Intra-cavity spectroscopy using amplified spontaneous emission in fiber lasers

Fiber laser sources offer interesting possibilities for gas sensors since they can operate over an extended wavelength range, encompassing the near-IR absorption lines of a number of important gases but a major problem is that overtone absorption lines of gases in the near-IR are relatively weak. In order to enhance sensitivity, we present here a simple method of intra-cavity absorption spectroscopy (ICAS) which makes use of the amplified spontaneous emission (ASE) already present within a fiber laser cavity. The ASE also provides a convenient broadband source for the simultaneous interrogation of several gases within the gain-bandwidth of the fiber laser. The key principle is based on adjusting the cavity attenuation to select an appropriate inversion level where the fiber gain curve is flat. Under this condition, the ASE undergoes multiple circulations within the fiber laser cavity, enhancing the effective path-length of a gas cell placed within the laser cavity. A theoretical model of system operation is given and we have experimentally demonstrated the principle of operation with acetylene and carbon dioxide using a simple erbium fiber laser system containing a 6 cm path-length, fiber coupled, intra-cavity, micro-optic gas cell. We have experimentally simultaneously observed 16 absorption lines for 1% acetylene gas in the 1530 nm region and detected the very weak carbon dioxide lines in this same wavelength region. A path length enhancement of in the linear regime has been demonstrated transforming the 6 cm micro-optic cell into an effective path length of m. We also demonstrate how the enhancement factor may be calibrated by use of a simple fiber-optic interferometer. Apart from the OSA, all components are inexpensive and the system is very simple to construct and operate

X-Ray Emission from the Supergiant Shell in IC 2574

The M81 group member dwarf galaxy IC 2574 hosts a supergiant shell of current and recent star-formation activity surrounding a 1000 x 500 pc hole in the ambient Hi gas distribution. Chandra X-ray Observatory imaging observations reveal a luminous, L_x ~ 6.5 x 10^{38} erg/s in the 0.3 - 8.0 keV band, point-like source within the hole but offset from its center and fainter diffuse emission extending throughout and beyond the hole. The star formation history at the location of the point source indicates a burst of star formation beginning ~25 Myr ago and currently weakening and there is a young nearby star cluster, at least 5 Myr old, bracketing the likely age of the X-ray source at between 5 and ~25 Myr. The source is thus likely a bright high-mass X-ray binary --- either a neutron star or black hole accreting from an early B star undergoing thermal-timescale mass transfer through Roche lobe overflow. The properties of the residual diffuse X-ray emission are consistent with those expected from hot gas associated with the recent star-formation activity in the region.Comment: 5 pages, accepted for publication in the Astrophysical Journal Letter

Viability for oxidation of H2S gas using low concentration solutions of H2O2 peroxide in applications for biogas purification.

This thesis is an examination of the viability of a low pH hydrogen peroxide scrubbing process for removing H 2 S acid gas present in typical biogas streams generated from dairy farm anaerobic digesters. Biogas ranges in composition based on the feedstock manure used in the anaerobic digestion process but typically consists of methane (50-60%), carbon dioxide (40-50%), and trace amounts of hydrogen sulfide and ammonia. Hydrogen sulfide is of prime concern because it is an odorous, poisonous, and highly corrosive gas which can impede use in power generation applications for biogas such as boilers, internal combustion engines, microturbines, fuel cells, and stirling engines. Thus, removal of hydrogen sulfide is highly recommended. Desirable attributes for a gas purification system include low capital cost, low operational costs, minimal preventative maintenance, minimum energy inputs, and ease of use. H 2 O 2 is a highly selective oxidant that does not produce toxic and corrosive by-products and has been shown to be a convenient way of eliminating oxidizable pollutants such as hydrogen sulfide gas from air or other gas streams. Based on these criteria, an experimental approach was used to investigate the feasibility of using an acidic H 2 O 2 scrubber for the removal of H 2 S from synthetic biogas. Two test reactors were constructed, each setup with multiple configurations of packing volume, H 2 O 2 concentration, and liquid volume. Synthetic biogas was introduced into the reactors and data was collected including liquid pH, liquid oxidation reduction potential, and H 2 S concentration of exit gas during experiments. In total there were over twenty separate experiments conducted between the bench scale experiments, 1st scrubber trials, and 2nd scrubber trials. The results of these experiments demonstrate that a low pH H 2O 2 scrubbing system shows commercial viability for the removal of H 2 S from biogas. Functional oxidation of H 2 S was achieved with removal efficiencies of 99% in certain reactor configurations. Bench scale experiments indicate that highest oxidation reduction potential of hydrogen peroxide solutions occurs in the acidic pH range between pH 3-5. Key operating parameters observed for functional oxidation of H 2 S gas were the bubble diameter of inlet biogas and gas residence time. Increased residence times and smaller mean inlet bubble diameters led to maximum removal efficiencies. The research was conducted in the University of Louisville Food Processing Laboratory and used as proof-of-concept for claims made in United States Patent Application 20090130008. These initial results indicate that future work is warranted for examining suitability of using a commercial scale acidic hydrogen peroxide scrubbing vessel as an H 2 S removal technology in biogas purification