Trace detection in gases using photoacoustic spectroscopy and Fabry-Perot interferometry

Thesis/Dissertation · Sun Jan 01 04:00:00 EST 1984

OSTI ID:6307560

Yip, B C.Y.

Two thermooptic-based detection systems for gases were developed and studied for their performances in monitoring air pollutants. In the first system which is based on the photoacoustic effect, a continuous-wave carbon dioxide laser was adapted for operation in the infrared with its output wavelength modulated between two consecutive vibration-rotation lines. This was accomplished by applying a time-varying electric field to a commercial piezoelectric pusher attached to the grating mount of the laser. Operating under wavelength modulation, the primary limitation on detectability in photoacoustic measurements - window absorption - was removed and the useful range for application was extended. This concept was illustrated by the determination of ppb levels of ethylene in nitrogen. The feasibility of using Fabry-Perot interferometry for in situ trace detection of gases was studied. The Fabry-Perot interferometric experiment was based on a single-beam geometry using modulated excitation and coherent detection of the signal. A laboratory built position stabilization circuit was employed to maintain the interferometer at its optimum point of operation. By combining this with wavelength modulation, the projected detection limit of the resulting scheme for C/sub 2/H/sub 4/ in nitrogen was found to be 20 ppb (S/N = 3).

• Research Organization: Johns Hopkins Univ., Baltimore, MD (USA). Dept. of Environmental Engineering Science
• DOE Contract Number: W-7405-ENG-82
• OSTI ID: 6307560
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400104* -- Spectral Procedures-- (-1987)
ALKENES
CARBON COMPOUNDS
CARBON DIOXIDE
CARBON OXIDES
CHALCOGENIDES
CHEMICAL ANALYSIS
DATA
ELEMENTS
ETHYLENE
EXPERIMENTAL DATA
FABRY-PEROT INTERFEROMETER
GAS LASERS
HELIUM-NEON LASERS
HYDROCARBONS
INFORMATION
INTERFEROMETERS
LASERS
MEASURING INSTRUMENTS
NITROGEN
NONMETALS
NUMERICAL DATA
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PHOTOACOUSTIC SPECTROSCOPY
QUANTITATIVE CHEMICAL ANALYSIS
SPECTROSCOPY
TRACE AMOUNTS