Multi-channel delay sampling to extend imaging depth in high-speed swept-source OCT systems.

We present a multi-channel delay sampling method to extend imaging depth in high-speed swept-source optical coherence tomography (SS-OCT). A balanced detector captures interference signals, converting them into electrical signals, which are then split into N channels, each with fixed time delays determined by the length of electrical cables. Then, they are digitized by an N-channel acquisition card. A calibration procedure is utilized to compensate for non-uniform phase shifts resulting from fixed time delays. The N-channel signals are merged in k-space and resampled to obtain a linearized spectrum, which increases the sampling rate by a factor of N, thereby extending the ranging distance by N times, all without altering k-clock triggering or sacrificing other imaging performance. The signal-to-noise ratio and sensitivity within the original depth range also have been enhanced. This advancement contributes to the improvement of the overall performance of SS-OCT systems.

Plasma-Assisted Chemical-Looping Combustion: Low-Temperature Methane and Ethylene Oxidation with Nickel Oxide.

The chemical reaction network of low-temperature plasma-assisted oxidation of methane (CH4) and ethylene (C2H4) with nickel oxide (NiO) was investigated in a heated plasma reactor through time-dependent species measurements by electron-ionization molecular beam mass spectrometry (EI-MBMS). Methane (ethylene) oxidation by NiO was explored in temperature ranges from 300-700 °C (300-500 °C) and 300-800 °C (300-600 °C) for the plasma and nonplasma conditions. Significant enhancement of methane oxidation was observed with plasma between 400 and 500 °C, where no oxidation was observed under nonplasma conditions. For the oxidation of methane at higher temperatures, three different oxidation stages were observed: (I) a period of complete oxidation, (II) a period of incomplete CO oxidation, and (III) a period of carbon buildup. For the C2H4 experiments, and unlike the CH4 experiments, the plasma resulted in a significant amount of new intermediate oxygenated species, such as CH2O, CH3OH, C2H4O, and C2H6O. Carbon deposits were observed under both methane and ethylene conditions and verified by X-ray photoelectron spectroscopy (XPS). ReaxFF (reactive force field) simulations were performed for the oxidation of CH4 and C2H4 in a nonplasma environment. The simulated intermediates and products largely agree with the species measured in the experiments, though the predicted intermediate oxygenated species such as CH2O and C2H6O were not observed in experiments under nonplasma conditions. A reaction pathway analysis for CH4 and C2H4 reacting with NiO was created based on the observed species from the MBMS spectra along with ReaxFF simulations.