Development of nonlinear near-field scanning optical microscope and its application to the study of optical nonlinearlties of semiconductor quantum structures

利用近场扫描光学显微镜和超快激光脉冲相结合，可以在近场光纤探针的孔径周围产生时域和空域的强电场。利用这一优点，可以容易地在材料中诱导非线性光学响应。我们研制了一种新型的光学显微镜（非线性近场扫描光学显微镜），研究了半导体量子结构中光学响应的非线性行为。本课题的主要研究成果如下：1.在近场扫描光学显微镜上增加了脉冲群速度色散补偿系统。通过减小光纤探针中光脉冲的展宽，构建了非线性近场扫描光学显微镜。2.采用冲击法可以制备孔径为20-30 nm的双锥光纤探针。由于这种近场光纤探针的高性能，在半导体量子结构的测量中实现了30 nm的高空间分辨率。3.半导体量子点中的库仑相互作用由于载流子被限制在纳米空间中而增强。我预期只要在半导体量子点中产生少量的载流子，就可以容易地诱导出非线性光学响应。研究了室温下单个InGaAs量子点在较高激发条件下的光致发光谱。发现了量子点中的多体效应和俄歇散射导致的相位弛豫时间的缩短。4.利用空间分辨率为30 nm的近场扫描光学显微镜，实现了GaAs量子点中激子波函数的实空间映射。

With combination of near-field scanning optical microscope and ultra-fast laser pulses, we can create the strong electric field in time and spatial domain around the aperture of the near-field fiber probe. Using this advantage, the nonlinear optical response can be easily induced in the materials. We have developed the new type of optical microscope (nonlinear near-field scanning optical microscope) and investigated the nonlinear-behavior of the optical response in semiconductor quantum structures. The results of this research project are as follows.1.I have added the compensate system of group velocity dispersion of the pulse to the near-field scanning optical microscope. The nonlinear near-field scanning optical microscope has been constructed due to reduction of the optical pulse broadening in the fiber probe.2.The double tapered fiber probe with a 20-30 nm aperture can be fabricated using pounding method. The high spatial resolution of 30 nm in the measurement of semiconductor quantum structures has been achieved owing to the high performance of this near-filed fiber probe.3.The Coulomb interaction is enhanced in a semiconductor quantum dot, because the carriers are confined in a nanometer space. I expect that the nonlinear optical response can be easily induced, if only a few carriers are generated in a semiconductor quantum dot. I investigated the photoluminescence spectrum of a single InGaAs quantum dot at room temperature in the higher excitation conditions. The many body effects and the decrease of phase relaxation time due to Auger scattering process in a quantum dot have been found.4.I have demonstrated the real-space mapping of exciton wave function confined in a GaAs quantum dot using the near-field scanning optical microscope with a 30 nm spatial resolution.