Non-resonant optical excitation of mode-locked electron spin coherence in (In,Ga)As/GaAs quantum dot ensemble

Abstract

Two-color pump probe experiments reveal the possibility to use non-resonant pulsed laser excitation to create mode-locking of the ground state electron spin precessions in an ensemble of singly charged (In,Ga)As/GaAs quantum dots. The mode-locking shows a resonance for excitation into the first excited shell while for excitation into higher shells or barriers it disappears; however, spin coherence can still be induced. We conclude that the optically excited carriers relax spin-conserved from the p-shell into their ground states on a picosecond time scale, much shorter than the spin revolution period about the magnetic field.