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.
- LABORATORY SPECTROSCOPY
- ATMOSPHERIC AND ENVIRONMENTAL SCIENCES
- COMBUSTION SCIENCE
- SEMICONDUCTOR PROCESSING
- IMAGING
- INSTRUMENTATION DEVELOPMENT
- DEVELOPMENT OF MEASUREMENT TECHNIQUES
1. LABORATORY SPECTROSCOPY
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.
New Infrared Light Sources for Spectroscopy and Gas Sensing Applications
2. ATMOSPHERIC AND ENVIRONMENTAL SCIENCES
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: Chris Hovde(flux).
3. COMBUSTION SCIENCE
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 or Dan Kane
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: Dan Kane, 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. This project is conducted in collaboration
with Prof. Mark Linne of the
Colorado School of Mines. Contact: Dan
Kane
4. SEMICONDUCTOR PROCESSING
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
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 Prof. Harold Anderson of The University
of New Mexico. Contact: Dan
Kane or Alan
Stanton.
5. IMAGING
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. OCT also has potential for non-destructive testing
of specialized materials such as thermal barrier coatings used on jet engine
turbines.
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
