Abstract

High-order harmonic generation (HHG) in crystalline bulk semiconductors originates from nonlinear intraband currents and interband transitions of the electrons driven by the strong mid-IR electric field. By reducing the size of a semiconductor crystal to nanoscale and making it smaller than the exciton Bohr radius in all three dimensions, quantum dots (QD) are formed with electronic structure distinctly different from the bulk. Spatial quantization of electron and hole motion leads to discrete energy levels instead of a band structure as in the bulk [1]. Therefore, QDs can be considered as artificial atoms and enable transition from atomic/molecular gases to bulk solids. It was predicted recently that the efficiency of HHG in these quantum confined structures is significantly enhanced in comparison to bulk, which is explained by a reduction of quantum diffusion as a result of the reduced amount of the available states [2]. Here, we report on experimental investigation of HHG by mid- IR femtosecond laser pulses in arrays of CdSe QDs as a function of the laser pulse intensity and polarization.

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