Book excerpt: Detailed studies of the low-temperature inhomogeneously broadened 0-0 S(1)-S(0) electronic transition of pentacene dopant molecules in p-terphenyl crystals have produced two novel observations which open up a new regime for ultra-sensitive laser spectroscopy in solids. The first result, direct detection of intrinsic static absorption fine structure on a megaHertzs scale, called statistical fine structure, arises from number fluctuations in the spectral density of absorbers which scale as the square root of the number of absorbers per homogeneous width. Surprisingly, this effect provides a new method for determining the homogeneous width that does not rely on hole-burning or coherent transients. The second recent observation, detection of the optical absorption of a single pentacene molecule in a p-terphenyl crystal, opens the door to new studies of single local environments in solids as well as to studies of the interactions of a single absorber with external perturbations in which no averaging is performed over large numbers of nominally equivalent local configurations. Both achievements utilized high sensitivity variations of laser frequency modulation spectroscopy to perform the measurement. Keywords: Statistical fine structure, Atomic properties, Single molecule detection, Molecule properties, Laser spectroscopy of solids, Instrumentation, Pentacene in p-terphenyl, Organic compounds, Near field.