Near-field optical control of nonlinear properties of single quantum dots

Near-field spectroscopy of self-assembled InGaAs single quantum dots (QDs) is described. For the application of near-field optical microscope to various versions of advanced spectroscopy of single QDs, the functional performance of a near-field fiber probe is much improved. By optimizing the structure of the probe, high sensitivity in signal detection, as well as high spatial resolution, is successfully achieved. In combination with a standard pump-probe spectroscopic techniques, we realize nonlinear absorption spectroscopy of single QDs at low temperature. The absorption cross section of a single QD is effectively modified by local injection of a few electrons into the QD. Employing a femtosecond pulsed laser, time-resolved photoluminescence spectroscopy is also performed.