Reviewed by Danielle Ellis, B.Sc.Sep 4 2024
In a new study that was published in Light: Science & Applications, femtosecond laser sheet-compressed ultrafast photography (fsLS-CUP) is presented by Dr. Yogeshwar Nath Mishra, Dr. Peng Wang, Dr. Murthy S. Gudipati, and Professor Lihong V. Wang from the California Institute of Technology. Dr. Bauer and Dr. Meyer collaborated on this study.
The fsLS-CUP system captures ultrafast image sequences of three major types of laser-induced signals in flame. The femtosecond (fs) laser sheet excites PAHs and soot nanoparticles in the soot inception region of a hydrocarbon flames. The ultrafast camera captures the movies of laser-induced fluorescence (from PAH molecules), scattering and incandescence signals (from soot nanoparticles) with the frame interval from sub-nanosecond down to tens of picoseconds. Only three representative frames are shown here for simplicity. Full movies can be found online accompanying the published paper. Image Credit: Yogeshwar Nath Mishra, Peng Wang, Florian J. Bauer, Murthy S. Gudipati, and Lihong V. Wang
Polycyclic aromatic hydrocarbons (PAHs), the precursors of soot produced by candle flames and airplane engines, are hazardous to both people and the environment. These carbon-based particles are becoming useful for use in electrical devices and renewable energy. They are also ubiquitous in space, accounting for 10–12% of interstellar matter.
However, the fingerprint signals of soot and PAHs have extremely limited lifetimes in flames, lasting just a few billionths to millionths of a second. This short life necessitates the use of extremely rapid cameras to capture their space and temporal activities.
Currently, existing imaging systems can only record a few million frames per second and frequently require numerous laser pulses, resulting in undesirable heating issues.
Image Credit: Kobee/Shutterstock.com
Traditional technologies are similarly constrained in that they can only capture repeating occurrences by progressively capturing numerous images and stitching them together to form a complete motion picture. These limits have left combustion scientists anxiously anticipating a new technique to overcome these obstacles.
This innovative approach, as the world’s fastest single-shot planar imaging camera, captures entire films of femtosecond laser-flame dynamics at an astonishing 250 billion frames per second (Gfps), which is 20,000 times faster than previous imaging systems.
fsLS-CUP uses a single femtosecond laser pulse to image laser-induced fluorescence (LIF) from PAHs, laser-induced heating (LIH) from soot particles, and elastic light scattering (ELS) from laser-soot interactions in real time over a large field.
Scientists have used ultrafast laser pulses to capture rapid 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, that can capture some extremely fast phenomena in nature.
Dr. Yogeshwar Nath Mishra, Department of Electrical Engineering, California Institute of Technology
Dr Mishra added, “Ultimately, it has not only advanced our understanding of hydrocarbon and nanoparticle formation and growth in flames but also holds potential across multiple fields, making it a significant 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 science.”
Dr. Peng Wang noted that their study represents a big step forward in ultrafast imaging and research, with the potential to reveal quick events important to natural science and industry. The team continues to push the frontiers of imaging performance, such as speed, spatial resolution, and image reconstruction fidelity.
They successfully used real-time imaging to detect laser-induced signals from soot and PAHs in combustion. Wang thinks that further creativity and collaboration will result in additional discoveries and understanding in this subject. Overall, fsLS-CUP provides new opportunities for investigating transient phenomena in a planar arrangement.
Dr. Florian Bauer said that the fsLS-CUP approach uses compressed sensing to gather data in a single shot using only one femtosecond laser pulse. The approach has a large field of view. It can resolve both spatial and temporal features, making it suitable for studying diverse femtosecond laser-induced signals in PAHs and carbon nanoparticles.
It has effectively recovered critical information, such as the two-dimensional distribution of fluorescence lifetimes of PAH molecules. The approach also shows that femtosecond laser pulses can trigger incandescence in soot particles.
PAHs are robust molecules in interstellar space. Understanding the formation of PAHs and carbon soot expands our knowledge about their existence under astrophysical conditions as well.
Dr. Murthy S. Gudipati, Senior Research Scientist, Jet Propulsion Laboratory, California Institute of Technology
“Our study is relevant to PAH formation in hot environments, such as carbon-rich asymptotic giant branch stars. These evolved stars have hot atmospheres and strong stellar winds, creating ideal conditions for PAH formation. Additionally, the hot, expanding ejecta of supernova explosions provide another environment where PAHs could potentially form at high temperatures,” Dr Gudipati concluded.
Journal Reference:
Mishra, Y. N., et. al. (2024) Single-pulse ultrafast real-time simultaneous planar imaging of femtosecond laser-nanoparticle dynamics in flames. Light: Science & Applications. doi.org/10.1038/s41377-024-01588-x