Physical Sciences Inc. is developing an advanced, compact LIDAR capable of continuous mapping of atmospheric extinction to provide environmental situational awareness for high energy laser weapon operations by the Navy. The LIDAR uses a MicroPulse LIDAR architecture and combines a solid state Nd:YLF laser operating at 1 micron with photon counting detectors and advanced aerosol retrieval algorithms. We report on the design of the engineering prototype and provide a summary of the system performance demonstrated during the Comprehensive Atmospheric Boundary Layer Extinction / Turbulence Refinement eXperiment conducted at the Shuttle Landing Facility at Kennedy Space Center in June, 2017.
Two areas of current activity in the Earth sciences are the development of ground-based sensor networks and sensor
payloads for unmanned aircraft. This paper reviews a few of our sensor development efforts, highlighting how design
elements meet specific sensor measurement needs.
In this presentation we report on our progress in developing a small, lightweight and low power consumption
carbon monoxide sensor for detection and post-fire cleanup aboard manned spacecraft. The sensor is a laser-based
absorption spectrometer that uses a Quantum Cascade Laser (QCL) operating at 4.61 microns. The target sensitivity for
post-fire cleanup applications is 1 to 500 ppmv. The presentation will detail the laser design and performance and the
bench-top performance of the TDLAS sensor including sensitivity and Allan variance measurements. The status of the
prototype sensor including size, weight and power consumption estimates and measurements will be presented.
Tunable Diode Laser Absorption Spectroscopy (TDLAS) is finding ever increasing utility for industrial
process measurement and control. The technique's sensitivity and selectivity benefit continuous
concentration measurement of selected analytes in complex gas mixtures. Tradeoff options among optical
path length, absorption linestrength, linewidth, cross-interferences, and sampling methodology enable
sensor designers to optimize detection for specific applications. This paper describes TDLAS measurement
precision and accuracy limitations in emerging applications that demand increasing volumes of distributed
miniaturized sensors at diminishing costs. In these situations, the TDLAS specificity is a key attribute,
while high sensitivity enables novel sampling package designs with short optical pathlengths. Under these
circumstances, the traditional approaches to optimizing accuracy and precision may fail if analyzer control
features are sacrificed to reduce cost. We describe here a relatively simple TDLAS sensor designed to
meet the needs for acceptable cost, and discuss its theory of operation along with the implications on
measurement accuracy and precision.
We demonstrate a mid-IR semiconductor laser-based absorption spectrometer for field measurements of ambient CH4. The field 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 3 fundamental band of CH4. The ICL operates in cw mode at cryogenic temperatures. The sensor uses a multipass cell that provides an optical path of ~7 m with a 0.25-m base path. Thermoelectrically cooled InAs detectors are used along with balanced ratiometric detection to achieve a precision of 15 ppbv for a 60-s integration time. Several successful field demonstrations are carried out at sites maintained by the University of New Hampshire.
We are developing a mid-IR ICL-based sensor for field measurements of ambient CH4. 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 υ3 fundamental band of CH4. 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 CH4 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, CO2, and CO. ICOS spectra of C2H6 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 C2H6.
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.
12 Recent advances in mid-IR semiconductor laser technology based on intersubband transitions in InGaAs quantum wells promise a dramatic impact on tunable diode laser-based sensors for trace gases. This paper reports recent progress toward this realization of room-temperature laser-based sensors for combustion-generated pollutants such as NOx and SOx. Laboratory measurements of SO2 at 8.6 micrometers are presented with detection limits on the order of 1 ppm. Extensions of these approaches for higher sensitivity measurements in exhaust gas conditions are described, as well as measurements of SO3.
12 To address the inherent issues with extractive sampling, Air Liquide and PSI are collaborating on the development of an in-situ multi-functional near-IR tunable diode laser system. The system is specifically targeted for application in harsh combustion environments with flue gas temperatures > 1600 degree(s)C and high particle densities. The multiplexing capability of the diode laser system allows near simultaneous detection of CO, O2, and H2O. These are essential species in characterizing the combustion state of the process, i.e., fuel-rich or fuel-lean, and the flue gas temperature. Sensor development and testing are conducted on a 700 kW oxy-fuel pilot furnace to evaluate the performance under simulated industrial conditions. Here we present pilot test results for dynamic stoichiometry changes, effect of particle entrainment, and air infiltration monitoring.
With stricter environmental regulations, optimization of the combustion process for reduced pollutant emission and higher fuel efficiency has become an industry objective. To achieve these objectives, continuous monitoring of key processes parameters such as temperatures, fuel and oxidant input, and flue gas composition is required. For flue gas composition monitoring conventional extractive sampling techniques are typically used. However these techniques suffer from slow response time due to long sample lines and are sensitive to plugging problems when applied to particle-laden flows. Using in-situ monitoring with near-IR tunable diode lasers (TDL) eliminates the problems encountered with extractive sampling. The chemical species to be monitored dictates the wavelength range of the diode lasers used. These lasers are rapidly tuned over an absorption line to obtain concentration along the line-of-sight path. In addition, gas temperature can be measured by scanning the laser over multiple rotational lines of a target molecule. Here we demonstrate the feasibility of using TDL's for in-situ O2 monitoring on the exhaust end of Air Liquide's oxy-fuel pilot furnace. Tests were conducted at various operating conditions and compared with conventional extractive sampling measurements. The response time of the technique is demonstrated by measurements conducted on a dynamic system where the fuel flow is oscillated at low frequencies. In addition, to study the effect of dirty gas streams typically found on industrial processes, seed particles were introduced into the burner to simulate particle-laden flows.
New sensor concepts base don rapidly tunable, room- temperature diode laser absorption are being developed for a variety of aeropropulsion testing and control applications. The sensors are compact, rugged, capable of remote operation, and sensitive to a number of important control parameters. This paper describes recent progress in the development of three specific sensor platforms: inlet air mass flux for in-flight aeroengine control; simultaneous density, temperature, and velocity measurements in high- speed propulsion test facilities; and multi-species emissions monitoring. The measurement principles and system architectures are reviewed, along with sample laboratory and field test data.
Recent advances in room-temperature tunable diode lasers and ultrasensitive electronic noise quieting detection techniques now enable a new generation of compact, optoelectronic, ultrasensitive trace gas sensors. These advances are key to producing sensors capable of routine and extended field use. We achieve near shot noise-limited signal detection using a novel, balanced ratiometric detector (BRD) which permits measurements of absorbances of 1:106. High sensitivity is achieved by coupling this technology with an extended optical pathlength. The BRD is characterized by a wide linear dynamic range. A 10 Hz measurement rate enables ground level flux measurements or airborne concentration measurements. We will present an overview of two applications of our ultrasensitive detection technology to in situ atmospheric sensing. The first sensor is being developed to monitor boundary layer NO2 fluxes. This sensor operates at 670 nm, utilizes an open multipass optical cell, and has a sub-ppbv detection sensitivity. The second sensor is an airborne, near IR diode laser hygrometer. The sensor uses an in-situ air measurement probe housing a 50 cm, open optical path to circumvent problems inherent in extractive sampling. The sensor is capable of measuring water vapor throughout the troposphere and has a sensitivity of 0.5 ppmv at the tropopause.
Recent advances in room-temperature tunable diode lasers, fiberoptic beam transport, and sensitive detection strategies now permit in-stream sensing of numerous parameters relevant to aeropropulsion monitoring and control. These include density measurements of important flow constituents such as O2, H2O, CO2, and NOx. Based on path-averaged absorption measurements, the basic density measurements can be expanded to include other gasdynamic properties such as temperature and velocity. Simultaneous, multiparameter measurements allow determination of high order system parameters such as mass flux and thrust continuously and in real-time. This paper describes several sensor development efforts, exhaust mass flux, and emissions monitoring. Example measurements from laboratory configurations are presented along with performance projections for test-stand and flight systems. Integration issues with full-scale hardware and control opportunities are also discussed.
In this paper we discuss the potential advantages of the alexandrite laser as a light source for long range DOAS monitoring of air quality. The tunable alexandrite output can be frequency converted to provide essentially continuous coverage of the near UV spectrum. The wide tuning range and spectrally narrow output achieved by injection seeding are nearly ideal for several DOAS applications.