ABSTRACT
Cardiff University, School of Biosciences, Museum Avenue PO Box 911,
Cardiff CF10 3US, United Kingdom
Wolfgang Langbein
Cardiff Univesity, School of Physics and Astronomy, The Parade, Cardiff
CF24 3AA, United Kingdom
Contents
12.1. Introduction
Nonlinear optical spectroscopy is a powerful technique to investigate the
dynamics of charge carriers in semiconductors and semiconductor nanos-
tructures. More specifically, the third-order nonlinearity probed in four-
wave mixing (FWM) or spectral hole burning experiments can be used to
determine dephasing times even in the presence of large inhomogeneous
broadening where linear spectroscopy usually fails. These nonlinear meth-
ods were extensively used in the 90’s to investigate dephasing of excitons
in semiconductor quantum wells (QWs) [1]. However their application to
epitaxially-grown semiconductor nanostructures of reduced dimensionality
such as quantum wires and quantum dots (QDs) turned out to be quite
difficult due to reasons of both signal strength and directional selectiv-
ity. Transient FWM on localized excitons in GaAs islands [2, 3] and II-VI
epitaxially grown quantum dots [4, 5] was reported in the late 90’s, both
systems exhibiting stronger oscillator strengths (radiative lifetimes of 100-
200ps) than the strongly-confined InGaAs/GaAs self-assembled QDs.
