Ultrafast imaging of femtosecond laser-induced periodic ripples on the surface of silver film
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摘要: 采用440 nm空间分辨、亚皮秒时间分辨的泵浦探测成像技术,本文研究了800 nm飞秒激光脉冲照射银膜表面后亚波长周期条纹的形成动力学.分析了1~6个飞秒脉冲照射下银膜表面条纹结构的演化过程.第一个激光脉冲在薄膜表面诱导凹槽等缺陷结构;第二个激光脉冲以后表面开始出现亚波长周期条纹,并且在更多脉冲照射时进行纵向和横向生长.条纹在50~70 ps以后开始出现,随延迟时间增加不断加深变长,在演化过程中条纹位置保持不变;形成过程在1 000 ps内基本结束.研究结果表明,飞秒激光在薄膜表面诱导凹槽等缺陷结构在后面的激光脉冲照射表面过程中激发了表面等离激元,进而导致的周期性能量沉积在亚波长周期条纹形成过程中起了关键作用,材料表面的熔化导致了之前形成的条纹变浅以及部分消失.Abstract: This paper studies the dynamics of femtosecond laser-induced periodic ripples on silver film by a time-resolved pump-probe imaging method. After 1-6 pump pulses irradiation, the temporal evolution of the periodic ripples on sample surface is observed. The premier ripples appear in the initial 50-70 ps after the second fs laser irradiation, and the ripple positions keep unmoved until the formation processes is completed in 1 000 ps. The results indicate that the periodic deposition of laser energy during the interaction between femtosecond laser pulses and sample surface plays a dominant role in the formation of periodic ripples, which is caused by the excitation of surface plasmon polariton During the solidification process, some ripples become shallow and even disappear because of surface melting.
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Key words:
- femtosecond laser /
- pump-probe imaging /
- periodic ripples /
- silver film /
- surface plasmon polariton
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图 3 第一个飞秒激光脉冲照射后不同延迟时间样品表面形貌的光学显微照片图, (e) 和 (f) 表示的是同一光斑的图像, 图标代表图片是在泵浦光照射几秒之后测得的
Fig. 3 Optical micrographs of sample surface irradiated by the first pump pulse at different delay times, (e) and (f) are the images of same spot, where the label " $\infty $ " means the picture was observed a few seconds after the irradiation of pump pulse
图 6 (a) 第三个脉冲飞秒激光照射后同一光斑的光学图像, "before"、"after"分别表示脉冲打到样品上不同延迟时间"之前"和"之后"的图像; (b) 表示的是沿着图 6(a) 中对同一位置标记的红色箭头方向的CCD像素的强度分布
Fig. 6 (a) The optical images at the same spot, where the pictures labeled "before" and "after" were obtained a few seconds before or after the arrival of the second pump pulse, respectively, the respective arrows in (a) mark the same position; (b) Shows the intensity of CCD pixels along the arrows in (a)
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