Scientists from the Faculty of Pure and Applied Sciences at The University of Tsukuba created scanning tunneling microscopy (STM) "snapshots" with a delay between frames much shorter than previously possible. By using ultrafast laser methods, they improved the time resolution from picoseconds to tens of femtoseconds, which may greatly enhance the ability of condensed matter scientists to study extremely rapid processes.
One picosecond, which is a mere trillionth of a second, is much shorter than the blink of an eye. For most applications, a movie camera that could record frames in a picosecond would be much faster than necessary. However, for scientists trying to understand the ultrafast dynamics of materials using STM, such as the rearrangement of atoms during a phase transition or the brief excitation of electrons, it can be painfully slow.
Now, a team of researchers at the University of Tsukuba designed an STM system based on a pump-probe method that can be used over a wide range of delay times as short as 30 femtoseconds. In this technique, a "pump" laser is used to excite the material, followed quickly by a "probe" laser. The delay time is controlled by movable mirrors that change the distance the probe beam has to travel. At the speed of light, this translates into delay times on the order of femtoseconds. This timescale is needed to get a more complete understanding of the behavior of materials. "In condensed matter, dynamics are often not spatially uniform, but rather are strongly affected by local structures such as atomic-level defects, which can change over very short timescales," senior author Professor Hidemi Shigekawa says.
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