Namboodiri Mahesh, Khan Tahir Zeb, Bom Sidhant, Flachenecker Günter, Materny Arnulf
Center for Functional Materials and Nanomolecular Science, Jacobs University Bremen, Bremen, Germany.
Opt Express. 2013 Jan 14;21(1):918-26. doi: 10.1364/OE.21.000918.
Accessing ultrafast photoinduced molecular dynamics on a femtosecond time-scale with vibrational selectivity and at the same time sub-diffraction limited spatial resolution would help to gain important information about ultrafast processes in nanostructures. While nonlinear Raman techniques have been used to obtain highly resolved images in combination with near-field microscopy, the use of femtosecond laser pulses in electronic resonance still constitutes a big challenge. Here, we present our first results on coherent anti-Stokes Raman scattering (fs-CARS) with femtosecond laser pulses detected in the near-field using scanning near-field optical microscopy (SNOM). We demonstrate that highly spatially resolved images can be obtained from poly(3-hexylthiophene) (P3HT) nano-structures where the fs-CARS process was in resonance with the P3HT absorption and with characteristic P3HT vibrational modes without destruction of the samples. Sub-diffraction limited lateral resolution is achieved. Especially the height resolution clearly surpasses that obtained with standard microCARS. These results will be the basis for future investigations of mode-selective dynamics in the near field.
在飞秒时间尺度上以振动选择性且同时具有亚衍射极限空间分辨率来获取超快光致分子动力学信息，将有助于获得有关纳米结构中超快过程的重要信息。虽然非线性拉曼技术已与近场显微镜结合用于获取高分辨率图像，但在电子共振中使用飞秒激光脉冲仍然是一个巨大挑战。在此，我们展示了利用扫描近场光学显微镜（SNOM）在近场中检测飞秒激光脉冲的相干反斯托克斯拉曼散射（fs-CARS）的首个结果。我们证明，在fs-CARS过程与聚（3-己基噻吩）（P3HT）吸收以及P3HT特征振动模式共振的情况下，能够从P3HT纳米结构中获得高空间分辨率图像，且不会破坏样品。实现了亚衍射极限横向分辨率。特别是高度分辨率明显超过了标准显微CARS所获得的分辨率。这些结果将为未来近场模式选择性动力学研究奠定基础。
