Short, femtosecond (10-15 s) pulses of intense laser light offer the fastest ways to manipulate material properties. One active area of research is to investigate how such pulses can be used to trigger ultrafast phase transitions, which results in colossal changes in a material’s properties on very short timescales. During these phase transitions the structure of the material can evolve extremely rapidly so that conventional probes of the crystal structure, such as X-ray and electron diffraction, produce blurred images, and the transition pathway cannot be resolved. Although optical pulses have the required temporal resolution, their wavelength is too long to measure the atomic positions directly. To overcome this limitation, researchers at the Fritz Haber Institute instead used an optical technique to measure the forces that dictate the atomic positions, thus enabling an ultrafast optical probe of the crystal structure.
The technique was used to measure the structural component of the photoinduced insulator-metal phase transition in VO2, using samples grown and characterized at the University of Vanderbilt. When the laser strikes the material, vibrations, which are characteristic of the insulating phase, are created. By using a high power laser, these vibrations could be completely eliminated, providing insights into the nature of the timescale and driving mechanism of the phase transition. These findings have been published in Nature Communications. (Read more in German).
(Nat. Commun., 3, 721 (2012), doi: 10.1038/ncomms1719)
Contact person: Dr Simon Wall (firstname.lastname@example.org)