Excitation Line Optimization for Krypton Tagging Velocimetry and Planar Laser-Induced Fluorescence in the 200-220 nm Range

摘要

Krypton tagging velocimetry (KTV) requires high signal-to-noise ratio (SNR) to observe high-speed boundary layers and flow structures. In order to optimize the choice of laser excitation line for use in KTV (212.556 nm, 214.769 nm, 216.667 nm), a theoretical and experimental investigation of excitation processes was undertaken. This paper presents a multi-path, two-photon excitation, cross-section calculation, using an assumed finite basis of states consisting of 4p, 5s, 6s, 7s, 5p, 6p, 4d, 5d, and 6d orbitals. From the relative magnitudes of two-photon cross-sections for five Krypton lines, an excitation spectrum is constructed and compared against excitation spectrum data, with encouraging results. From this work and the successful comparison to experiment from our lab and those in the literature, we conclude that the optimal line is 212.556 nm for Kr-PLIF and single-laser KTV. For KTV where the read step in performed with a continuous wave (CW) laser diode, the 216.667 nm write-laser excitation is optimal.