kHz-rate four-dimensional fluorescence tomography using an ultraviolet-tunable narrowband burst-mode optical parametric oscillator

Recent work on four-dimensional (4D) tomographic imaging of reacting and non-reacting flows has utilized fluorescence, incandescence, or scattering from flow tracers, particulates, or aerosols, typically at the harmonics of an Nd:YAG laser. This paper presents high-speed 4D, volumetric laser-induced fluorescence measurements using an ultraviolet-tunable narrowband laser source to reach electronic transitions of chemical species of interest, such as the hydroxyl radical (OH), which may exist at parts-per-million (ppm) levels. A custom injection-seeded optical parametric oscillator pumped by a high-speed burst-mode laser was used for volumetric excitation of OH fluorescence, which was then captured by a pair of quadscopes to record eight unique views simultaneously at 10 kHz using only two high-speed intensified cameras. Successful tomographic imaging using high-energy, tunable narrowband radiation from a high-speed laser source lays the foundation for spatiotemporal, multidimensional analyses of a wide range of reacting and non-reacting flows of practical interest.