Role of material amorphicity in laser-induced phase transition

The crystallization patterns induced by nano- and picosecond laser pulses within an amorphous matrix, with various degrees of relaxation, present morphological instabilities. We show by TEM observations that the final crystalline structures of the relaxed amorphous state, after nanosecond laser excitation, and the “as-deposited” amorphous state after picosecond excitation, present similar morphology. Structurally, metastable crystalline states have been formed under laser irradiation. A probable process for these instabilities is related to competition between the light-induced electronic excitation and thermal processes during the nucleation stage.