Extension of wavelength-modulation spectroscopy to large modulation depth for diode laser absorption measurements in high-pressure gases
- 10 February 2006
- journal article
- Published by Optica Publishing Group in Applied Optics
- Vol. 45 (5), 1052-1061
- https://doi.org/10.1364/ao.45.001052
Abstract
Tunable diode laser absorption measurements at high pressures by use of wavelength-modulation spectroscopy (WMS) require large modulation depths for optimum detection of molecular absorption spectra blended by collisional broadening or dense spacing of the rovibrational transitions. Diode lasers have a large and nonlinear intensity modulation when the wavelength is modulated over a large range by injection-current tuning. In addition to this intensity modulation, other laser performance parameters are measured, including the phase shift between the frequency modulation and the intensity modulation. Following published theory, these parameters are incorporated into an improved model of the WMS signal. The influence of these nonideal laser effects is investigated by means of wavelength-scanned WMS measurements as a function of bath gas pressure on rovibrational transitions of water vapor near . Lock-in detection of the magnitude of the signal is performed to remove the dependence on detection phase. We find good agreement between measurements and the improved model developed for the component of the WMS signal. The effects of the nonideal performance parameters of commercial diode lasers are especially important away from the line center of discrete spectra, and these contributions become more pronounced for signals with the large modulation depths needed for WMS at elevated pressures.
Keywords
This publication has 26 references indexed in Scilit:
- Development of a sensor for temperature and water concentration in combustion gases using a single tunable diode laserMeasurement Science and Technology, 2003
- Simultaneous in situ measurement of CO, H _ 2 O, and gas temperatures in a full-sized coal-fired power plant by near-infrared diode lasersApplied Optics, 2003
- In situ combustion measurements of CO with diode-laser absorption near 23 µmApplied Optics, 2000
- Development of an automated diode-laser-based multicomponent gas sensorApplied Optics, 2000
- Diode-laser sensor for monitoring multiple combustion parameters in pulse detonation enginesProceedings of the Combustion Institute, 2000
- Diode laser measurements of concentration and temperature in microgravity combustionMeasurement Science and Technology, 1999
- Diode laser absorption sensors for gas-dynamic and combustion flowsMeasurement Science and Technology, 1998
- Frequency modulation and wavelength modulation spectroscopies: comparison of experimental methods using a lead-salt diode laserApplied Optics, 1992
- Trace gas detection with short-external-cavity InGaAsP diode laser transmitter modules operating at 158 μmApplied Optics, 1988
- Atmospheric pressure monitoring of trace gases using tunable diode lasersApplied Optics, 1982