Dependence of laser-induced fluorescence on exciting-laser power: partial saturation and laser – plasma interaction^*

Masaryk University, Faculty of Science, 61137 Brno, Czech Republic

^a e-mail: pdvorak@physics.muni.cz

Received: 15 January 2015
Revised: 20 May 2015
Accepted: 1 July 2015
Published online: 31 July 2015

Abstract

In recent publications on laser-induced fluorescence (LIF), the measurements are usually constricted to the region of weak exciting-laser power – the so called linear LIF. In this work, a practical formula describing the dependence of partially saturated fluorescence on the exciting-laser power is derived, together with practical implementation suggestions and comments on its limitations. In the conclusion, the practical formula$$F\left(E_L\right)=\frac{\alpha E_L}{1+\beta E_L}$$ is proposed with the limitation for validity β E_L ≤ 0.4, where α E_L is the hypothetical linear fluorescence without saturation effects, and a more general formula is derived, which is valid for higher values of α E_L as well. Extending the range of exciting laser power to the region of partial saturation enhances the signal-to-noise ratio. Such measurements in a surface dielectric barrier discharge further reveal discharge disruption by photoelectrons emitted from the dielectric surface. Methods of control and solution of this problem are discussed.