Femtosecond Diffraction &
Imaging Science Lab

2020-11-24 145

Sometimes, a momentary freeze-frame from a video featuring an actor wearing such an alluring smile may do his countenance injustice, producing a hilariously ridiculous and unflattering shot. As such, observing a certain phenomenon on an extremely short time scale could reveal something that would otherwise escape our attention.


The Femtosecond Diffraction & Imaging Science Laboratory led by professor Song, Changyong at the Department of Physics, POSTECH, probes the phase transitions of matter in extremely short intervals of time, such as gold nanoparticles melting rapidly, with the help of the ‘PAL-XFEL’ installed at the Pohang Accelerator Laboratory located within POSTECH. The ‘PAL-XFEL’ produces light that is approximately one billion times brighter than the light used for chest X-ray examinations to capture images taking place on the femtosecond (one thousandth of a trillionth of a second) time scale in the molecular world.


One of the recent fascinating phenomena discovered by the Lab relates to ‘reverse phase transitions’. Normally, when the phase of matter goes from solid to liquid, its surface melts into a roundish shape, spreads out and then completely loses its original form. Observing the rapid melting of solid matter within an extremely short timeframe, however, demonstrated ‘reverse phase transitions’ through which solid matters revert to their initial shape before spreading out and melting. This is only observable with the PAL-XFEL, and most researchers who have become aware of these findings marvel at such never-before possible observations, to the extent of near disbelief.


Another research area of interest is to develop techniques to photograph the phenomena observed through the PAL-XFEL. The ‘single-pulse time-resolved imaging experimentation technique’ developed by the Lab allows for the consecutive capture of photos during the entire phase transition process. While conventional photograph technology required samples to be repeatedly manipulated and restored, the single-pulse technique simultaneously manipulates tens of thousands of samples prepared under the same conditions and then selects only the necessary photos. Since the technique eliminates the need to restore samples, researchers are relieved of the burden of limiting the intensity of manipulations and the shortcoming of having to accept the samples that are not restored to their exact original state.


The motto of the Femtosecond Diffraction & Imaging Science Laboratory, ‘We should take the initiative to discover our unique capacity and forge ahead in pioneering its application’, reflects the Lab’s research endeavors to encounter entirely new phenomena in the molecular world. This drives researchers to follow in the footsteps of countless scientists throughout history who labored tirelessly in their specific field and consequently made great achievements without any special regard to the responses of others. As the Lab encourages members to respect one another and build a sense of solidarity, this makes the place feel like a casual and comfortable café where members feel at ease to be themselves and engage in candid dialogue.