title: Spatial coherence measurement of polychromatic light with modified Young's interferometer.
abstract: Partial spatial coherence is a fundamental concept in optical systems. Theoretically, the normalized mutual coherence function gives a quantitative measure for partial spatial coherence regardless of the spectral nature of the radiation. For narrowband light the degree of spatial coherence can be measured in terms of the fringe modulation in the classic Young's two-pinhole interferometer. Though not commonly appreciated, with polychromatic radiation this is not the case owing to the wavelength dependence of diffraction. In this work we show that with a modified two-beam interferometer containing an achromatic Fresnel transformer the degree of spatial coherence is again related to the visibility of intensity fringes in Young's experiment for any polychromatic light. This result, which is demonstrated both theoretically and experimentally, thus restores the usefulness of the two-pinhole interferometer in the measurement of the spatial coherence of light beams of arbitrary spectral widths.
authors.affiliation: University of Eastern Finland, Department of Physics and Mathematics, P. O. Box 111, FI-80101 Joensuu, Finland. kimmo.saastamoinen@uef.fi
authors.forename: Kimmo
authors.initials: K
authors.lastname: Saastamoinen
authors.forename: Jani
authors.initials: J
authors.lastname: Tervo
authors.forename: Jari
authors.initials: J
authors.lastname: Turunen
authors.forename: Pasi
authors.initials: P
authors.lastname: Vahimaa
authors.forename: Ari T
authors.initials: AT
authors.lastname: Friberg
mesh_terms: D003124:Colorimetry / Q000295:instrumentation*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D007368:Interferometry / Q000295:instrumentation*; D008029:Lighting / Q000295:instrumentation*; D010783:Photometry / Q000295:instrumentation*