University of Tokyo researchers spaced frames logarithmically in time, letting 11 images span five orders of magnitude, from femtoseconds to nanoseconds, in a single measurement.
When a laser pulse strikes a material, a cascade of events follows. In the first femtoseconds, quadrillionths of a second, electrons absorb energy. Over picoseconds and nanoseconds, heat spreads, material melts or vaporizes, and shock waves form. Capturing all of that in a single recording has been a long-standing challenge for ultrafast imaging.
Researchers at the University of Tokyo have found a way to do it with relatively few frames. In a study published in Optica, they describe logarithmic ultrafast photography, in which frames are packed closely together at the start of an event and spaced farther apart as it unfolds.
“We wanted to find a way to connect these very different timescales in a single measurement,” said Keitaro Shimada, a postdoctoral researcher in the group of Keiichi Nakagawa and the study’s lead author. “In other words, we wanted to see both the first instance and what follows, without having to choose one or the other.”
The problem with evenly spaced frames
Most cameras, including high-speed and ultrafast ones, capture frames at regular intervals. That works well when events unfold at a steady pace. But many physical processes start extremely fast and then slow down. Evenly spaced frames force a trade-off: space them tightly and the recording ends before the later stages, or space them widely and the crucial early moments fall between frames.
A common workaround is to repeat an experiment many times, capturing each moment separately and stitching the results together. That works only if the event is perfectly reproducible, which many are not.
This technique, known as pump-probe measurement, has been the workhorse of ultrafast science for decades. One laser pulse triggers an event, and a second, delayed pulse probes it. By varying the delay across many repetitions, researchers build up a movie frame by frame. It is powerful, but each frame comes from a different run.
“We are particularly interested in phenomena that are difficult to reproduce exactly,” said Nakagawa, an associate professor in the university’s Department of Bioengineering. “In those cases, recording the early and later stages of the same event can reveal relationships that might be lost when a sequence is reconstructed from separate experiments.”
Frames on a logarithmic scale
The solution draws on a familiar idea from mathematics. On a logarithmic scale, each step represents a multiplication rather than an addition, so equal steps might correspond to 1, 10, 100 and 1,000 units. Logarithmic scales are used to describe phenomena that span huge ranges, such as earthquake magnitudes and sound levels.
Applying that idea to time means placing frames densely when changes happen quickly and sparsely when they slow down. Using the approach, the team captured key moments across five orders of magnitude in time, from femtoseconds to nanoseconds, with just 11 frames. Achieving the same coverage with evenly spaced frames would require far more images.
Light as a timekeeper
The technique builds on a method called sequentially timed all-optical mapping photography, or STAMP. Rather than using a mechanical shutter or electronic sensor that must reset between frames, STAMP uses an ultrashort laser pulse containing many wavelengths of light. Different wavelengths are delayed by different amounts, so each color arrives at the subject at a slightly different moment. Separating the colors afterward yields a series of images, each recording a different instant.
The new work adds a component the researchers call band-resolved individual delay generation, or BRIDGE. It extracts wavelength bands one after another and allows the delay of each band to be adjusted independently while preserving its specific moment in time. That flexibility lets the team set the timing of every frame, which is what makes logarithmic spacing possible.
The authors of the study are Shimada, Kohei Azuma, Jun Horiuchi, Dylan Thomas, Masato Ota and Nakagawa.
Potential applications
The researchers see uses in fields where fast events have long-lasting consequences. In laser processing, used in manufacturing to cut, drill and mark materials, understanding how the earliest interactions lead to later damage could help improve precision. Other potential applications include studies of material dynamics, plasma and shock-wave research and biomedical imaging.
Ultrafast imaging has become an increasingly powerful tool. The 2018 Nobel Prize in Physics recognized the development of techniques for generating ultrashort, high-intensity laser pulses, and the 2023 prize honored methods for producing attosecond pulses of light to study electrons. Logarithmic photography offers a complementary approach, focusing not on reaching ever-shorter timescales but on connecting short and long ones.
Limits
The technique captures a small number of frames, so it depends on choosing the right moments to record. For phenomena whose timing is not well understood in advance, researchers may need preliminary measurements to decide where to place the frames. STAMP-based methods also typically require that the subject interact with light in a way that can be imaged, which limits the kinds of samples they can study.
The work was supported by the Japan Science and Technology Agency and Japan’s Ministry of Education, Culture, Sports, Science and Technology. Its central idea is simple: when an event slows down over time, the camera can slow down with it.
Notes
- Shimada, K., Azuma, K., Horiuchi, J., Thomas, D., Ota, M., and Nakagawa, K. “Logarithmic ultrafast photography with band-resolved individual delay generation.” Optica, 25 September 2026. DOI: 10.1364/OPTICA.610944.
- University of Tokyo. “Quality over quantity in ultrafast photography.” EurekAlert!, 20 October 2026. https://www.eurekalert.org/news-releases/1148487.
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