Two-photon excitation laser-induced fluorescence of carbon monoxide suffers from interference from mainly C<sub>2</sub> and strong pressure quenching. This paper presents an investigation of three excitation/detection schemes for two-photon excitation laser-induced fluorescence on carbon monoxide. The schemes are evaluated for pressure and quenching partner dependencies and C<sub>2</sub> interference. Three different emission bands lie in the Hopefield-Birge system: The Ångström B<sup>1</sup>Σ<sup>+</sup>→A<sup>1</sup>Π<sub>u</sub> band, with two-photon excitation through B<sup>1</sup>Σ<sup>+</sup>←X<sup>1</sup>Π around 230 nm; the Herzberg band C<sup>1</sup>Σ<sup>+</sup>→A<sup>1</sup>Π<sub>u</sub>, with two-photon excitation through, C<sup>1</sup>Σ<sup>+</sup>←X<sup>1</sup>Π, around 217 nm; and the third positive group b<sup>3</sup>Σ→a<sup>3</sup>Π, also with excitation of B<sup>1</sup>Σ<sup>+</sup>←X<sup>1</sup>Π around 230 nm. The measurements are performed in laminar premixed flames with various equivalence ratios as well as in a high-pressure cell, where pressure and species concentrations are varied in order to investigate the fluorescence quenching dependence.
Joakim Rosell, Johan Sjöholm, Mattias Richter, and Marcus Aldén, "Comparison of Three Schemes of Two-Photon Laser-Induced Fluorescence for CO Detection in Flames," Appl. Spectrosc. 67, 314-320 (2013)