Nanosecond resolution time-resolved x-ray study of silicon during pulsed-laser irradiation

We have used the pulsed time structure of the Cornell High-Energy Synchrotron Source (CHESS) to carry out a nanosecond resolution time-resolved x-ray study of silicon during pulsed-laser irradiation. Time-resolved temperature distributions and interfacial overheating and undercooling were measured on <111> and <100> silicon during 25 ns UV laser pulses through the analysis of thermal expansion induced strain. The temperature gradients were found to be >107 K/cm at the liquid--solid interface and the temperature distributions have been shown to be in agreement with numerical heat flow calculations for these laser conditions. The combined overheating and undercooling (during approx.10 m/s melting and approx.6 m/s regrowth) was measured to be 110 +- 30 K on <111> oriented silicon and 50 +- 25 K on <100> silicon. These values have been interpreted in terms of velocity coefficients of overheating and undercooling