Nonlinear optics with single molecules

Summary form only given. A single molecule in a crystal matrix is a very good example of a two-level system. We describe a new system for single-molecule spectroscopy. Dibenz-anthanthrene in a naphthalene crystal, which we use to illustrate some effects of the coupling of an electronic two level system to electromagnetic fields. We studied optical saturation and photon bunching due to a metastable triplet level. The triplet population rate and triplet lifetime are so low, that the bottleneck effect of the triplet may be neglected. We also observed variations of the single molecule radiative linewidths.