Single-shot imaging captures more information about ultrafast microscopic processes than previously possible

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This visual illustration shows compressed spectral-temporal coherent modulation femtosecond imaging (CST-CMFI). A chirped laser pulse with time-varying spectral components illuminates a dynamic scene, enabling different wavelengths to capture successive temporal transients. By utilizing dispersion-encoded coherent modulation imaging, CST-CMFI retrieves both the intensity and phase evolutions. Credit: Yunhua Yao, East China Normal University

Researchers have developed a new imaging technique that captures more information about ultrafast processes in the microscopic world than was previously possible. The technique offers scientists a powerful new tool to observe and analyze a wide range of ultrafast phenomena—which can happen in hundreds of femtoseconds—with unprecedented detail and speed. Writing in Optica, the researchers describe their new ultrafast imaging technique, called compressed spectral-temporal coherent modulation femtosecond imaging (CST-CMFI).

"In the fields of physics, chemistry, biology and materials science, many important phenomena happen incredibly fast," said research team leader Yunhua Yao from East China Normal University. "Our new technique can capture the complete evolution of both the brightness and internal structure of an object in a single measurement. This is a big step forward for understanding the fundamental nature of matter, designing new materials and even uncovering the mysteries of biological processes."

The team used the new technique to observe ultrafast processes, including the real-time evolution of plasma generated by a femtosecond laser in water and carriers excited by a femtosecond laser in ZnSe.

"Beyond helping scientists study materials that change instantly in response to laser light, chemical reactions that rearrange atoms at lightning speed and the dynamic behavior of biomolecules over incredibly short timescales, CST-CMFI could help improve high-power laser technologies used for clean energy research, advanced manufacturing and scientific instrumentation," said Yao. "It might also lead to the development of more efficient electronics, improved solar cells and faster devices by enabling a better understanding of how materials behave at extremely fast timescales."

Researchers developed a new imaging technique called compressed spectral-temporal coherent modulation femtosecond imaging that simultaneously captures ultrafast changes in an object's intensity and its phase distribution in real-time. The imaging system is pictured. Credit: Yunhua Yao, East China Normal University

Capturing more information

The research is part of a larger effort at the Extreme Optical Imaging Laboratory at East China Normal University to develop ultrafast camera technologies, particularly those used for single-shot ultrafast optical imaging. These techniques capture incredibly fast events that cannot be repeated by using a single exposure, much like capturing a single frame of a movie.

Historically, single-shot ultrafast optical imaging could only capture changes in an object's brightness, or light intensity. However, the phase characteristics of light carry information on how light bends or changes speed as it passes through an object. In the new work, the researchers aimed to develop a method for capturing ultrafast changes in an object's intensity, along with its phase distribution, simultaneously and in real time.

To address this challenge, they combined time-spectrum mapping, compressive spectral imaging and coherent modulation imaging, allowing them to take advantage of each method's strengths: capturing very fast changes, collecting more data in a single sequence and recording detailed image information.

To do this, they used a chirped laser pulse, which contains various wavelengths of light that each arrive at slightly different times, allowing time to be encoded as wavelength. When this pulse interacts with an ultrafast event, the scattered light carries spatial, spectral and phase information, which is compressed into a single image using dispersion-encoded coherent modulation imaging.

A physics-informed neural network then reconstructs the data by separating the wavelengths and retrieving both intensity and phase at each moment. Because each wavelength corresponds to a different time, the reconstruction produces a sequence of frames that forms an ultrafast movie captured from a single exposure.

The researchers used the new technique to observe femtosecond laser–induced carrier dynamics in ZnSe. The images show the spatiotemporal evolution of the intensity (top images) and phase (bottom images). Notably, the phase variations are significantly more pronounced than the intensity fluctuations. Credit: Yunhua Yao, East China Normal University

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Observing ultra-fast phenomena

To demonstrate the effectiveness of their method, the researchers used it to observe two types of ultrafast phenomena. The first involved capturing the real-time evolution of plasma generated by a femtosecond laser in water. A better understanding of this process could be useful in laser surgery and medical procedures, for example. The results clearly showed both the intensity and phase changes within the plasma channel. The researchers observed the formation of a dense free-electron plasma in the focal region, which causes significant absorption and changes in the refractive index of the water.

They also used the method to study carrier dynamics in ZnSe to better understand how electrical charges behave inside the material after it is excited by light. This type of information is useful for designing better, faster and more efficient optical and electronic devices with this material.

"Using CST-CMFI, we were able to see phase variations associated with the carrier dynamics, even when there were no significant changes in intensity," said Yao. "This highlights a key advantage of our method: Phase measurements can be much more sensitive than intensity measurements in detecting subtle ultrafast processes."

Next, the researchers plan to expand the application range of the new method by using it to observe phenomena like interface dynamics and ultrafast phase transitions, both of which require detecting very small changes in the phase of light waves.

Currently, CST-CMFI converts spectral information into temporal information, making it unsuitable for ultrafast processes that are highly sensitive to spectral changes. To overcome this, the researchers aim to combine the principles of CST-CMFI with compressive ultrafast photography to develop an imaging method that resolves spectral and temporal information separately. They say this advancement will significantly broaden the practical utility and widespread applicability of the technology.

Publication details

Compressed Spectral-Temporal Coherent Modulation Femtosecond Imaging, Optica (2026). opg.optica.org/optica/abstract … 0.1364/OPTICA.587476

Journal information: Optica

Key concepts

Optics & lasersPlasma interactionsOptical techniques

Provided by Optica