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首页> 外文会议>Nanotechnology III; Proceedings of SPIE-The International Society for Optical Engineering; vol.6591 >Non-linear optical properties of PECVD Si-nc under nanosecond excitation
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Non-linear optical properties of PECVD Si-nc under nanosecond excitation

机译：纳秒激发下PECVD Si-nc的非线性光学性质

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摘要

A study of the non-linear optical properties of Si-nc embedded in SiO_2 has been performed by using the z-scan method in the nanosecond and femtosecond ranges. Substoichiometric SiO_x films were grown by plasma-enhanced chemical-vapor deposition (PECVD) on silica substrates for Si excesses up to 24 at. %. An annealing at 1250 ℃ for 1 hour was performed in order to precipitate Si-nc, as shown by EFTEM images. Z-scan results have shown that, by using 5-ns pulses, the non-linear process is ruled by thermal effects and only a negative contribution can be observed in the nonlinear refractive index, with typical values around -10~(-10) cm~2/W. On the other hand, femtosecond excitation has revealed a pure electronic contribution to the nonlinear refractive index, obtaining values in the order of 10~(-12) cm~2/W. Simulations of heat propagation have shown that the onset of the temperature rise is delayed more than half pulse-width respect to the starting edge of the excitation. A maximum temperature increase of ΔT = 123.1 ℃ has been found after 3.5 ns of the laser pulse maximum. In order to minimize the thermal contribution to the z-scan transmittance and extract the electronic part, the sample response has been analyzed during the first few nanoseconds. By this method we found a reduction of 20 % in the thermal effects. So that, shorter pulses have to be used to obtain just pure electronic non-linearities.
机译：通过在纳秒和飞秒范围内使用z扫描方法对嵌入SiO_2中的Si-nc的非线性光学性质进行了研究。通过等离子增强化学气相沉积（PECVD）在二氧化硅衬底上生长亚化学计量的SiO_x膜，使Si过量达到24 at。 ％。如EFTEM图像所示，在1250℃下退火1小时以沉淀Si-nc。 Z扫描结果表明，通过使用5 ns脉冲，非线性过程受热效应支配，在非线性折射率中只能观察到负贡献，典型值约为-10〜（-10）厘米〜2 / W另一方面，飞秒激发显示出纯电子对非线性折射率的贡献，获得的值约为10〜（-12）cm〜2 / W。热传播的模拟表明，相对于激发的起始边缘，温度上升的开始被延迟了一半以上的脉冲宽度。在最大3.5 ns的激光脉冲后发现最大温度升高ΔT= 123.1℃。为了最小化对z扫描透射率的热影响并提取电子零件，已在前几纳秒内分析了样品响应。通过这种方法，我们发现热效应降低了20％。因此，必须使用较短的脉冲来获得纯电子非线性。

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