Statistical fine structure in the inhomogeneously broadened electronic origin of pentacene in p-terphenyl

Recently, the first observation of statistical fine structure on an inhomogeneously broadened absorption profile was reported [W. E. Moerner and T. P. Carter, Phys. Rev. Lett. 59, 2705 (1987)] for mixed crystals of pentacene in p-terphenyl using laser frequency-modulation spectroscopy. Statistical fine structure is time-independent structure on the inhomogeneous line caused by statistical variations in the spectral density of absorbers in each frequency interval. In this work, a model and an analysis of statistical fine structure using autocorrelation techniques are presented, and the dependence of the effect for pentacene in p-terphenyl at 1.4 K on modulating frequency, detection phase, center concentration, and position in the sample is described. Statistical fine structure provides a new method for probing inhomogeneous systems that allows investigation of the underlying probability distribution function and the determination of the homogeneous linewidth. This fine structure also represents a fundamental limit on the detectability of shallow spectral features in inhomogeneously broadened lines. © 1988 American Institute of Physics.