The problem of determining the parameters of a resonance signal from observations of the output of a lock-in detector is considered for the cases in which the resonance has a Lorentz or dispersion line shape. Computer techniques are applied to the more general superimposed line-shape problem accommodating modulation broadening, time-constant distortion, and the effects of multiple overlapping components. Analytical expressions are obtained for several special cases.
R. LOWELL SMITH, "Practical Solutions of the Lock-In Detection Problem for Lorentz and Dispersion Resonance Signals," J. Opt. Soc. Am. 61, 1015-1022 (1971)