Interference

  • Wavefront splitting: similar study of Young's slits, Fresnel mirrors or Fresnel biprisms: measurement of inter-fringes as a function of different parameters (using an ocular micrometer or CCD strip), temporal coherence (interference in monochromatic and white light) and spatial coherence of the source (influence of slit-source width, visualization of contrast inversion with recording on Caliens CCD).
  • Interference resulting from the reflection at 45° on a glass plate of a spherical wave produced by focusing a laser beam on a small spatial filter: influence of plate thickness and optical quality.
  • Amplitude division: projection of Newton's rings in transmission and reflection, measurement of lens radius of curvature. Projection of interference produced by a soap slide and interpretation of observed colors (bangs of equal thickness).
  • Michelson interferometer :
    1. Settings (determination of optical contact, change from blade to air wedge, change of source: laser, spectral lamp, incandescent lamp).
    2. Measurements in an air gap, using a spectral lamp: law of ring variation in monochromatic light, air gap thickness. Measurement of the Dl of the yellow sodium doublet.
    3. Air wedge measurements: measurement of air wedge angle (in monochromatic light). In white light: Newton's hue scale, fringe deformation by a gas jet, thickness of a microscope slide, analysis of higher-order white using a direct-view prism or CCD spectrometer.
    4. Interferometric measurement of theindex of a gas - variation with pressure: a gas is enclosed in a cylindrical cell, connected to a hand pump and fitted with a pressure gauge. This cell is placed in front of one of the Michelson's two mirrors. We observe the bangs (Michelson rings, laser) as the pressure varies. From this, we can deduce the variation in index with gas pressure. A Mach-Zehnder setup is also available for the same measurement.
    5. Link between source spatial coherence and interference localization.
    6. Estimation of temporal coherence lengths of different sources (high-pressure mercury and low-pressure mercury)
    7. Measuring the pulse width of a pulsed YAG laser
    8. Polarization coherence: Fresnel-Arago experiment.
  • Fabry-Pérot interferometer: finesse is estimated by projecting laser rings onto a Caliens CCD.
  • Application : principle of the interference filter. Influence of the angle of incidence of light on the transmission of a filter (direct observation of the transmitted color with the eye, or use of a spectrometer).
  • Holography :
    1. Virtual image visualization , real image projection from different angles. Creation of holograms.
    2. Recording of transmission holograms (visible by laser only) or reflection holograms (visible in white light). Visualize the displacement or deformation of an object using double-exposure holograms, or by viewing the deformed object through the hologram of the undeformed object produced beforehand.
  • Speckle produced by laser scattering on a frosted screen. We observe the evolution of speckle grain size with the width of the laser beam in the plane of the frosted screen. A software program (Didaconcept) can be used to add together several speckle patterns obtained after a micro-displacement of the object. The resulting TF shows interference bangs, enabling us to deduce the object's displacement.
  • Laser velocimetry: we measure the translational speed of a scattering screen, by measuring the frequency of beats in the intensity of a speckle produced by two laser beams interfering on the screen(Caliens). Planned: measurement of particle velocity distribution in a flow, using the Fourier transform of the spectrum of scattered light mixed with direct light.
Published on March 13, 2017
Updated on March 13, 2017