Capture opaque super fast scenes

Image: Schematic diagram of a single shot ultra-fast terahertz photography system. Source: Roberto Morandotti (INRS)

A research team led by Professor Roberto Morandotti has achieved the first single ultra-fast terahertz (THz) photographic system. Published in Nature Communications, this important result will provide the spatial and temporal evolution of ultra-short dynamics at sub-picosecond resolution.

In other words, researchers will now be able to reveal physical laws that require imaging speeds that exceed the limits of electronic sensors by orders of magnitude.

Unlike the rapid development of ultrafast imaging at traditional optical wavelengths, single ultrafast imaging of terahertz radiation is still unexplored. This is mainly due to a severe lack of critical equipment in the terahertz frequency range, such as high-speed modulators and cameras, which are often indispensable for ultra-fast imaging.

Professor Roberto Morandotti said: "This work is a major achievement for our team. By taking advantage of the unique penetration capabilities of terahertz radiation, our system is able to capture ultra-fast events in optically opaque scenes that are not normally available at traditional optical frequencies."

"We have successfully unlocked a single ultra-fast imaging in terahertz mode. Thanks to our work, we can now shoot a film of irreversible superfast phenomena with an interframe time interval of less than 1 picosecond, "said Junliang Dong, lead author of the study.

Ultra-fast imaging using terahertz radiation

Single ultrafast photography has become a key technique to elucidate the complex laws behind various ultrafast phenomena in nature. Driven by ultrafast lasers, high-speed cameras, and recent advances in the field of computational imaging, a single ultrafast optical imaging has been able to capture two-dimensional (2D) transient scenes at over a trillion frames per second, fast enough to visualize pulses of light traveling through space at the speed of light.

However, the most advanced single ultrafast imaging technology requires the imaging target to be optically transparent. This limitation prevents these technologies from exploring many of the key ultrafast phenomena that occur in media with short optical penetration depths, such as the dynamics of laser ablation in ceramics, magnetization in iron films, and carrier excitation in semiconductors.

Recently, imaging using terahertz radiation has attracted great interest due to its ability to "penetrate" a variety of materials. However, single ultra-fast terahertz imaging is still in its infancy due to the lack of high-speed terahertz cameras.

In this study, Morandotti's team from the Materiaux Tele Communications Research Center in INRSEnergie performed terahertz detection using electro-optical sampling techniques using a carefully designed optical detection beam that multiplexed simultaneously in both the time and spatial frequency domains.

Professor Morandotti explains, "Because it relies only on common optical components such as beam splitters, optical delay lines, rasters, and CCD cameras, our technology essentially bypasses the need for any terahertz high-speed device. Even so, it is powerful enough to record ultra-fast scenes carried by terahertz waves in a single shot." .

These transient events occur in two-dimensional space and on femtosecond to picosecond time scales, and real-time imaging reflects a variety of fundamental mechanisms that are still complex and mostly unavailable, such as chemical reactions and light interactions with matter.

According to the researchers, their system is envisioned as an unprecedented tool for studying non-repeatable or destructive dynamics in advanced materials and structures, such as 2D materials, or even biological materials that are usually optically opaque, such as skin and corneas.

Junliang Dong et al, Single-shot ultrafast terahertz photography, Nature Communications (2023). DOI: 10.1038/s41467-023-37285-3

Source:Institut national de la recherche scientifique - INRS