The need of sub-nanosecond resolution to reveal new features during laser induced solidification

This work reports the achievement of real-time optical reflectivity measurements with sub-nanosecond time resolution during pulsed laser induced structural transformations. The experimental set-up uses a streak camera and provides both, excellent time resolution in single exposure and high versatility. This is illustrated through the results obtained upon picosecond laser pulse melting of thin amorphous Ge films, which leads to processes that are completed in a time window of a few tens of nanoseconds. By means of a novel set-up we could optically resolve film recalescence after solidification and demonstrate the presence of surface initiated solidification. The fact that both processes could not be resolved by measurements performed with nanosecond resolution confirms the need of sub-nanosecond resolution. q2000 Published by Elsevier Science B.V.