Broadband External-Cavity Diode Laser

A broadband external-cavity diode laser (ECDL) has been invented for use in spectroscopic surveys preparatory to optical detection of gases. Heretofore, commercially available ECDLs have been designed, in conjunction with sophisticated tuning assemblies, for narrow- band (and, typically, single-frequency) operation, as needed for high sensitivity and high spectral resolution in some gas-detection applications. However, for preparatory spectroscopic surveys, high sensitivity and narrow-band operation are not needed; in such cases, the present broadband ECDL offers a simpler, less-expensive, more-compact alternative to a commercial narrowband ECDL

Internal Water Vapor Photoacoustic Calibration

Water vapor absorption is ubiquitous in the infrared wavelength range where photoacoustic trace gas detectors operate. This technique allows for discontinuous wavelength tuning by temperature-jumping a laser diode from one range to another within a time span suitable for photoacoustic calibration. The use of an internal calibration eliminates the need for external calibrated reference gases. Commercial applications include an improvement of photoacoustic spectrometers in all fields of use

Results of a Long-Term Demonstration of an Optical Multi-Gas Monitor on ISS

Previously at SAMAP we reported on the development of tunable diode laser spectroscopy (TDLS) based instruments for measuring small gas molecules in real time. TDLS technology has matured rapidly over the last 5 years as a result of advances in low power diode lasers as well as better detection schemes. In collaboration with two small businesses Vista Photonics, Inc. and Nanoracks LLC, NASA developed a 4 gas TDLS based monitor for an experimental demonstration of the technology on the International Space Station (ISS). Vista invented and constructed the core TDLS sensor. Nanoracks designed and built the enclosure, and certified the integrated monitor as a payload. The device, which measures oxygen, carbon dioxide, ammonia and water vapor, is called the Multi-Gas Monitor (MGM). MGM measures the 4 gases every few seconds and records a 30 second moving average of the concentrations. The relatively small unit draws only 2.5W. MGM was calibrated at NASA-Johnson Space Center in July 2013 and launched to ISS on a Soyuz vehicle in November 2013. Installation and activation of MGM occurred in February 2014, and the unit has been operating nearly continuously ever since in the Japanese Experiment Module. Data is downlinked from ISS about once per week. Oxygen and carbon dioxide data is compared with that from the central Major Constituents Analyzer. Water vapor data is compared with dew point measurements made by sensors in the Columbus module. The ammonia channel was tested by the crew using a commercial ammonia inhalant. MGM is remarkably stable to date. Results of 18 months of operation are presented and future applications including combustion product monitoring are discussed

Wavelength-Agile External-Cavity Diode Laser for DWDM

A prototype external-cavity diode laser (ECDL) has been developed for communication systems utilizing dense wavelength- division multiplexing (DWDM). This ECDL is an updated version of the ECDL reported in Wavelength-Agile External- Cavity Diode Laser (LEW-17090), NASA Tech Briefs, Vol. 25, No. 11 (November 2001), page 14a. To recapitulate: The wavelength-agile ECDL combines the stability of an external-cavity laser with the wavelength agility of a diode laser. Wavelength is modulated by modulating the injection current of the diode-laser gain element. The external cavity is a Littman-Metcalf resonator, in which the zeroth-order output from a diffraction grating is used as the laser output and the first-order-diffracted light is retro-reflected by a cavity feedback mirror, which establishes one end of the resonator. The other end of the resonator is the output surface of a Fabry-Perot resonator that constitutes the diode-laser gain element. Wavelength is selected by choosing the angle of the diffracted return beam, as determined by position of the feedback mirror. The present wavelength-agile ECDL is distinguished by design details that enable coverage of all 60 channels, separated by 100-GHz frequency intervals, that are specified in DWDM standards

Laser Spectroscopy Multi-Gas Monitor: Results of Technology Demonstration on ISS

Tunable diode laser spectroscopy (TDLS) is an up and coming trace and major gas monitoring technology with unmatched selectivity, range and stability. The technology demonstration of the 4 gas Multi-Gas Monitor (MGM), reported at the 2014 ICES conference, operated continuously on the International Space Station (ISS) for nearly a year. The MGM is designed to measure oxygen, carbon dioxide, ammonia and water vapor in ambient cabin air in a low power, relatively compact device. While on board, the MGM experienced a number of challenges, unplanned and planned, including a test of the ammonia channel using a commercial medical ammonia inhalant. Data from the unit was downlinked once per week and compared with other analytical resources on board, notably the Major Constituent Analyzer (MCA), a magnetic sector mass spectrometer. MGM spent the majority of the time installed in the Nanoracks Frame 2 payload facility in front breathing mode (sampling the ambient environment of the Japanese Experiment Module), but was also used to analyze recirculated rack air. The capability of the MGM to be operated in portable mode (via internal rechargeable lithium ion polymer batteries or by plugging into any Express Rack 28VDC connector) was a part of the usability demonstration. Results to date show unprecedented stability and accuracy of the MGM vs. the MCA for oxygen and carbon dioxide. The ammonia challenge (approx. 75 ppm) was successful as well, showing very rapid response time in both directions. Work on an expansion of capability in a next generation MGM has just begun. Combustion products and hydrazine are being added to the measurable target analytes. An 8 to 10 gas monitor (aka Gas Tricorder 1.0) is envisioned for use on ISS, Orion and Exploration missions

Discrete wavelength-locked external cavity laser

An external cavity laser (and method of generating laser light) comprising: a laser light source; means for collimating light output by the laser light source; a diffraction grating receiving collimated light; a cavity feedback mirror reflecting light received from the diffraction grating back to the diffraction grating; and means for reliably tuning the external cavity laser to discrete wavelengths

Matelda in the Terrestrial Paradise

This analysis of the enigmatic figure of Matelda, guardian of the Terrestrial Paradise in Dante's Purgatorio, considers both the unresolved question of Matelda's historical identity, in particular whether Dante is alluding to the historical personage, Countess Matilda of Tuscany (1046-1115), and the numerous critical glosses that have emerged over the years, whereby Matelda has been interpreted as a symbolic figure, for example, as the biblical typology of the active/contemplative life, as the representation of human wisdom, or in a variety of other symbolic guises. Whilst alluding to recognisable idyllic poetic images, such as the donna angelicata of the vernacular tradition, Dante's conceptualisation of Matelda is nevertheless aligned to the pilgrim-poet's own development in via of a redemptive poetics in which the writer articulates an urgent message of reform, at both the secular and ecclesiastical levels. The linking of Matelda with the notion of the loss of the prelapsarian state of humankind's innocence and her supervision of the penitential cleansing rites performed on Dante-protagonist, in anticipation of his ascent to Paradise in the company of Beatrice, represent crucial moments in Dante's mapping out of prudential history for his readers and his call for a recovery of Christian values

Portable Multigas Monitors for International Space Station

The Environmental Health System (EHS) on International Space Station (ISS) includes portable instruments to measure various cabin gases that acutely impact crew health. These hand-held devices measure oxygen, carbon dioxide, carbon monoxide, hydrogen chloride and hydrogen cyanide. The oxygen and carbon dioxide units also serve to back up key functions of the Major Constituent Analyzers. Wherever possible, commercial off-the-shelf (COTS) devices are employed by EHS to save development and sustaining costs. COTS hardware designed for general terrestrial applications however has limitations such as no pressure compensation, limited life of the active sensor, calibration drift, battery issues, unpredictable vendor support and obsolescence. The EHS fleet (inflight and ground inventory) of instruments is both aging and dwindling in number. With the retirement of the US Space Shuttle, maintenance of on-orbit equipment becomes all the more difficult. A project is underway to search for gas monitoring technology that is highly reliable and stable for years. Tunable Diode Laser Spectroscopy (TDLS) seems to be the front-runner technology, but generally is not yet commercially available in portable form. NASA has fostered the development of TDLS through the Small Business Innovative Research (SBIR) program. A number of gases of interest to the aerospace and submarine communities can be addressed by TDLS including the list mentioned above plus hydrogen fluoride, ammonia and water (humidity). There are several different forms of TDLS including photoacoustic and direct absorption spectroscopy using various multipass cell geometries. This paper describes the history of portable gas monitoring on NASA spacecraft and provides a status of the development of TDLS based instruments. Planned TDLS flight experiments on ISS could lead both to operational use on ISS and important roles in future Exploration spacecraft and habitats

The Promised Land: A Postcolonial Homiletic of Promise in the Asian American Context

Asian American Christians carry within them a triple consciousness by being Asian, American, and Christian. Being Christian specifically means being a pilgrim bound for the Promised Land. The Asian American pilgrim preacher’s message issues from this triple consciousness and from a spirit of postcolonial liberation. Such a preacher’s message is therefore a declaration or assurance of God’s liberative promise of the Promised Land for Asian Americans, the Land already being realized here and now in the foreign land. By being this-earthly and other-worldly, the pilgrim preacher’s message is synthetic-ethical in nature. This article shows that the triple consciousness is a further development of biblical and Augustinian idea/ideals of the Christian believer’s pilgrimage

An Annotated Checklist of Wisconsin Mutillidae (Hymenoptera)

A survey of Wisconsin velvet ants (Hymenoptera: Mutillidae) conducted from literature searches, collection inventories, and two years of field work (2001-2002) yielded 28 species in three subfamilies. Of these, 23 species (representing 82% of the Wisconsin fauna and a 460% increase in the known species richness) are new state species records, having not previously been recorded in the published literature from the state. The known distributions of all Wisconsin species are reported by region and county, along with pertinent phenological, natural history, and other collection information, when known