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Optical Multiplexing for Ultrafast Videography

Ek, Simon LU (2025)
Abstract
Capturing ultrafast phenomena requires imaging techniques capable of resolving events occurring on femtosecond time scales. Traditional high-speed cameras are limited by electronic readout speeds and cannot reach the terahertz (THz) frame rates necessary to observe processes such as laser filamentation, plasma formation, or light-matter interactions in general. To overcome these limitations, this thesis explores and advances Frequency Recognition Algorithm for Multiple Exposures (FRAME), an optical multiplexing technique that encodes multiple frames within a single exposure by using spatially modulated illumination pulses. These encoded frames are later separated computationally, enabling single-shot ultrafast videography.

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Capturing ultrafast phenomena requires imaging techniques capable of resolving events occurring on femtosecond time scales. Traditional high-speed cameras are limited by electronic readout speeds and cannot reach the terahertz (THz) frame rates necessary to observe processes such as laser filamentation, plasma formation, or light-matter interactions in general. To overcome these limitations, this thesis explores and advances Frequency Recognition Algorithm for Multiple Exposures (FRAME), an optical multiplexing technique that encodes multiple frames within a single exposure by using spatially modulated illumination pulses. These encoded frames are later separated computationally, enabling single-shot ultrafast videography.

A central achievement of this work is the first demonstration of phase-sensitive FRAME, which significantly enhances the technique’s ability to detect small refractive index variations. This was then extended to phase-sensitive ultrafast FRAME, allowing the visualization of laser filamentation in a single shot with high levels of detail. By leveraging FRAME’s ability to extract phase information directly from the recorded data, this work shows that it is possible to reconstruct highly detailed image sequences of plasma formation and filament propagation with FRAME.

This thesis also investigates the fundamental limitations and capabilities of FRAME, including its maximum achievable sequence depth, sensitivity, and resolution trade-offs. FRAME’s flexibility is highlighted through applications in diverse experimental configurations, from fluorescence-based multispectral imaging to high-speed shadowgraphy of fluid dynamics.

The results place FRAME within the broader historical context of imaging technology, illustrating how ultrafast optical multiplexing represents a paradigm shift in high-speed imaging. While challenges such as image quality and sensitivity remain, FRAME provides a versatile, easy-to-implement approach that pushes the limits of ultrafast videography. Future work should focus on refining the resulting image quality and improving ease of use, ultimately enabling FRAME’s adoption in broader scientific fields. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Dr. Liang, Jinyang, University of Quebec, Canada.
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Ultrafast Videography, Optical Multiplexing, Photonics, Structured Light, FRAME, Optical Diagnostics
pages
224 pages
publisher
Department of Physics, Lund University
defense location
Lecture Hall Rydbergsalen, Department of Physics, Professorsgatan 1, Faculty of Engineering LTH, Lund University, Lund. The dissertation will be live streamed, but part of the premises is to be excluded from the live stream.
defense date
2025-05-09 13:15:00
ISBN
978-91-8104-482-9
978-91-8104-481-2
language
English
LU publication?
yes
id
54a73878-3655-4d5e-bea8-fa536e37ee5a
date added to LUP
2025-04-10 12:54:45
date last changed
2025-04-14 09:48:28
@phdthesis{54a73878-3655-4d5e-bea8-fa536e37ee5a,
  abstract     = {{Capturing ultrafast phenomena requires imaging techniques capable of resolving events occurring on femtosecond time scales. Traditional high-speed cameras are limited by electronic readout speeds and cannot reach the terahertz (THz) frame rates necessary to observe processes such as laser filamentation, plasma formation, or light-matter interactions in general. To overcome these limitations, this thesis explores and advances Frequency Recognition Algorithm for Multiple Exposures (FRAME), an optical multiplexing technique that encodes multiple frames within a single exposure by using spatially modulated illumination pulses. These encoded frames are later separated computationally, enabling single-shot ultrafast videography.<br/><br/>A central achievement of this work is the first demonstration of phase-sensitive FRAME, which significantly enhances the technique’s ability to detect small refractive index variations. This was then extended to phase-sensitive ultrafast FRAME, allowing the visualization of laser filamentation in a single shot with high levels of detail. By leveraging FRAME’s ability to extract phase information directly from the recorded data, this work shows that it is possible to reconstruct highly detailed image sequences of plasma formation and filament propagation with FRAME.<br/><br/>This thesis also investigates the fundamental limitations and capabilities of FRAME, including its maximum achievable sequence depth, sensitivity, and resolution trade-offs. FRAME’s flexibility is highlighted through applications in diverse experimental configurations, from fluorescence-based multispectral imaging to high-speed shadowgraphy of fluid dynamics.<br/><br/>The results place FRAME within the broader historical context of imaging technology, illustrating how ultrafast optical multiplexing represents a paradigm shift in high-speed imaging. While challenges such as image quality and sensitivity remain, FRAME provides a versatile, easy-to-implement approach that pushes the limits of ultrafast videography. Future work should focus on refining the resulting image quality and improving ease of use, ultimately enabling FRAME’s adoption in broader scientific fields.}},
  author       = {{Ek, Simon}},
  isbn         = {{978-91-8104-482-9}},
  keywords     = {{Ultrafast Videography; Optical Multiplexing; Photonics; Structured Light; FRAME; Optical Diagnostics}},
  language     = {{eng}},
  publisher    = {{Department of Physics, Lund University}},
  school       = {{Lund University}},
  title        = {{Optical Multiplexing for Ultrafast Videography}},
  url          = {{https://lup.lub.lu.se/search/files/216830349/Avhandling_Simon_Ek_LUCRIS.pdf}},
  year         = {{2025}},
}