J. Walewski et al., Dependence of partially saturated polarization spectroscopy signals on pump intensity and collision rate - art. no. 063816, PHYS REV A, 6406(6), 2001, pp. 3816
Understanding the saturation behavior of polarization-spectroscopy signals
is a vital task for the development of this method as a versatile tool for
quantitative detection of trace species. Recent progress in the theoretical
treatment of the polarization-spectroscopy process offers the opportunity
of studying its saturation behavior thoroughly. This theoretical treatment,
referred to as direct numerical integration (DNI) calculations, is based o
n numerically demanding calculations; that is why we present a simple model
that describes the curve shape of polarization spectroscopy power-dependen
ce scans in both the saturated and the unsaturated regime. Polarization-spe
ctroscopy-saturation curves in the copropagating beam geometry from the exc
itation of OH A (2)Sigma (+)-X (2)Pi (0,0) at the Q(2)(8) line in a low-pre
ssure flame were compared to both results from the DNI calculations and to
our proposed analytical equation. Our simple model provides excellent fits
to polarization-spectroscopy-saturation curves for absorption lines dominat
ed by homogeneous broadening and for narrow-bandwidth excitation sources. T
he model does not give a good agreement with experiment for lines dominated
by inhomogeneous broadening. For this case an empirical equation is propos
ed and investigated. Our proposed model offers a starting point for a simpl
ification of the underlying polarization-spectroscopy theory, the complexit
y of which has been a major obstacle to the further development of this the
ory.