Lasers are playing a more and more dominant role in modern optical spec- troscopy, offering an increased potential for high resolution and, thus, for more detailed spectroscopic information on dynamic and structural param- eters. This book on Zero-Phonon Lines and Spectral Hole Burning in Spec- troscopy and Photochemistry gives a concise and very useful survey of some of the pioneering and current work on solid state spectroscopy of various groups in the USSR. It focusses on the optical Mossbauer analogue, the "zero-phonon line", and "hole burning" spectroscopy, a method which increases the resolu- tion well beyond the zero-phonon linewidth. In this conte. . 'Ct, the present work is complementary to Persistent Spectral Hole-Burning: Science and Applica- tions (ed. by W. E. Moerner, Springer, Berlin, Heidelberg 1988), which deals in more detail with the various aspects of laser spectroscopy with ultrahigh spectral resolution. Zero-phonon lines and an understanding of the various phonon coupling mechanisms which are treated in this book are a prerequi- site for applying and understanding techniques of ultrahigh resolution such as hole-burning or optical echoes. Bayreuth, March 1988 D. Haarer Preface The investigation of zero-phonon lines (ZPLs) is one of the foremost and most informative fields of present-day condensed-matter spectroscopy. Along with its definite function in physical cognition and investigation methods, the spectroscopy of ZPLs is also gaining purely practical applications. This is due to the fact that ZPLs are extra-sensitive quantum-mechanical detectors.
