A principal R & D focus at Southwest Sciences since our founding in 1986 has been the use of diode lasers for laboratory spectroscopy and gas sensing applications. While some of our research has involved the use of lead-salt diode lasers operating at mid-infrared wavelengths, most of our recent work focuses on gas sensing applications utilizing near-infrared diode lasers that were originally developed for optoelectronic applications or fiber optic communications.
Our experience applying gas sensing to field measurements has taken us to many locations throughout the nation. Projects require making sensitive measurements in laboratories, factories, aboard aircraft, and outdoors. These real world measurements help our customers understand combustion, semiconductor processing, and atmospheric science.
Our recent research also includes work on development of new light sources at UV or IR wavelengths for spectroscopy, using nonlinear optical techniques. Also, we are using picosecond mode-locked Ti:Sapphire lasers in development of new laser diagnostics for combustion. Some of our current and recently completed projects are described below or in our recent publications.
- Atmosphere and the Environment
- Combustion and Fire Detection
- Medical Diagnostics and Imaging
- Non-Destructive Evaluation (NDE)
- Process Monitoring and Industrial Hygiene
- Electric and Magnetic Fields
- Spectroscopy and Technique Development
Airborne Humidity Measurements
Diode laser-based detection of water vapor provides a combination of high sensitivity, rapid time response, and wide dynamic range that is superior to most other methods of humidity measurement. Southwest Sciences is currently developing a fast (25 Hz) and accurate (5%) hygrometer for NSF's HIAPER Gulfstream-V aircraft. The instrument will measure water vapor over the entire range of the troposphere and lower stratosphere and does not require rack space or personnel onboard to operate. For details, see the HIAPER VCSEL Hygrometer page. Other past Southwest Sciences airborne humidity projects include instruments deployed on a KC-135 and a Lockheed 1011 aircraft. Contact: Mark Paige or Joel Silver.
Balloon-based trace gas sensors
Under DOE funding, Southwest Sciences is developing a lightweight (1 kg), low power (2 W), and precise (0.3 ppmv) instrument to measure carbon dioxide designed for standard weather balloons. By using a proprietary temperature and pressure-compensating reference cell, the instrument can measure carbon dioxide from the surface to the lower stratosphere. Test flights of the balloon-based carbon dioxide sensor are planned in 2006. The instrument uses low power and relatively inexpensive vertical cavity surface emitting lasers (VCSELs) combined with novel digital signal processors for data acquisition and analysis. A laboratory prototype water vapor sensor using similar technology can be operated off of a 30 cm x 30 cm solar cell. The water vapor hygrometer weighs just 230 g, including batteries, and measures water to part per million accuracy. Southwest Sciences is also investigating the feasibility of methane detection on balloon-based platforms under NSF funding. Contact: Joel Silver or Mark Paige
Measurement of Greenhouse Gas Fluxes
With funding from the Department of Energy, San Diego State University, and the NASA Ames Research Center, we have developed diode laser-based instrumentation for measurement of methane flux from natural and man-made sources. Using eddy correlation techniques combined with an open path optical design, we have measured methane fluxes from Arctic tundra and from a capped sanitary landfill. Our current efforts are focusing on reducing the cost of this type of instrumentation by development of new, customized digital signal processing methods and implementation of a novel multiple pass optical design that uses very inexpensive mirrors. In addition, Southwest Sciences is also researching the feasibility of a nitrous oxide flux instrument under USDA funding. Contact: Chris Hovde or Alan Stanton
Tropospheric Ammonia Detection
With support from the National Oceanic and Atmospheric Administration (NOAA), Southwest Sciences is developing two separate instruments for the detection of tropospheric ammonia. One instrument is designed for measurements of ammonia fluxes near source regions and is based upon a novel antimonide laser. The other instrument uses a miniature mass spectrometer in combination with chemical ionization techniques and is designed for light aircraft. Ammonia plays critical roles in aerosol particle formation, growth, and chemical composition, but the sources, sinks, and tropospheric distribution of ammonia are poorly known. Finally, Southwest Sciences is also examining the feasibility of open-path ammonia detection on airborne-based platforms via diode laser spectroscopy under DOE funding. Contact: Mark Paige (aircraft) or Chris Hovde(flux).
Measuring mass flow rate on a hypersonic rocket
Precise knowledge of air mass capture is the most crucial parameter in trimming hypersonic aircraft engines for maximum thrust, fuel efficiency, and stability. The air mass capture can be determined by a direct measurement of oxygen concentration and velocity. Southwest Sciences has developed diode laser instrument for this measurement. Oxygen concentration is measured by absorption spectroscopy, while velocity is determined from the Doppler shift of the spectrum. The system fits in the payload of a vehicle developed for the Hypersonic International Flight Research Experimentation (HiFIRE) program. The vehicle is mounted within a sounding rocket payload and reaches an apogee of about 300 km. The peak Mach number during the flight is about 7.8.
The optical mass capture (OMC) system is designed to be functional during both the ascent and descent phase of the flight path, below 30 km for maximum oxygen density. Rocket launches will occur in Woomera, Australia. Contact: Shin-Juh Chen
Measurement of Flame Species in Microgravity Combustion
Southwest Sciences has used fiber optic-coupled near-infrared diode lasers to measure water vapor or methane along eight lines of sight, with 0.1 second time resolution, in microgravity flames using the 2.2-second drop tower facility at the NASA Glenn Research Center. Current experiments are aimed at extending these measurements to molecular oxygen, but using an optical scanning system to obtain substantially improved spatial resolution. Contact: Joel Silver
Real Time Imaging of Flame Species in Microgravity Combustion
With support from the NASA Glenn Research Center, we are extending our earlier work on diode laser-based diagnostics of microgravity combustion. The objective of this project is to obtain 2-D time-resolved (15 Hz) images of water vapor, methane, and possibly the hydroxyl radical in microgravity combustion experiments conducted in the NASA Lewis drop tower facilities. High frequency wavelength modulation spectroscopy (WMS) is combined with a novel optical demodulation scheme. Contact: Kris Peterson.
Measurement of Combustion Radicals in Laboratory Flames
Under Department of Energy funding, we have used near-infrared diode lasers to measure the formyl radical (HCO) and the hydroxyl radical (OH) in low pressure laminar flat flames. Absorption-based measurements provide quantitative results for species concentrations that can be used for comparison with models of flame chemistry. A publication is in preparation. Contact: Mark Paige
Quantitative Species Measurements in Turbulent Combustion
With support from the Air Force Wright Laboratory we are developing a new laser diagnostic system for measurement of spatially and temporally resolved species concentrations in turbulent combustion. Our approach is based on picosecond pump/probe absorption measurements combined with an imaging optical lock-in detector. Contact: Joel Silver
Multigas Instrument for Testing of Fire Suppression Systems
Southwest Sciences is developing a multigas, multiple position diode laser based instrument for use inside combat vehicles during testing of fire suppression systems, under contract from the U. S. Army Aberdeen Proving Ground. The instrument will quantify simultaneously as many as seven gases, each at four measurement locations. Species and temperature measurements will be made optically using a fiber optic cable to carry light between the measurement location and the instrument. Contact: Joel Silver.
Optical Coherence Tomography
Optical coherence tomography (OCT) is a rapidly developing optical imaging method that uses light to obtain images with high resolution (10 - 100 times greater than ultrasound) to depths of 1-3 mm in biological tissues and other materials. Applications include research in biology and medicine and imaging of diseased tissues in situ.
Examples of images obtained with spectral domain OCT at different center wavelengths and resolution. (a) atherosclerotic plaque (b) developing otic structures in an X.lavis tadpole (c) cellular structure in onion.
OCT SYSTEM FEATURES
- Ultra-broadband light source
- Tunable center wavelength
- Adjustable resolution 10s to 1s of mm
- Simple, turnkey operation
A limiting factor of all Fourier domain OCT methods is the complex conjugate ambiguity due to Fourier transform of real-valued data; the image is symmetric with respect to the zero plane of the interferometer. Only half of the imaging depth range is useful in practice to avoid overlapping mirror images. Resolving the complex conjugate ambiguity doubles the available imaging depth range by allowing the interferometer zero plane to be within the sample. Modulating the phase of the OCT light source separates the real and imaginary components of the OCT return signal into components at the modulation frequency and at twice the modulation frequency. More about this approach is in this poster presented at SPIE Photonics West/Bios 2010: High-Speed Full-Range Imaging with Harmonic Detection Swept-Source Optical Coherence Tomography.
This animation shows successively deeper images of a tadpole's head (OCTmovie.gif endless loop, 4.7MB)
Contact Kris Peterson
Optical coherence tomography images of a wedge-shaped thermal barrier coating applied to a test part, taken at three different wavelengths. Longer wavelengths penetrate farther into the coating, showing the underlying interface of the coating with the substrate.
Under funding from the National Science Foundation and the Air Force, Southwest Sciences is investigating the application of optical coherence tomography (OCT) to detect defects in composite materials. For instance, if a thermal barrier coating on a gas turbine or aircraft engine part peels off, the underlying part may be exposed to heat stresses that can cause failure. OCT can be used to image the interface of the coating with the underlying part, improving estimates of the coating lifetime and helping to determine coating failure modes. Ultimately this will help get the most use from these expensive components while controlling the risk of failure. Contact Kris Peterson
Semiconductor Process Gas Purity
Advanced semiconductor manufacturing methods demand exceptionally pure gases. Under Department of Commerce funding, we have developed a near-IR diode laser-based system for measuring traces of moisture in high purity process gases. A combination of patented and patent-pending methods was used to achieve a very dry detection sensitivity of 65 parts-per-trillion for water in air, as determined in tests using the Low Frost Point Generator at NIST. Moisture in corrosive gases can be detected as well; tests were conducted on moisture in hydrogen chloride (HCl).
The combination of technical and commercial success achieved in this SBIR-funded project led to Southwest Sciences' nomination by NIST for the Tibbetts Award. This award, named in honor of the founder of the SBIR program, is an initiative of the U.S. Small Business Administration "to recognize the technological innovation, economic impact and business achievements of those variously involved in the federal Small Business Innovation Research (SBIR) Program." Want more information about the Tibbetts Award? For more information about Southwest Sciences moisture monitoring system, contact: Chris Hovde or Joel Silver
Low-Cost VCSEL-Based Sensors
Under contracts from the Air Force Phillips Laboratory (Lasers and Imaging Directorate) and DOE, Southwest Sciences developed a new generation of diode laser-based sensors using vertical cavity surface emitting lasers (VCSELs). This research led to a substantially reduced cost of diode laser-based instruments, by using new inexpensive laser and electronics designs, in order to open a broader range of potential gas sensing markets for diode laser-based instruments. These improvements were incorporated into the '46 Hawk hand-held methane leak sensors. Contact: Alan Stanton or Mark Paige
In Situ Monitoring of Plasma Etching
With support from DARPA, we have utilized a lead salt diode laser system
to conduct in situ measurements of reactive intermediates and etch
product gases in fluorocarbon-based etching of silicon and silicon dioxide.
The measured parameters include CF, CF2, and CF2O species
concentrations as well as gas temperature. This work has been conducted in
collaboration with the University
of New Mexico. Contact:Alan
Backscatter Gas Imaging
Soutwest Sciences is developing techniques to image gas leaks using active laser spectroscopy and a micro-mirror array. A low power beam of spatially-moduated laser light (designed to be eye-safe) is transmitted, and the return light is demodulated to produce an image of the gas concentration, enabling steam leak detection at nulcear power plants and other high-value facilities. Contact: Chris Hovde
Perimeter Monitors for Hazardous Gases
Southwest Sciences received funding from a consortium of oil companies under the Petroleum Environmental Research Forum for the development and testing of prototype diode laser-based instrumentation for perimeter monitoring of hazardous gases (e.g. hydrogen fluoride or hydrogen sulfide) in refineries or chemical plants. We delivered a prototype HF monitor to PERF which was field-tested at a refinery in the Northeastern United States during the particularly cold and snowy winter of 1994 - 1995. The instrument performed flawlessly while it was continuously operated outdoors over a period of several months. Contact: Alan Stanton
Southwest Sciences is working with the research group of Professor Budker at Berkeley to develop nonlinear magneto-optical rotation with amplitude or frequency modulated light (AM- and FM-NMOR) and related methods for the practical measurement of magnetic fields. A modulated diode laser beam creates an atomic alignment in a gas of alkali atoms. The alignment rotates the polarization of probe laser, which is detected in a balanced polarimeter. The amount of polarization rotation shows a sharp resonance when the modulation frequency is a harmonic of the Larmor frequency. The sensitivity achieved in the lab can approach 1 fT (1e-15 T), whereas Earth's field is about 50 000 nT (5e-5 T) so very high precision is possible. Potential applications include magnetometry in the laboratory and in space, medical diagnostics, and magnetic anomaly detection. contact: Chris Hovde
Imaging Magnetic Fields
Together with the research groups of Professors Budker and Hemmer, Southwest Sciences is working to develop techniques for measuring spatially resolved magnetic fields using NV-doped diamonds. The goal is to develop a "magnetic microscope" that can image fields from small samples with high spatial resolution and magnetic sensitivity. Applications include biology and materials science. Contact: Chris Hovde
LABORATORY SPECTROSCOPY AND TECHNIQUE DEVELOPMENT
We have utilized near-infrared diode lasers operating at wavelengths between 630 and 2650 nm to measure a wide variety of gas phase species by absorption spectroscopy, including oxygen, nitrous oxide, hydrogen chloride, hydrogen fluoride, water vapor, methane, ammonia, hydrogen cyanide, carbon dioxide, carbon monoxide, hydrogen sulfide, hydrogen peroxide, acetylene, and nitric oxide. We have also measured gas phase radical species, including the hydroxyl (OH), formyl (HCO), and hydroperoxyl (HO2) radicals, as well as a molecular ion (N2+). Some current or recently completed projects include:
Detection of Ammonia and Nitric Oxide Using Antimonide Diode Lasers
We have used recently developed antimonide diode lasers operating to measure nitric oxide (NO) in the 2650 nm region and ammonia (NH3) in the 2220 nm region. Applications include continuous emissions monitoring and atmospheric flux measurements. The results of this work indicate that NO can be detected at sub part-per-million levels and NH3 can be detected at single digit part per billion levels. Care must be used to avoid interfering lines from water and other gases. This work is supported by the Environmental Protection Agency and by the National Oceanic and Atmospheric Administration. Contact: Alan Stanton or Chris Hovde.
Wavelength Modulation Detection of the Hydroxyl Radical Using a Diode Laser with Sum Frequency Mixing
We generated greater than 1.5 microwatts of tunable wavelength modulated 308 nm radiation by sum-frequency mixing the outputs of a 90 mW 835 nm diode laser and a 1.5 W argon ion laser. The 308 nm light source was used to measure hydroxyl radicals, formed in a discharge flow reactor, by direct absorption, wavelength modulation absorption spectroscopy, and laser-induced fluorescence. The results of this work may facilitate quantitative measurements of the OH radical in the troposphere. This work was funded by the National Science Foundation. Contact: Kris Peterson.
Diode Laser Absorption
With support from a broad range of Federal agencies, especially the National Science Foundation, the Department of Energy, and NASA, Southwest Sciences has developed and optimized the technique of high frequency wavelength modulation spectroscopy (WMS) for sensitive absorption measurements using diode lasers. Using this technique, we have demonstrated an absorption detection sensitivity equivalent to measuring a change of one part in one ten-millionth of the laser intensity. This high sensitivity provides a capability for measurement of very small trace gas concentrations (sub-ppm or even sub-ppb). We have also developed techniques for minimizing unwanted optical interference effects and for stabilizing the laser wavelength while minimizing low frequency baseline drift. Currently we are studying new multiple pass optical designs and new digital signal processing methods. Contact: Chris Hovde, Joel Silver, or Alan Stanton