ABSTRACT
Until the advent of laser, optical spectroscopy was limited to absorption and emission. These linear techniques often provided incomplete information because of the presence of inhomogeneous broadening, which arises in gases from Doppler shifts and in solids from random crystal elds or structural disorder (Figure 10.1). Lasers provided the high intensity needed to implement nonlinear spectroscopic techniques, which can make measurements “below” the
CONTENTS
10.1 Introduction 371 10.1.1 Physical Description of TFWM for a Two-Level System 373 10.1.2 Overview of Variants and Extensions of TFWM 375 10.1.3 Use of TFWM Spectroscopy in Solids, Semiconductors,
and Complex Systems 376 10.2 Theory 377
10.2.1 TFWM Signal from an Inhomogeneously Broadened Ensemble of Two-Level Systems 378
10.2.2 Phenomenological Inclusion of Many-Body Effects 381 10.3 Experimental Details of TFWM 382
10.3.1 Basics of Excitation Pulse Generation, Alignment, and Signal Detection 382 10.3.2 Time-Integrated Two-Pulse TFWM 385 10.3.3 Time and Spectrally Resolved Two-Pulse TFWM 386 10.3.4 Three-Pulse TFWM 386 10.3.5 Co-Linear TFWM 387
10.4 Case Study: TFWM from Excitons in GaAs Quantum Wells 387 10.4.1 Dephasing 388 10.4.2 Many-Body Effects 389 10.4.3 Disorder 391 10.4.4 Quantum Beats 391 10.4.5 Polarization Dependence 392
10.5 Multidimensional Fourier Transform Spectroscopy 392 10.6 Summary 393 References 393
inhomogeneous line width and determine the underlying homogeneous line widths. Often the homogeneous width is more interesting because it reects dynamics such as scattering and/ or radiative decay.
