Provides a thorough discussion of the Hanle effect and level-crossing spectroscopy and their applications in many different fields of physics. Includes a translation of Wilhelm Hanle's 1924 paper that first presented the effect, and seven original papers reviewing applications in atomic, molecular,

I am most pleased and, in a way, I feel honored to write the Foreword for the book The Hanle Effect and Level-Crossing Spectroscopy, which covers such a very wide range of applications not only in the initial areas of atomic and molecular physics, but also in solid state physics, solar physics, laser physics, and gravitational metrology. To link these fields together in a coherent way has been the merit of the editors of the book, who attracted most distinguished authors for writing the chapters. In retrospect to Hanle's discovery of quantum mechanical coherence between two quantum states...