A research team led by Yunhua Yao from East China Normal University announced on Apr. 10 the development of a new imaging technique that captures detailed information about ultrafast processes at the microscopic level. The method, called compressed spectral-temporal coherent modulation femtosecond imaging (CST-CMFI), allows scientists to observe and analyze phenomena occurring in hundreds of femtoseconds with greater detail and speed than previously possible.
The ability to capture both brightness and internal structure in a single measurement is expected to advance understanding in fields such as physics, chemistry, biology, and materials science. "In the fields of physics, chemistry, biology and materials science, many important phenomena happen incredibly fast," said Yunhua Yao. "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 researchers published their findings in Optica, describing how CST-CMFI was used to observe real-time evolution of plasma generated by a femtosecond laser in water as well as carrier dynamics excited by laser light in ZnSe. The method combines time-spectrum mapping, compressive spectral imaging, and coherent modulation imaging—enabling collection of more data per sequence while capturing very fast changes.
According to Yao, "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." He added that it may also lead to better electronics or solar cells through improved understanding at fast timescales.
Historically single-shot ultrafast optical imaging has only captured changes in intensity; however phase characteristics are important for revealing how light interacts with matter. The team's approach uses chirped laser pulses so each wavelength encodes a different moment in time—information later reconstructed into an ultrafast movie using neural networks.
Yao said their demonstration showed phase variations associated with carrier dynamics even when intensity remained unchanged: "Using CST-CMFI, we were able to see phase variations associated with the carrier dynamics, even when there were no significant changes in intensity," he said. "This highlights a key advantage of our method: Phase measurements can be much more sensitive than intensity measurements in detecting subtle ultrafast processes." Next steps include expanding applications toward observing interface dynamics or phase transitions requiring sensitive detection.
