We are developing a mid-IR ICL-based sensor for field measurements of ambient CH<sub>4</sub>. We describe some of the design considerations for this sensor. Our sensor uses a Type II Quantum Cascade Laser (or Interband Cascade Laser, ICL) operating near 3.3 μm to monitor a well-isolated line in the υ<sub>3</sub> fundamental band of CH<sub>4</sub>. The ICL operates in cw mode at cryogenic temperature. The sensor consists of two major components, an optical breadboard containing the laser, transfer optics, sample cell, and detectors, and an instrumentation module containing power supplies and system control computer. Light from the laser is collimated using a reflective microscope objective and transported to a multipass cell via a simple optics train. The multipass cell provides an optical path of ~7 meters in an 0.25 m base path. The spectrometer uses TE-cooled InAs detectors along with our Balanced Ratiometric Detection. Our measured precision for CH<sub>4</sub> is 15 ppbv for a 60 sec integration time. We report on additional sensor characterization and data from recent field trials at two facilities maintained by the University of New Hampshire.
Mid infrared Quantum Cascade (QCL) and Interband Cascade Lasers (ICL) coupled with cavity-enhanced techniques, have proven to be sensitive optical diagnostic tools for both atmospheric sensing as well as breath analysis. In this work, a TE-cooled, pulsed QCL and a cw ICL are coupled to high finesse cavities, for trace gas measurements of nitric oxide, carbon dioxide, carbon monoxide and ethane. QCL's operating at 5.26 μm and 4.6 μm were used to record ICOS spectra for NO, CO<sub>2</sub>, and CO. ICOS spectra of C<sub>2</sub>H<sub>6</sub> were recorded at 3.35 μm using an ICL. Ringdown decay times on the order to 2-3 μs are routinely obtained for a 50 cm cavity resulting in effective pathlengths on the order of 1000 meters. The sample cell is compact with a volume of only 60ml. Details of the QCL and ICL cavity enhanced spectrometers are presented along with the detection results for trace gas species. Here we report a detection limit of 0.7 ppbv in 4 s for NO in simulated breath samples as well as human breath samples. A preliminary detection limit of 250 pptv in 4 s for CO is obtained and 35 ppb in 0.4 s for C<sub>2</sub>H<sub>6</sub>.
Recent advances in current-pumped, bandgap-engineered semiconductor lasers have dramatically impacted laser-based sensor concepts for in-situ trace species measurement and standoff sensing applications. These devices allow a common technology platform to access strong fundamental vibrational absorption transitions of many gases, liquids, and solids in the mid-wave and long-wave IR, as well as far-IR, or THz. The THz wavelength region is particularly interesting for applications related to structure penetrating detection of hidden materials and biomolecular spectroscopy. This presentation will briefly review the important properties of these lasers as they apply to sensor design and present highlights of recent sensor development activity for trace gas analysis in environmental and biomedical applications, remote sensing LIDAR systems, and detection of hidden explosives.
In this paper we discuss several sensitive diagnostics that have specifically developed for application to COIL and other iodine laser concepts such as AGIL and DOIL. We briefly cover the history of some important diagnostics including recently-developed diode laser sensors for a variety of parameters including: water vapor concentration, singlet oxygen yield, small signal gain, and translational temperature. We also discuss new developments and extensions of prior capabilities including: an ultra-sensitive diagnostic for I<sub>2</sub> dissociation, a new monitor for singlet oxygen yield, and a novel diode laser-based imaging system for simultaneous, multipoint spatial distributions of species concentration and temperature. Finally, we mention how these diagnostics have bee successfully applied to the emerging DOIL technology.
In this paper we discuss the application of sensitive, non-intrusive diagnostic techniques to characterize species in the flow that are critical for chemical oxygen iodine laser (COIL) devices and the electric discharge oxygen iodine laser (DOIL) concept. The key diagnostics include chemiluminescence to detect O<sub>2</sub>(a,b) and I(<sup>2</sup>P<sub>1/2</sub>) and tunable diode laser absorption measurements of I* and temperature. We have characterized variations in O and O<sub>2</sub>(a) yields with discharge power and oxygen mole fraction. We observe O<sub>2</sub>(a) yields to increase dramatically with decreasing oxygen mole fraction. We also discuss the application of a novel imaging diagnostic to obtain 2-D images of species concentrations and temperature.
In this paper we discuss vibrational to electronic energy transfer as a potential method for producing a population inversion in atomic iodine. We discuss the background of this approach and a novel, high-flux F atom source integrated into a small scale supersonic reactor. We present data for energy transfer from HF(v) and H<sub>2</sub>(v) to the I atom manifold. Using a sensitive diode laser diagnostic we have probed the ground state manifold atomic iodine and observed that the absorption on the I atom line could be reduced to an immeasureably low value. We also describe a novel, diode laser based imaging diagnostic that will have important applications in future chemical or electrical laser development.