Abstract:
Numerous Investigations on the phase transition of silicon during picosecond laser annealing have been performed in recent years. it has been well established that the silicon surface melts during a picosecond laser pulse. Because liquid silicon is a metal, the reflectivity of the increases on melting. This has indeed been observed using optical pump-and-probe techniques. Standard picosecond pump-and-probe measurements, however, have some serious inherent drawbacks. First, they cannot resolve reflectivity changes that occur on a time scale of a few picoseconds, because they integrate over the duration of the probe pulse (tyically 20 ps or more). Second, they determine the time probile of the reflectivity for every pump fluence in a step-wise manner by varying the delay beteween the pump and the probe pulse. This introduces a large amount of scatter in the data points, due to shot-to-shot variations in the pump fluence, and requires a large amount of data to be taken for every time probile of the reflectivity. Also, they provide no spatial information on the melting process.To Obtain spatial resolution, a better time resolution, and to measure the time profile of the reflectivity on a single-shot basis, we use a streak camera with a time resolution of 1.8 ps for the detection of the probe pulse.