World’s fastest single-shot 2D imaging technique captures ultra-fast flame dynamics

Candle flames and aircraft engines produce tiny soot particles from polycyclic aromatic hydrocarbons (PAHs) as precursors, both of which are harmful to humans and the environment. These carbon-based particles are also common in space, making up 10–12% of interstellar matter, and are becoming valuable for electronics and sustainable energy. However, the fingerprint signals of soot and PAHs have very short lifetimes in flames, lasting only a few billionths to millionths of a second. This brief existence requires very fast cameras to capture their behavior in both space and time.

Currently available imaging systems can only capture a few million frames per second and often require multiple laser pulses, leading to unwanted heating issues. Traditional methods are also limited because they can only capture repetitive events by sequentially recording multiple frames to assemble a complete moving image. These constraints have led combustion science researchers to eagerly await a new tool to overcome these challenges.

In a new article published in Light: science and applicationsDr. Yogeshwar Nath Mishra, Dr. Peng Wang, Dr. Murthy S. Gudipati, and Professor Lihong V. Wang from the California Institute of Technology, in collaboration with Dr. Florian J. Bauer from the Friedrich-Alexander University of Erlangen, present femtosecond laser sheet compression ultrafast photography (fsLS-CUP). This revolutionary technique, as the world’s fastest single-shot planar imaging camera, captures full-length movies of femtosecond laser flame dynamics at an unprecedented 250 billion frames per second (Gfps), making it 20,000 times faster than existing imaging systems.

Using a single femtosecond laser pulse, the fsLS-CUP enables simultaneous, wide-field, real-time imaging of laser-induced fluorescence (LIF) of PAHs and laser-induced heating (LIH) of soot particles, as well as elastic light scattering (ELS) of laser-soot interactions.

Dr Yogeshwar Nath Mishra explained, “Scientists have used ultrafast laser pulses to capture fast chemical reactions and laser interactions with materials in real time. Using a femtosecond laser and a streak camera, we have developed a new 2D imaging method, fsLS-CUP, which can capture some extremely fast phenomena in nature.

“Ultimately, this technique not only advances our understanding of how hydrocarbons and nanoparticles form and grow in flames, but also holds potential in many areas, making it an important milestone in ultrafast imaging technology. Our research, which includes the fastest observation of PAHs, complements NASA’s mission to explore the origins of life and cosmic evolution. Beyond combustion research, this technique has broad applications in physics, chemistry, biology, medicine, energy and environmental sciences.”

Dr. Peng Wang emphasized that their work represents a significant advancement in the field of ultrafast imaging and science, with the potential to reveal rapid phenomena critical to natural science and technology. The team continues to push the boundaries of imaging performance, particularly in terms of speed, spatial resolution, and image reconstruction fidelity.

They successfully applied real-time imaging to observe laser-induced signals from soot and PAHs during combustion. Wang believes that ongoing innovation and collaboration will lead to new discoveries and better understanding in this field. Overall, fsLS-CUP opens new possibilities for studying transient phenomena in a planar configuration.

Dr. Florian Bauer highlighted that the fsLS-CUP technique allows for single-shot data acquisition using a single femtosecond laser pulse, exploiting compressed sensing. The method offers a wide field of view and resolves spatial and temporal details, making it suitable for observing various femtosecond laser-induced signals in PAHs and carbon nanoparticles. It successfully extracted crucial details such as the 2D distribution of fluorescence lifetimes of PAH molecules. The technique also confirmed that femtosecond laser pulses can induce incandescence in soot particles.

Dr Murthy S. Gudipati, an expert on PAH astrochemistry, said, “PAHs are robust molecules in interstellar space. Understanding the formation of PAHs and carbon soot also expands our knowledge about their existence in astrophysical conditions.

“Our study is relevant to the formation of PAHs in hot environments, such as carbon-rich asymptotic giant stars. These evolved stars have hot atmospheres and strong stellar winds, creating ideal conditions for PAH formation. In addition, hot, expanding ejecta from supernova explosions provide another environment where PAHs could potentially form at high temperatures.”