Introduction

This chapter is devoted to the description of the interaction of polarized light with carrier spins and nuclear spins in semiconductor quantum dots. A historical starting point of these original experiments is the close analogy between quantum dot physics and atomic physics. In 1952, Brossel Kastler and Winter investigated mercury atoms in a weak magnetic field which splits the electron Zeeman levels. By irradiation of the atoms with circularly polarized light the authors could selectively populate one of the electron Zeeman levels [9]. This process has since been referred to as optical pumping. Soon afterwards the first optical pumping of carrier spins in a semiconductor was reported [31]. The initial pumping of spin-orientated conduction electrons in silicon induced by polarized light led to polarization of the nuclear spins of the atoms of the silicon lattice via the hyperfine interaction. This dependence of the nuclear magnetization on the polarization of the absorbed light is at the heart of the experiments described in this chapter. A review of the nuclear spin effects in bulk semiconductors can be found in [37]. The hyperfine interaction between carrier and nuclear spins gives even more spectacular results in quantum dots as shown in pioneering work on optically detected nuclear magnetic resonance ODNMR [23] and orientation of one spin species will have a strong influence on the other [25, 7]. Below we detail a selection of the most remarkable consequences of nuclear spin physics on the optical properties of quantum dots.