact of various experimental parameters (such as pump source modulation frequency, modulation amplitude, and optical power) on signal amplitude and signal-to-noise ratio is analyzed. Comparison with similar PTS/HCF-based systems is presented. With 1.3 m long HCF and a fiber amplifier for signal enhancement, this technique is capable of detecting methane at single parts-per-million levels, which makes this robust in-fiber sensing approach promising also for industrial applications such as, e.g., natural gas leak detection.
RESUMO
For the first time, we report on the fabrication of a bend-insensitive single-mode bismuth (Bi)-doped $ {{\rm P}_2}{{\rm O}_5} {-} {{\rm SiO}_2} $P2O5-SiO2 fiber having a depressed cladding design and study its gain characteristics at a spectral region of 1.3-1.4 µm. It was shown that the obtained Bi-doped fiber can efficiently operate in the spectral band even at a bend radius of 1.5 cm. In addition, it was shown that this type of fiber has a smaller mode-field diameter in comparison with a step-index single-mode Bi-doped $ {{\rm P}_2}{{\rm O}_5} {-} {{\rm SiO}_2} $P2O5-SiO2 fiber with $ \Delta {n} \approx 0.006 $Δn≈0.006 that resulted in a decrease of saturation power and, as a consequence, in a reduction of the total pump power required to a high-level-gain operation. The laser and gain experiments show the possibility of the construction of a compact high-performance optical amplifier for O-band based on the depressed-cladding Bi-doped fiber.
RESUMO
In this paper, we report the performance of a bismuth-doped fiber amplifier at 1687 nm. This wavelength region is particularly interesting for laser-based spectroscopy and trace gas detection. The active bismuth-doped fiber is pumped at 1550 nm. With less than 10 mW of the seed power, more than 100 mW is obtained at the amplifier's output. We also investigate the signal at the output when a wavelength-modulated seed source is used, and present wavelength modulation spectroscopy of methane transition near 1687 nm. A significant baseline is observed in the spectra recorded when the fiber amplifier is used. The origin of this unwanted background signal is discussed and methods for its suppression are demonstrated.
RESUMO
We report experimental measurements and numerical calculations regarding the photostability of laser-active centers associated with bismuth (BACs) in Bi-doped GeO2-SiO2 glass fibers under pumping at 1550 nm at different temperatures. It was discovered that BACs are unstable under 1550-nm pumping when the temperature is elevated to hundreds of degrees centigrade. A simple numerical model was proposed to account for the discovered instability which turned out to be in good agreement with the experimental data.
RESUMO
The present study examined the levels of procaspases (zymogens of the main apoptosis enzymes, caspases) that are predicted based on application of the optimization principle. Optimization models have previously been successfully developed for many other physiological systems (e.g., circulation, oxygen transport system, fibrinolysis, and blood coagulation) but have not previously been applied to apoptotic biochemical pathways. Our model assumed that apoptotic pathways are designed to minimize protein consumption. Procaspase concentrations were predicted based on this assumption, along with known schemes of apoptosis reactions and kinetic constants for procaspase activation and target cleavage. Good agreement between the model predictions and actual procaspase levels was observed.
