Single-pulse real-time billion-frames-per-second planar imaging of ultrafast nanoparticle-laser dynamics and temperature in flames

Abstract

Unburnt hydrocarbon flames produce soot, which is the second biggest contributor to global warming and harmful to human health. The state-of-the-art high-speed imaging techniques, developed to study non-repeatable turbulent flames, are limited to million-frames-per-second imaging rates, falling short in capturing the dynamics of critical species. Unfortunately, these techniques do not provide a complete picture of flame-laser interactions, important for understanding soot formation. Furthermore, thermal effects induced by multiple consecutive pulses modify the optical properties of soot nanoparticles, thus making single-pulse imaging essential. Here, we report single-shot laser-sheet compressed ultrafast photography (LS-CUP) for billion-frames-per-second planar imaging of flame-laser dynamics. We observed laser-induced incandescence, elastic light scattering, and fluorescence of soot precursors - polycyclic aromatic hydrocarbons (PAHs) in real-time using a single nanosecond laser pulse. The spatiotemporal maps of the PAHs emission, soot temperature, primary nanoparticle size, soot aggregate size, and the number of monomers, present strong experimental evidence in support of the theory and modeling of soot inception and growth mechanism in flames. LS-CUP represents a generic and indispensable tool that combines a portfolio of ultrafast combustion diagnostic techniques, covering the entire lifecycle of soot nanoparticles, for probing extremely short-lived (picoseconds to nanoseconds) species in the spatiotemporal domain in non-repeatable turbulent environments. Finally, LS-CUP’s unparalleled capability of ultrafast wide-field temperature imaging in real-time is envisioned to unravel mysteries in modern physics such as hot plasma, sonoluminescence, and nuclear fusion.

Tutorial on compressed ultrafast photography

“… 57 This calibration can also reduce aberrations and field curvature. 123 In practice, the FOV and the maximum shearing distance are also limited to ensure high quality in captured images.…”

“…Besides background subtraction and white-field correction, threshold selection and edge detection are combined to optimize binarization 57 . This calibration can also reduce aberrations and field curvature 123 . In practice, the FOV and the maximum shearing distance are also limited to ensure high quality in captured images.…”

High-Channel Spectral-Temporal Active Recording (H-STAR) for Femtosecond Scenes Observation in a Single-Shot

“…Researchers have previously done a lot of work aiming at improvement of spatial resolution and achieved promising research results, such as space-and intensity-constrained compressed ultrafast photography (SIC-CUP), 15,16 stereo-polarimetric compressed ultrafast photography (SP-CUP), 17 and lossless-encoding compressed ultrafast photography (LLE-CUP). 18,19 However, in most of these studies, the amount of imaging channels performed is still limited. 20,21 Therefore, a newly designed compressed imaging optical system, which enables substantially increasing the imaging channels, is needed to achieve high-resolution reconstruction and a large frame number at the same time.…”

“…Ultrafast compressed imaging methods use a compressed imaging optical system to compress high-dimensional data into low-dimensional data for acquisition, and then reconstruct the high-dimensional time series images from the acquired low-dimensional observed images based on the CS. − However, since ultrafast compressed imaging methods need to sparsely encode the scene, some information in the original scene is discarded, leading to the decrease of the spatial resolutions. Researchers have previously done a lot of work aiming at improvement of spatial resolution and achieved promising research results, such as space- and intensity-constrained compressed ultrafast photography (SIC-CUP), , stereo-polarimetric compressed ultrafast photography (SP-CUP), and lossless-encoding compressed ultrafast photography (LLE-CUP). , However, in most of these studies, the amount of imaging channels performed is still limited. , Therefore, a newly designed compressed imaging optical system, which enables substantially increasing the imaging channels, is needed to achieve high-resolution reconstruction and a large frame number at the same time.…”

Simultaneous Inversion of Particle Size Distribution, Thermal Accommodation Coefficient, and Temperature of In-Flame Soot Aggregates Using Laser-Induced Incandescence

“…In terms of temporal resolution, time-resolved laser-induced incandescence (TiRe-LII) technology provides nanosecond temporal precision, enabling the deduction of particle size distribution based on the cooling rates of soot particles [ 18 , 19 ]. Significant innovations, such as single-shot laser-sheet compressed ultrafast photography (LS-CUP), have further pushed the boundaries of temporal resolution in planar LII imaging to the sub-nanosecond level [ 20 ]. Collectively, these advancements in LII technology deliver informative signals with spatial resolutions spanning from 0D to 3D, wavelengths covering two to the full spectra, and temporal resolutions extending from nanoseconds to sub-nanoseconds.…”