We present a comprehensive theory for heterodyne absorption spectroscopy with phase-modulated light. The general equations presented allow for an arbitrary modulation index and an arbitrary modulation frequency. We use this description for three purposes: First, we review the special cases of so-called frequency modulation and wavelength modulation spectroscopy. Second, we present the additional case of large-index, high-frequency modulation. Third, we present an overview of how the absorption signal depends on the experimental parameters of modulation frequency and modulation index. This overview may be helpful to experimentalists in choosing these parameters, for it provides a systematic understanding of how moving around in parameter space changes certain features of the signal, while leaving other features invariant.

Equivalence between focused paraxial beams and the quantum harmonic oscillator Am. J. Phys. 73, 625 (2005) Elementary Quantum Mechanics in One Dimension Am. J. Phys. 73, 480 (2005) The wave function and reality Am. J. Phys. 73, 197 (2005) Quantum harmonic oscillator revisited: A Fourier transform approach Am.

Because of relativistic length concentration, the buoyant force on a submerged projectile depends on its velocity. How this affects the motion of a submerged projectile is considered here. The case considered is highly idealized, yielding a tractable conceptual problem in relativity.