Extension of wavelength-modulation spectroscopy to large modulation depth for diode laser absorption measurements in high-pressure gases.

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 1388 nm. Lock-in detection of the magnitude of the 2f signal is performed to remove the dependence on detection phase. We find good agreement between measurements and the improved model developed for the 2f 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 2f signals with the large modulation depths needed for WMS at elevated pressures.

[1]  Joel A. Silver,et al.  Diode laser measurements of concentration and temperature in microgravity combustion , 1999 .

[2]  Ronald K. Hanson,et al.  Diode-laser sensor for monitoring multiple combustion parameters in pulse detonation engines , 2000 .

[3]  R. Hanson,et al.  In situ combustion measurements of CO with diode-laser absorption near 2.3 microm. , 2000, Applied optics.

[4]  O. Axner,et al.  Background Signals in Wavelength-Modulation Spectrometry by use of Frequency-Doubled Diode-Laser Light. II. Experiment. , 2001, Applied optics.

[5]  Takaya Iseki,et al.  A portable remote methane sensor using a tunable diode laser , 2000 .

[6]  D. Labrie,et al.  Second-harmonic detection with tunable diode lasers — Comparison of experiment and theory , 1981 .

[7]  R. Hanson,et al.  Selection of NIR H2O absorption transitions for in-cylinder measurement of temperature in IC engines , 2005 .

[8]  D. Cassidy,et al.  Trace gas detection with short-external-cavity InGaAsP diode laser transmitter modules operating at 1.58 microm. , 1988, Applied optics.

[9]  J. A. Silver,et al.  Frequency modulation and wavelength modulation spectroscopies: comparison of experimental methods using a lead-salt diode laser. , 1992, Applied optics.

[10]  Ronald K. Hanson,et al.  Development of a sensor for temperature and water concentration in combustion gases using a single tunable diode laser , 2003 .

[11]  Luc Thévenaz,et al.  Wavelength modulation spectroscopy: combined frequency and intensity laser modulation. , 2003, Applied optics.

[12]  Ronald K. Hanson,et al.  Wavelength modulation absorption spectroscopy with 2 f detection using multiplexed diode lasers for rapid temperature measurements in gaseous flows , 2004 .

[13]  T. Aizawa.  Diode-Laser Wavelength-Modulation Absorption Spectroscopy for Quantitative in situ Measurements of Temperature and OH Radical Concentration in Combustion Gases. , 2001, Applied optics.

[14]  F. Tittel,et al.  Development of an automated diode-laser-based multicomponent gas sensor. , 2000, Applied optics.

[15]  G. Wilson,et al.  Modulation Broadening of NMR and ESR Line Shapes , 1963 .

[16]  M. Allen,et al.  Diode laser absorption sensors for gas-dynamic and combustion flows. , 1998, Measurement science & technology.

[17]  O. Axner,et al.  Background signals in wavelength-modulation spectrometry with frequency-doubled diode-laser light. I. Theory. , 2001, Applied optics.

[18]  Luc Thévenaz,et al.  Experimental method based on wavelength-modulation spectroscopy for the characterization of semiconductor lasers under direct modulation. , 2004, Applied optics.

[19]  Volker Ebert,et al.  Digital, phase-sensitive detection for in situ diode-laser spectroscopy under rapidly changing transmission conditions , 2002 .

[20]  Laurence S. Rothman,et al.  The HITRAN molecular spectroscopic database: edition of 2000 including updates through 2001 , 2003 .

[21]  Jonathan T. C. Liu,et al.  Large-modulation-depth 2f spectroscopy with diode lasers for rapid temperature and species measurements in gases with blended and broadened spectra. , 2004, Applied optics.

[22]  J. Hodges,et al.  Wavelength-modulation laser hygrometer for ultrasensitive detection of water vapor in semiconductor gases. , 2001, Applied optics.

[23]  Daniel T. Cassidy,et al.  Atmospheric pressure monitoring of trace gases using tunable diode lasers. , 1982, Applied optics.

[24]  Ronald K. Hanson,et al.  Laser diode wavelength-modulation spectroscopy for simultaneous measurement of temperature, pressure, and velocity in shock-heated oxygen flows. , 1993, Applied optics.

[25]  O. Axner,et al.  Theoretical description based on Fourier analysis of wavelength-modulation spectrometry in terms of analytical and background signals. , 1999, Applied optics.

[26]  Volker Ebert,et al.  Simultaneous in situ measurement of CO, H2O, and gas temperatures in a full-sized coal-fired power plant by near-infrared diode lasers. , 2003, Applied optics.

[27]  Rolf Arndt,et al.  Analytical Line Shapes for Lorentzian Signals Broadened by Modulation , 1965 .