ABSTRACT
Many basic condensed matter properties and phenomena are governed by the spectrum of electronic and vibrational degrees of freedom at low energies, comparable to the Boltzmann thermal energy (kBT). They determine both the material’s ground state at nite temperature and its dynamical response to electromagnetic or electronic perturbations. Optical access to these low-energy excitations is the realm of terahertz (THz) spectroscopy: an electromagnetic wave of frequency ν = 1 THz = 1012 Hz corresponds to a photon energy hν ≈ 4.136 meV. As a result, measurement of the THz electromagnetic response in the ≈0.1-50 THz range yields
CONTENTS
11.1 Introduction 397 11.2 THz Generation and Detection 399
11.2.1 Generation of Coherent THz Pulses 399 11.2.2 Electro-Optic Sampling 405 11.2.3 Photoconductive Antennas and Other Schemes 408
11.3 THz Time-Domain Spectroscopy 409 11.3.1 Experimental Setup 410 11.3.2 Dielectric Function Analysis: Thin-Film versus Thick Slab Geometries 412
11.3.2.1 Thick Slab Geometry 413 11.3.2.2 Multilayered Film Geometry 414
11.3.3 Real and Imaginary Conductivity of Superconductors 415 11.4 Optical Pump-THz Probe Spectroscopy 419
11.4.1 Experimental Considerations 420 11.4.2 Transient Dielectric Functions 421 11.4.3 Dynamics of Photoexcited e-h Pairs: Intra-Excitonic Spectroscopy 423 11.4.4 Systems with a Correlated Ground State: Cooper Pair Dynamics 427
11.5 Terahertz Excitation 431 11.6 Summary and Outlook 433 Acknowledgments 434 References 434
insight into a particularly relevant spectrum of excitations in complex materials (Dressel and Grüner, 2002; Basov and Timusk, 2005). These include, for example, the conductivity of itinerant charges, plasmons, and polarons, as well as transitions across internal exciton states, quantized levels of nano-conned carriers, and superconducting gaps.
