ABSTRACT
Lasers have become part of our daily life, like food and drink. Of course, laser sources constitute the backbone of laser spectroscopy and imaging, the thread of this book. In this chapter, a brief insight into basic principles and operating parameters of lasers is provided, by and large concentrating on features of key importance for applications in spectroscopy and imaging. After a short introduction (including a few elementary equations) into the principles of how a laser works, the coverage of important laser properties begins with a description of spatial laser-field distributions, including beam profiles and the related transverse electromagnetic modes, as well as laser beam propagation. Thereafter, frequency and spectral characteristics are outlined with regard to bandwidth, and the phenomena of mode structure and line shape and spectral envelops receive particular attention. In conjunction with the frequency content of the laser radiation, its temporal aspects are discussed, highlighting in particular advantages and pitfalls when utilizing continuous-wave or ultrashort light pulses (picosecond- or femtosecond-pulse durations) in spectroscopy and imaging. The chapter concludes with a discussion of polarization and coherence properties of laser beams, pointing out how they can be exploited advantageously in specific spectroscopy and imaging applications.
