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

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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.