Femtosecond laser-induced periodic surface structures revisited: A comparative study on ZnO
Femtosecond laser-induced periodic surface structures revisited: A comparative study on ZnO
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DOI：
10.1063/1.3074106
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发表时间：
2009-02-01
影响因子：
3.2
通讯作者：
Bonse, J.
中科院分区：
文献类型：
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作者：
Dufft, D.;Rosenfeld, A.;Bonse, J.
在空气中用多个线偏振飞秒脉冲(150-200fs，800 nm)辐照氧化锌单晶表面后，观察到具有不同空间特征的激光诱导周期性表面结构(波纹)。对于垂直入射的激光辐射，在接近0.7到接近0.8J/cm(2)的注量范围内，发现了周期(630-730 nm)接近波长、方向垂直于激光偏振的低空间频率LIPS(LSFL)，并且主要是在脉冲数N=100的情况下。对于较低的注量(0.5-0.7 J/cm(2))，在N=100以下的任何给定脉冲数下，都会出现从LSFL特征向高空间频率LIPL(HSFL)形成的急剧转变。HSFL总是平行于LSFL，表现出200到280 nm之间的空间周期，并且完全用LSFL代替脉冲数N>；100。此外，实验研究了入射角对两种LIPSS类型的影响，揭示了不同的行为。给出了HSFL形成过程中表面散射二次谐波产生的实验证据。此外，我们将证明，如果在一个简单的Drude模型的框架下考虑介质材料的光激发(影响其暂态光学性质)以及辐照表面的二次谐波产生，则可以用已有的LIPSS理论的扩展来完全解释ZnO表面的HSFL结构。在此基础上，对现有的飞秒激光诱导LIPSS模型进行了回顾，并解释了为什么在介质和半导体的低能隙激发下，HSFL主要在亚皮秒范围内观察到。
Laser-induced periodic surface structures (LIPSS) (ripples) with different spatial characteristics have been observed after irradiation of single-crystalline zinc oxide surfaces with multiple linearly polarized femtosecond pulses (150-200 fs, 800 nm) in air. For normal incident laser radiation, low spatial frequency LIPSS (LSFL) with a period (630-730 nm) close to the wavelength and an orientation perpendicular to the laser polarization have been found in the fluence range between similar to 0.7 and similar to 0.8 J/cm(2) and predominantly for pulse numbers up to N=100. For lower fluences (0.5-0.7 J/cm(2)), a sharp transition from the LSFL features toward the formation of high spatial frequency LIPSS (HSFL) appears at any given pulse number below N=100. The HSFL are always parallel to the LSFL, exhibit spatial periods between 200 and 280 nm, and completely substitute the LSFL for pulse numbers N>100. Additionally, the influence of the angle of incidence has been studied experimentally for both LIPSS types revealing a different behavior. Experimental evidence for surface scattered second harmonic generation is presented in the regime of HSFL formation. Moreover, we will show that the HSFL structures on ZnO surfaces can be fully explained by an extension of the existing LIPSS theories if the photoexcitation of the dielectric material (affecting its transient optical properties) is considered in the frame of a simple Drude model along with the second harmonic generation at the irradiated surface. Based on our analysis, the current models of femtosecond laser-induced LIPSS are revisited and an explanation is proposed why HSFL are observed predominantly in the subpicosecond range for below band-gap excitation of dielectrics and semiconductors.