Analysis of probe volume effects associated with laser-saturated fluorescence measurements

Abstract

Time-dependent and steady-state lateral fluorescence intensities are obtained analytically as a function of the saturation parameter along the laser axis for Gaussian and quasi-Lorentzian irradiance profiles. The sensitivity of these fluorescence intensities to quenching is compared with the sensitivity of the center-line fluorescence emission. Experimental saturation curves are analyzed similarly and compared to the steady-state predictions. The results show that the desired insensitivity of laser-saturated fluorescence (LSF) measurements to quenching is adversely affected by the fractional laser power in the wings of the transverse irradiance distribution. Ambiguities in the analysis of LSF measurements arising from these effects can be essentially eliminated by conducting the analysis with respect to the center-line fluorescence emission as opposed to the fluorescence intensity.