Abstract

In this work, laser absorption imaging is expanded in temporal resolution capability to kilohertz measurement rates by coupling sparsely sampled wavelength scanning and digital image postprocessing for diffraction correction. The setup employs an interband cascade laser near 3.34 μm to backlight an unsteady flame for species-specific 2D imaging of ethane (${\mathrm{C}}_2{\mathrm{H}}_6$) with a high-speed infrared camera. Injection-current laser tuning is achieved with a high-duty-cycle square wave that involves a sparse number of data samples per scan to recover an integrated absorbance area for the target ethane feature, thereby minimizing the number of camera frames needed. In conjunction, an image-by-image computational diffraction pattern removal scheme is employed based on inverse Fourier transformations with the aim to reject high spatial frequencies associated with diffraction while preserving spatial resolution of the flow field, without averaging in time. These methods are applied to achieve species-specific 2D cinematography of ethane absorption in an unsteady partially premixed flame with a spatial resolution of $\sim 415\mathrm{\mu m}$ and a temporal resolution of 2 kHz.

© 2019 Optical Society of America

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