Spatial resolution for two-beam spectroscopy: a new mechanism

With the help of interference effects, two-beam and multiple-beam spectroscopy detect in the pairs of beams (bundles of rays selected by the optical system) phase correlations due to certain fluctuations in optically thin distributions of incoherent light sources. Originally spatial resolution along the line of sight was expected for multiple-beam spectroscopy because of the limited region of intersection for pairs of beams. Here more general analysis shows another mechanism of spatial resolution allowing use of broader overlapping beams. Thus a simpler two-beam spectroscopy configuration (to be discussed in more detail elsewhere) capable of making more efficient use of emitted light proves to offer the same localized measurement of spatially harmonic fluctuations in the appropriate light source distributions.