Laser irradiation induced phase change of a new amorphous N:GeSb film is studied by coherent phonon spectroscopy

which is very sensitive to its microstructure. It is found that a new coherent optical phonon(COP) occurs as laser irradiation fluence reaches some threshold

implying laser-induced phase change emerged. Meanwhile

this new phonon also occurs in annealed crystallized N:GeSb film

which proves that the laser irradiation does lead to the crystallization of the N:GeSb film. Pump fluence dependence of COP dynamics of laser-induced crystallized N:GeSb film shows that the frequency and life time of COP decrease as pump energy density increases

which is in accordance with the annealed crystallized N:GeSb film. So it implies the high crystalline quality of the laser-induced phase-change film and the potential application of N:GeSb films in optical phase change memory.