Statistical fluctuations of the magnetization are measured on the nanometer scale. As the experimental monitor we use the characteristic photoluminescence signal of a single electron-hole pair confined in one magnetic semiconductor quantum dot, which sensitively depends on the alignment of the magnetic ion spins. Quantitative access to statistical magnetic fluctuations is obtained by analyzing the linewidth broadening of the single dot emission. Our all-optical technique allows us to address a magnetic moment of only approximately equal 100 micro(B) and to resolve statistical changes on the order of a few micro(B).

present the results of magnetoluminescence study of ZnSe:CdMnSe quantum dots samples in a magnetic field up to 11 T both in the Faraday and Voigt geometries at liquid He temperatures and various levels of laser excitation. We found that the intensity of the quantum dot photoluminescence strongly increases (up to two orders of magnitude) in the Faraday geometry and only slightly (∼ 1.5 times) in the Voigt geometry within the range of B=0-11 T. We explain the strong increase of the photoluminescence in the Faraday geometry within the frame of the spin-dependent Auger recombination of excitons through Mn ions. We relate the observed anisotropy of the quantum dot emission with the high anisotropy of the hole spins in QDs. We present a theoretical model which allows us to obtain selection rules for the Auger transition and thoroughly explains experimental results. The selections rules allow to explain characteristic fitures in single quantum dot spectra.

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Underlying near-field optical effects on the nanoscale have stimulated the development of apertureless vibrational spectroscopy and imaging with ultrahigh spatial resolution. We demonstrate tip-enhanced Raman spectra of single-walled carbon nanotubes (SWCNTs), recorded with a scanning near-field optical spectrometer using both atomic force (AF) and shear force (SF) feedback lock-in regulation, and critically discuss the advantages and drawbacks of both operation modes. For accurate calculation of the enhancement factor obtained, we have analysed the tip shape and diameter by means of scanning electron and transmission electron microscopy (SEM and TEM). In our experiments we reproducibly attain diameter-corrected and area-corrected enhancement factors of up to ∼10 4 and ∼10 5 , respectively, estimated as the linear ratio of near-and far-field intensities, and we are able to demonstrate near-field Raman imaging of SWCNTs with spatial resolution better than 50 nm.

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