The name is absent

Chapter 1

Introduction

The terahertz (THz) region of the electromagnetic spectrum lies in the gap between
microwaves and infrared. This so-called ’terahertz gap’ has historically been defined
by the relative lack of convenient and inexpensive sources, detectors, and systems for
terahertz waves. For frequencies below about 100 GHz (corresponding to a free-space
wavelength of λ = 3 millimeters), electronic components can be purchased from a
number of commercial suppliers, and millimeter-wave imaging systems are becoming
available. Above 10 THz (λ = 30 microns), thermal (black-body) sources are in-
creasingly efficient means for generating radiation, thermal cameras are commercially
available, and optical techniques become more readily applicable. The two orders of
magnitude of frequency spectrum in between are, relatively speaking, much less well
explored (see Figure 1.1). Meanwhile, imaging with THz radiation offers many advan-
tages such as submillimeter spatial and depth resolution, spectroscopic information,
and unique material responses. Therefore, a wide range of terahertz imaging appli-
cations have emerged in the areas of aerospace, homeland security, medical imaging
and quality control of packaged goods [1].

Terahertz imaging systems have become the subject of intensive research over the
past 15 years. Yet, each of the existing implementations has its own disadvantages
- speed, sensitivity, size, complexity, etc. One traditional method involves a raster-
scan of the object to be imaged in front of the THz beam, while measuring and
recording the transmitted (or reflected) THz wave at each scan position. This me-

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