Saturation effects in gas-phase degenerate four-wave mixing spectroscopy: nonperturbative calculations

Journal Article · Wed Sep 01 04:00:00 EDT 1993 · Journal of the Optical Society of America, Part B: Optical Physics; (United States)

DOI:https://doi.org/10.1364/JOSAB.10.001508· OSTI ID:5935274

Lucht, R P; Farrow, R L; Rakestraw, D J ^[1]

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1. Combustion Research Facility, Sandia National Laboratories, Livermore, California 94551 (United States)

Saturation effects in gas-phase degenerate four-wave mixing (DFWM) are investigated for conditions of interest for diagnostic applications in flames and plasmas. In particular, the case in which Doppler and collisional broadening are comparable, as is often the case for flame species such as NO and OH, is investigated. DFWM line shapes and signal intensities are calculated nonperturbatively and compared with high-resolution laser measurements. In the nonperturbative calculations the time-dependent density-matrix equations for a two-level system interacting with three laser fields are integrated directly on a grid of spatial locations along the phase-matching axis. The electric-field amplitude for the DFWM signal is determined by multiplying the time-varying, laser-induced polarization at each grid point by the appropriate phase factor and then by summing over all grid points. The calculations are in excellent agreement with measurements of DFWM line shapes and signal intensities for NO in a buffer gas of He over a wide range of He pressure. Under saturation conditions the pressure dependence of the DFWM signal is reduced greatly compared with the unsaturated case. The signal level is still dependent on the ratio of pure dephasing to quenching collisions, even for saturation conditions. From the standpoint of minimal dependence on collisional processes it appears that operation with pump-laser intensities approximately equal to the saturation intensity is optimal. The dependence of the DFWM line shape and signal intensity on the ratio of probe to pump-laser intensity is also investigated.

• OSTI ID: 5935274
• Journal Information: Journal of the Optical Society of America, Part B: Optical Physics; (United States), Journal Name: Journal of the Optical Society of America, Part B: Optical Physics; (United States) Vol. 10:9; ISSN JOBPDE; ISSN 0740-3224
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400102* -- Chemical & Spectral Procedures
CHALCOGENIDES
DENSITY MATRIX
FLAMES
FREQUENCY MIXING
HYDROXYL RADICALS
LASER SPECTROSCOPY
LINE BROADENING
MATRICES
NITRIC OXIDE
NITROGEN COMPOUNDS
NITROGEN OXIDES
OXIDES
OXYGEN COMPOUNDS
PLASMA DIAGNOSTICS
POLARIZATION
PRESSURE DEPENDENCE
RADICALS
SATURATION
SPECTROSCOPY