Femtosecond (fs) laser-induced amorphization of PCM materials. (a) Time-resolved reflectivity of Ge₁₀Sb₂Te₁₃ after a 140-fs laser irradiation. The reflectivity intensity of PCM material decreases within 500 fs and then maintains for at least several tens of ps. (b) Scanning electron micrograph of a GST surface after irradiated by an 18.1-mJ/cm² fs pulse. The dotted circle indicates the irradiated area where grain boundaries can be clearly seen. (c) Time-resolved reflectivity of the GST upon an fs laser irradiation. The data of different fluences are adopted from different areas of a light spot. The red dashed line indicates the reflectivity of liquid phase. (d) Time-resolved white line intensities of XANES of GST during the 600-ps laser-induced amorphization (red dots and line). Obviously, the intensities during amorphization are still far from the intensity of liquid state. Panels (a) and (b) are reprinted with permission from Ref. [29] ©The Optical Society. Panel (c) is reproduced from Ref. [30] with permission from the AIP publishing. Panel (d) is reproduced from Ref. [33] with permission from the American Physical Society.